Separations doi: 10.3390/separations13050140

Authors: Yanxin Xie Jiuyang Lin Yinhua Wan Chao Wang Kaibo Hu Wenjing Yuan Ning Li Xuewei Li

The treatment of high-salinity wastewater generated from the use of sodium hydroxide (NaOH) in rare-earth metallurgy poses significant environmental and resource-recovery challenges. Conventional methods are often economically unfeasible due to their high energy consumption and limited value recovery. To address these limitations, this study proposes an innovative integrated electrochemical process designed not only to desalinate the wastewater efficiently but also to valorize it through the simultaneous co-production of NaOH, chlorine (Cl2), and hydrogen (H2). Systematic optimization reveals a critical trade-off between ion transport efficiency and side reactions, with optimal performance achieved at 2 mol L−1 NaCl, 80 mA cm−2 current density, 2 mm electrode spacing, 30 mL min−1 flow rate, and 5000 mg L−1 initial NaOH concentration. The system maintains exceptional long-term stability, sustaining 97.5% Cl− removal over 4410 min of continuous operation without membrane fouling, a key advantage over conventional processes. Validation with authentic rare earth wastewater achieves 90.3% desalination within 5 h. Techno-economic analysis shows that the market value of recovered NaOH nearly offsets the energy cost, achieving near-cost-neutrality. This work establishes electrolysis–membrane coupling as a technically viable and economically attractive strategy for transforming high-salinity industrial waste streams into valuable resources.

Separations doi: 10.3390/separations13050139

Authors: Xinhan Fan Wei Wang

Elaeagnus angustifolia L., belonging to the family Elaeagnaceae and genus Elaeagnus, which is a medicinal and edible homologous material with significant economic and ecological value. Its polysaccharides are one of its key active components, exhibiting bioactivities, including antioxidant, immunomodulatory, antitumor, anti-fatigue, and hypolipidemic effects. This paper reviews the research progress on the extraction, purification, structural features, and bioactivities of E. angustifolia polysaccharides, aiming to provide a theoretical basis and reference for their high-value development and utilization.

Separations doi: 10.3390/separations13050138

Authors: Tijana Radojičić Katarina Trivunac Marina Maletić Ivona Janković-Častvan Miloš Simić Ana Kalijadis Marija Vukčević

In this study, carbonaceous and hybrid adsorbents were synthesized from waste flax fibers and fly ash, integrating two abundant waste streams into a single functional material. Materials were thermally modified and activated with NaOH at 500 °C in a nitrogen atmosphere. The prepared adsorbents exhibit high efficiency for scandium ion removal, with the hybrid systems significantly outperforming the individual components. The obtained Langmuir maximum adsorption capacities for the adsorption of scandium onto hybrid adsorbents were 18.28 and 32.32 mg/g, depending on the flax fibers/fly ash ratio. The contrasting thermodynamic behavior between hybrid adsorbents of different composition highlights the significant influence of material structure on the adsorption mechanism. The results demonstrate that the synergistic integration of waste flax fibers and fly ash in hybrid materials produces efficient and environmentally sustainable adsorbents, offering a novel approach for REE recovery from aqueous systems.

Separations doi: 10.3390/separations13050137

Authors: Jhapindra Adhikari Gehui Pang Shintaro Morisada Hidetaka Kawakita Keisuke Ohto Mikihide Demura Kazuya Urata

Four algal adsorbents were prepared from two types of green sea algae (Ulva lactuca and Ulva pertusa), either by treatment with concentrated sulfuric acid or without treatment. A comparative study of Au(III) adsorption in an HCl medium was performed. While both untreated adsorbents showed good performance at low HCl concentrations, the treated adsorbents achieved quantitative adsorption and high selectivity for Au(III) across a broad range of HCl concentrations. The adsorption of Au(III) onto the algal biomass adsorbents followed the typical Langmuir monolayer adsorption model. At an HCl concentration of 0.010 M, the maximum adsorption capacities were 1.14, 0.86, 6.57, and 6.28 mol kg–1 for DUL, DUP, TUL, and TUP, respectively. A kinetic study conducted at different temperatures was consistent with the pseudo-first-order kinetic model and enabled estimation of the activation energy of the adsorption reaction. Structural changes before and after treatment were analyzed using FT-IR spectroscopy. Confirmation of Au(III) adsorption and its subsequent reduction to the elemental state was achieved through XRD and SEM/EDX analyses as well as digital imaging of the Au-loaded adsorbents. Finally, the adsorbed and reduced Au was successfully desorbed using an acidic thiourea solution.

Separations doi: 10.3390/separations13050136

Authors: Weihui Xu Xueying Li Guangjin Zhao Weishu Wang Kun Zheng Yulu Zhang Yue Wang Yunlong Duan

The growing demand for portable power has triggered a sharp increase in end-of-life lithium–nickel–cobalt–manganese oxide (NCM) batteries. Efficient recovery of NCM cathode materials is crucial for resource security. This study investigates an ascorbic acid–tartaric acid leaching system for extracting cobalt and manganese from spent NCM batteries. Temperature influences the leaching efficiencies of cobalt and manganese. Leaching efficiencies increase from 50 to 80 °C, consistent with the Arrhenius law. However, beyond 80 °C, side reactions inhibit cobalt leaching. Leaching efficiency increases with time over the range of 40 to 120 min, and then stabilizes at equilibrium. Ascorbic acid concentration plays a critical role. Within 0–1.5 mol/L, ascorbic acid promotes dissolution through reduction and coordination. At higher concentrations, excess H+ ions hinder complex formation. Similarly, tartaric acid concentration has an optimum range of 0.2–0.5 mol/L, where both H+ and ligands are supplied effectively. Outside this range, ligand availability is reduced. The solid–liquid ratio also affects performance. The optimal range of 5–15 g/L promotes mass transfer. Outside this range, efficiency declines due to solid accumulation or reduced diffusion. The results show that under optimal conditions, leaching recovery reaches 94.8% for Co and 99.3% for Mn. The optimal leaching conditions were determined as follows: tartaric acid, 0.5 M; ascorbic acid, 1.5 M; liquid-to-solid ratio, 15 g/L; stirring speed, 300 rpm; temperature, 80 °C; and leaching time, 120 min. This system represents a promising laboratory-scale approach for recovering cobalt and manganese from spent NCM batteries, pending further validation in larger-scale studies.

Separations doi: 10.3390/separations13050135

Authors: Hong-Hu Tang Chuan-Yu Liao Xiong-Xing Zhang Li Wang Qing-Jun Guan Yang Cao Wei Sun

Stone coal is an important vanadium-bearing resource and a potential source of rare earth elements (REEs). Previous studies have mainly focused on the bulk occurrence, resource potential, and leaching behavior of V or REEs in stone coal, whereas the microscale spatial relationships between V and REEs and their evolution during leaching remain poorly constrained. In this study, three representative stone coal samples were analyzed by synchrotron radiation micro-X-ray fluorescence (μXRF) to characterize the microscale distributions of V and REEs in raw samples and corresponding leaching residues. Pearson correlation analysis was further used to quantify changes in V–REE spatial relationships during leaching. The results showed that V–REE relationships were generally weak and were modified to different extents after leaching. In the GZ sample, the V–Eu correlation coefficient decreased from 0.63 to 0.34, indicating that the migration of V and REEs was not fully synchronized. The three samples also showed different REE distribution tendencies after leaching: GZ showed partial transfer of REEs to the leachate with residual retention, PX showed mixed behavior with appreciable retention in the residue, whereas PZ retained REEs predominantly in the residue. These results suggest that the integrated utilization of V and REEs in stone coal can be better achieved through a staged recovery route, in which the REE recovery pathway is determined according to their actual distribution between the leachate and the residue after V leaching. This study provides a microscale basis for the comprehensive utilization of coal-related critical metal resources.

Separations doi: 10.3390/separations13050134

Authors: Maria Beatriz Pereira Joana M. N. Sá Gonçalo C. Justino Alexandre Quintas Nuno R. Neng

Cannabis is the most widely consumed illicit substance worldwide, and the rise of synthetic and semi-synthetic cannabinoids poses growing public health concerns due to their high potency and unpredictable effects. This study presents a new analytical methodology for the simultaneous determination of natural and semi-synthetic cannabinoids (cannabidiol (CDB), Δ8-tetrahydrocannabinol (∆8-THC), Δ9-tetrahydrocannabinol (∆9-THC), and hexahydrocannabinol (HHC)) in saliva using gas chromatography coupled with mass spectrometry (GC-MS) in combination with bar adsorptive microextraction (BAμE) as a green sample preparation. The optimized method showed satisfactory recoveries (57.3–80.6%), low detection and quantification limits (1.25 and 4.13 ng/mL, respectively), excellent linearity (r2 ≥ 0.9963), and robust precision and accuracy. Application to authentic saliva samples demonstrated cannabinoid levels consistent with literature values. Overall, the proposed methodology offers a cost-effective, miniaturized, and environmentally sustainable platform for routine oral fluid cannabinoid analysis, highlighting its potential for forensic, clinical, and toxicological applications.

Separations doi: 10.3390/separations13050133

Authors: Yong Bai Xiaoli Zhao Dengxin Li Fang Li

Solar interfacial evaporation is promising for freshwater production, yet thermodynamic energy limits and mass transfer attenuation in high-salinity environments restrict practical applications. To address these challenges, a 3D high-efficiency evaporator is developed by cross-linking a hydrophilic composite gel onto a macroporous sponge scaffold. This spatially decoupled architecture enables fundamental water-state regulation and efficient environmental heat harvesting. Specifically, hydrophilic functional groups in the gel network reduce the equivalent enthalpy of vaporization of water to 1181.8 J g−1. Simultaneously, the 3D columnar structure induces a sidewall cold sink effect to extract additional ambient thermal energy. Through this synergy, the PCPH delivers a remarkable apparent evaporation rate of 8.59 kg m−2 h−1 under one standard sun. Furthermore, interconnected macropores within the sponge establish excellent convective pathways for rapid ion diffusion. Consequently, the device operated continuously for 8 h in a 10 wt% NaCl solution without significant blockage and decreased key metal ion concentrations in 3.5 wt% simulated seawater by 4 to 5 orders of magnitude. The purified water fully satisfies World Health Organization standards. This study offers an innovative strategy to surpass conventional photothermal bottlenecks and design highly durable water treatment materials.

Separations doi: 10.3390/separations13050132

Authors: Qian Cheng Yongxiang Wang Xiangyu Liu Wenxi Zhang Panfeng Gao

Recycling spent lithium-ion batteries (LIBs) is critical for resource sustainability and carbon neutrality. This work presents a green strategy in which NaA zeolite is used to preferentially recover lithium from leachate of spent NCM111 batteries, combined with temperature-regulated stepwise separation of transition metals. Benefiting from the distinct hydrated ionic radii and charge density between Li+ and divalent metal ions, NaA zeolite selectively adsorbs Ni2+, Co2+ and Mn2+, leaving Li+ in the raffinate. Under optimized conditions, two-stage adsorption achieves 95.6%, 96.7% and 99.7% removal of Ni2+, Co2+ and Mn2+, respectively, with 11% Li+ co-adsorption. Thermodynamic analysis reveals that the adsorption process is endothermic and thermodynamically spontaneous. The interaction strength between metal ions and NaA zeolite follows the order Ni2+ > Co2+ > Mn2+, and ion exchange is identified as the dominant mechanism. It is determined that 96.8% of Mn2+ can be recovered at 0 °C, followed by the desorption of 93.5% of Co2+ at 90 °C, and the sequential separation of Mn, Co and Ni is realized. Three consecutive adsorption–desorption cycles demonstrate the acceptable reusability of the Ni-loaded NaA adsorbent. High-purity Li2CO3 (purity 96.7%, yield 93.5%), MnO2 (purity 99.3%, yield 98.4%) and Co3O4 (purity 98.8%, yield 97.6%) are obtained from the corresponding solutions. This approach provides a scalable closed-loop pathway for full-component recovery of valuable metals from spent LIBs.

Separations doi: 10.3390/separations13050131

Authors: Haolei Wu Feng Wei Huagang Ni

Crude fidaxomicin contains difficult-to-separate impurities, and conventional dual-step purification usually requires intermediate concentration and transfer, which increases process complexity and may aggravate product loss or degradation. To address this challenge, this study exploits the complementary selectivity of methanol/water (80/20, v/v) and acetonitrile/water (70/30, v/v) binary mobile phases and proposes two purification processes based on step-gradient twin-column recycling chromatography, namely spatial integration and system integration. In the spatial integration strategy, dual-stage separations that are conventionally performed in separate chromatographic systems are sequentially integrated into a single twin-column recycling system in combination with on-line heart-cutting, thereby eliminating intermediate off-line processing steps. In contrast, the system integration strategy merges the two binary mobile phases in defined proportions to construct a single ternary mobile phase composed of methanol/acetonitrile/water (37.5/37.5/25, v/v/v), enabling one-step complete separation. The results demonstrate that the spatial integration strategy, employing binary mobile-phase switching, produces fidaxomicin with a purity of 99.9%, recoveries ranging from 75.27% to 78.77%, and productivities ranging from 307.22 to 328.82 g·L−1·day−1, regardless of the switching sequence. The system integration strategy, based on one-step elution with the ternary mobile phase, achieves the same product purity of 99.9% without mobile-phase switching, with a recovery of 70.41% and a productivity of 246.33 g·L−1·day−1. These results confirm the applicability and flexibility of both integrated strategies for fidaxomicin purification, while indicating that the spatial integration strategy provides better overall preparative performance and the system integration strategy offers a simpler one-step operation.

Separations doi: 10.3390/separations13050130

Authors: Yanlin Wu Lanhua Luo Yuan Li Shanghua Shi Xiaoning Wang Wenbo Dong Gilles Mailhot

Over the past 20 years, the iron-activated persulfate systems have been widely used for removing pharmaceuticals and personal care products (PPCPs) from water. However, slow Fe(III)/Fe(II) redox cycling and precipitation of iron, unless in very acidic conditions, were the main limitations. Thus, two ligand-assisted Fe(III)/persulfate systems, Fe(III)-acetohydroxamic acid (AHA)/peroxydisulfate (PDS) and Fe(III)-nitrilotriacetic acid (NTA)/peroxymonosulfate (PMS), were comparatively investigated for the degradation of atenolol (ATL) in this study. The experimental results showed that the Fe(III)-NTA/PMS system worked much better than the AHA system. However, the cost of PMS is higher than that of PDS, which should be considered. The primary advantage of the NTA system was its ability to overcome the pH limitations. It worked well over a wide pH range (3.0–10.0), whereas the AHA system could only be used in a narrower pH window (pH 2.4 to 6.5). The investigation of radicals that contributed to ATL degradation revealed that sulfate radicals (SO4•−) were dominant in the NTA system, while hydroxyl radicals (•OH) and SO4•− were the primary and secondary radicals in the AHA system. These results provided useful insight into the comparative behavior of two ligand-assisted Fe(III)/persulfate systems for ATL degradation, with the Fe(III)-NTA/PMS system showing clear potential under neutral or near-neutral conditions, while Fe(III)-AHA/PDS may still represent a lower-cost option under acidic conditions.

Separations doi: 10.3390/separations13050129

Authors: Song Huang Yusong Zhang Bingdi Cao

Sludge electro-dewatering has emerged as a research hotspot in advanced sludge treatment due to its ability to effectively remove interstitial water that is difficult to separate by mechanical dewatering. This paper systematically reviews the fundamental principles, key influencing factors, evolution of electrode materials, and engineering applications of electro-dewatering technology. Emphasis is placed on analyzing the effects of sludge properties, electric field parameters, and electrochemical reactions on dewatering efficiency. The characteristics and applicable scenarios of three generations of electrode materials—from conventional metal electrodes and carbon-based materials to dimensionally stable anodes (DSA)—are summarized. Current challenges include insufficient electrode stability, the trade-off between energy consumption and efficiency, limited understanding of underlying micro-scale mechanisms, and difficulties in process scale-up. Future efforts should focus on the development of high-performance electrode materials, investigation of multi-field coupling enhancement mechanisms, establishment of machine learning-based intelligent control strategies, and engineering design of continuous electro-dewatering equipment to promote its large-scale application in sludge treatment and disposal.

Separations doi: 10.3390/separations13050128

Authors: Miaomiao Huang Qing Wang Shuai Wang

The separation of rare earth elements (REEs) is challenging due to their similar chemical properties. This study developed a series of novel polystyrene–ion-imprinted poly(hydroxamic acid) interpenetrating polymer networks (PS-IIPHAs) for the highly selective adsorption of La3+, Ce3+, and Y3+. The effects of the solution pH, contact time, initial concentrations, and temperature on the adsorption performance of the resins were systematically investigated. The results showed that adsorption equilibrium was reached within 4 h at a pH of 1.0, following the Langmuir isotherm, with maximum adsorption capacities of 2.425, 3.012, and 2.927 mmol/g for La3+, Ce3+, and Y3+, respectively. The resins exhibited excellent selectivity toward the template ions, with separation factors of 35.45 for Ce3+-La3+, 17.52 for Y3+-La3+, and 11.04 for Ce3+-Y3+. These results indicate PS-IIPHAs as promising adsorbents for the efficient, highly selective recovery of REEs.

Separations doi: 10.3390/separations13040127

Authors: Qiang Geng Tianshi Lan Guoqiang Huang

With the increase in the demand for electronic-grade high-purity silane in the semiconductor chip industry, it is of great significance to develop a green and economical method for silane production. Therefore, a novel energy-saving fixed-bed process was proposed innovatively. In this paper, the thermodynamics and kinetics of the trichlorosilane disproportionation system were studied, and the optimal reaction conditions for the resin catalyst were determined, which were used for the subsequent simulation. Based on the conventional DR1 + DR2 process (which includes one trichlorosilane disproportionation reactor (DR1) and one dichlorosilane disproportionation reactor (DR2)), by adding an additional disproportionation reactor to the TCS recycle loop and/or DCS recycle loop, three improved process configurations were designed, including 2DR1 + DR2, DR1 + 2DR2, and 2DR1 + 2DR2 processes. Then, combined with four-column heat integration, the HI + 2DR1 + 2DR2 process was proposed to solve the bottleneck problems of high energy consumption and large circulation flow rate. The results show that the HI + 2DR1 + 2DR2 process achieved the best energy-saving effect. The TCS recycle loop flow rate reduced by 36.87%, the DCS recycle loop flow rate reduced by 12.41%, total energy consumption decreased by 62.8%, and CO2 emissions decreased by 56.72%. The unit energy consumption is 13.8 kg steam/kg SiH4, and the silane purity is greater than 99.9999%. This design can be easily applied to the existing production process of the silane plant, achieving energy-saving and low-cost production of silane.

Separations doi: 10.3390/separations13040126

Authors: Yining Wang Yinghua Sun Wuying Li Shuqian Xia

A water acetone biphasic extraction system was developed for the separation and purification of erythromycin thiocyanate. Response surface methodology based on a Box-Behnken design was used to evaluate the effects of pH, liquid-to-solid ratio, extraction temperature, and acetone-to-water volume ratio on mass yield. All four variables influenced the extraction performance, and acetone-to-water volume ratio and liquid-to-solid ratio were the most significant factors. Under the optimized conditions of 50.5 °C, pH 9.2, a liquid-to-solid ratio of 3.0 mL/g, and an acetone-to-water volume ratio of 2.5 mL/mL, the mass yield reached 81.58 percent. The predicted and experimental values were in good agreement, confirming the adequacy of the model. The product obtained under the optimized conditions met the relevant requirements of the Chinese Pharmacopoeia. The proposed process is simple and effective, and provides a basis for the purification and scale up of erythromycin thiocyanate and related derivatives.

Separations doi: 10.3390/separations13040125

Authors: Kayla Laguana Sonia Egenberger Jack Tobin Claudia Wong Logan Lu Jack G. Webster Mingheng Li

This study investigates how sintering temperature affects phase evolution, titanium carbide (TiC) formation, and oil-repellent performance in TiO2–carbon-coated 304 stainless-steel mesh for oil–water separation applications. Coated meshes sintered at 400, 500, 600, 700, and 800 °C were evaluated using gravity-driven oil permeation tests with 5W-20 motor oil and oil contact-angle measurements, while coating morphology, composition, and phase evolution were characterized by SEM, EDS, and XRD. Sintering temperature strongly influenced coating structure and wettability. Among the tested conditions, the mesh sintered at 600 °C showed the highest oil contact angle (105°) and the highest initial oil retention efficiency (80%), indicating the most favorable balance between oleophobicity and coating stability within the tested range. XRD analysis showed that 600 °C corresponded to the onset of the anatase-to-rutile transition and the initial formation of TiC. These results suggest that intermediate sintering temperatures can provide a favorable balance between retention of beneficial anatase content and enhanced interfacial interaction within the TiO2–carbon coating. Within the tested conditions, 600 °C was the best-performing sintering condition among the temperatures examined for this coating system.

Separations doi: 10.3390/separations13040124

Authors: Chaoyong Li Hui Zhou Haisheng Li Yinghua Chen Ziyin Xu Jie Li Qiqiang Gao Qiang Zhao

As an efficient dry separation technology, electrostatic separation exhibits significant potential for application in the sorting and recovery of carbon-rich resources from coal gasification fine slag (CGFS). The small particle size and high moisture content of CGFS particles are the main factors affecting the efficiency of separation. This study proposes a method integrating particle moisture reduction and charging promotion based on molecular sieves, with the aim of investigating its feasibility in improving the electrostatic separation efficiency of CGFS particles. The results indicate that molecular sieves can effectively adsorb moisture from the ambient humid air and the surface of particles, allowing for rapid drying of wet particles. The reduction in moisture content on the particle surfaces significantly promotes their charging capability, creating favorable conditions for electrostatic separation. After molecular-sieve-assisted charging enhancement, the carbon content in the ash-enriched positive plate product decreased by 4.96%, while the carbon content in the carbon-enriched negative plate product increased by 12.15%, indicating a significant improvement in carbon–ash separation efficiency. Correspondingly, the decarbonization efficiency of the positive plate and carbon recovery efficiency of the negative plate were increased by 21.30% and 52.17%, respectively. Furthermore, when the moisture content exceeds 10%, the phenomenon of inter-particle agglomeration can adversely affect the separation of carbon and ash particles. The most suitable operating conditions are a moisture content no higher than 10%, an electric field density of 30 kV/m, a filling molecular sieve of 400 g, and a gas velocity of 12 m/s (volumetric flow rate 84.78 m3/h). In practical industrial applications, it is advisable to consider pre-treating the particles for drying or employing secondary separation to enhance sorting accuracy.

Separations doi: 10.3390/separations13040123

Authors: Tong Liu Fei Zhu Xijun Tian Zhenping Cai Kai Huang Song Chen

This study addresses the issue of insufficient product purity caused by the co-deposition of three major impurity ions—zinc, nickel, and lead—during the electrodeposition process of high-purity manganese. A targeted deep purification method for manganese sulfate electrolyte was developed using dithiocarbamate chelating agents (sodium dimethyldithiocarbamate, SDD). By optimizing key process parameters such as precipitant concentration, reaction temperature, reaction time, and solution pH, combined with density functional theory (DFT) calculations, to elucidate the selective impurity removal mechanism at the molecular level, a novel process for the efficient synergistic removal of Zn2+, Ni2+, and Pb2+ was established. The results showed that under the conditions of precipitant concentration of 1 g/L, solution pH of 6.5, reaction temperature of 55 °C, and reaction time of 2 h, the residual concentrations of Zn, Ni, and Pb in the electrolyte were all below 0.2 mg/L. DFT calculations revealed that SDD coordinates with metal ions through four sulfur atoms, and the absolute values of binding energies follow the order Ni2+ > Pb2+ > Zn2+ > Mn2+, indicating thermodynamically preferential capture of impurity ions. After purification, the manganese metal obtained by electrodeposition from the manganese sulfate solution achieved a purity exceeding 99.999%, with Zn, Ni, and Pb contents of 0.11 mg/kg, 0.038 mg/kg, and 0.05 mg/kg, respectively, meeting the raw material requirements for semiconductor-grade copper–manganese alloy targets.

Separations doi: 10.3390/separations13040122

Authors: Salim Mokraoui Lahssen El Blidi Irfan Wazeer Attiyah A. Al-Zahrani Mohamed K. Hadj-Kali

This study demonstrates the high efficiency and selectivity of p-toluenesulfonic acid-based deep eutectic solvents (DESs) for simultaneous extractive denitrogenation (EDN) and desulfurization (EDS) of model fuel. Three DESs—TBPB:PTSA, TBAB:PTSA, and ChCl:PTSA (1:1 molar ratio)—were synthesized and evaluated for their effectiveness against representative heteroaromatic pollutants: thiophene, dibenzothiophene, pyridine, and carbazole. The phosphonium-based TBPB:PTSA exhibited the highest extraction performance, achieving over 96% removal of nitrogen species and up to 85% removal of sulfur species at 40 °C. Increasing the temperature enhanced desulfurization by reducing viscosity, thereby improving mass transfer kinetics. Additionally, a 3:1 ratio of DES to fuel provided an optimal balance between solvent economy and operational efficiency. Denitrogenation was driven by strong acid–base protonation facilitated by PTSA, while desulfurization was governed by π–π and dispersion interactions, modulated by the hydrophobicity of the cations. The DES achieved nearly quantitative nitrogen removal and satisfactory sulfur extraction after three reuse cycles, while multistage operation enabled complete purification within four extraction steps. 1H NMR analysis confirmed that no DES components were found in the raffinate phase, verifying the immiscibility and stability of the solvent. These results indicate that TBPB:PTSA is a robust, regenerable, and environmentally benign solvent, effectively enabling simultaneous EDN–EDS of hydrocarbon fuels and positioning it as a promising green alternative to traditional hydrogen-based refining methods.

Separations doi: 10.3390/separations13040121

Authors: Diana Samantha Villarreal-Lucio Karla Ximena Vargas-Berrones Brenda V. Loera-García Vanessa Sarahí Galván-Romero Carolina López-Saldaña Raúl Ocampo-Pérez Héctor Hernández-Mendoza Rogelio Flores-Ramírez

This research focused on the development and characterisation of molecularly imprinted polymers (MIPs) modified with titanium dioxide (TiO2) for the adsorption and photocatalytic degradation of sodium naproxen (NPX). Different percentages of TiO2 (5% and 25%) were tested and compared to non-imprinted polymers (NIPs). FT-IR analysis confirmed the interaction between methacrylic acid and TiO2, promoting the formation of specific binding sites and presenting a good imprinting factor. The results showed that the MIP with 5% TiO2 had the highest adsorption and retention capacity, attributed to the imprinting effect and the reduced interference from TiO2. The surface of the MIPs is heterogeneous, as it was indicated by the Freundlich isotherm model. The KF for the MIP with 25% of TiO2 was higher than for the materials with 5%; values for the MIP/TiO2 5% and the NIP/TiO2 5% KF were 4.808 and 4.163 (mg/g)(L/mg)1/n respectively, while for the MIP/TiO2 25% was 6.542 (mg/g)(L/mg)1/n and for the NIP/TiO2 25% it was 2.736 (mg/g)(L/mg)1/n. Kinetic studies followed the pseudo-second-order model, suggesting more active binding sites in MIPs. Photocatalytic experiments achieved 60% degradation, demonstrating the degradation performance of MIPs; however, this behavior is restricted by the slow degradation of NPX. The materials were evaluated using a water sample (Querétaro River, México); the sample was preconcentrated and analyzed, detecting a concentration of 0.332 mg/L of NPX. This finding highlights the MIPs’ potential application in environmental monitoring and treatment; nevertheless, due to the recalcitrant nature of NPX, MIPs should be used along with other advanced treatment methods to achieve effective removal.

Separations doi: 10.3390/separations13040120

Authors: Mengmeng Jia Mengchen Shi Yi Wang Xiaofeng Fang

The efficient removal of dyes and separation from dissolved salts are crucial for the recovery of valuable resources from saline textile wastewater. In this study, hollow fiber membranes were fabricated using the non-solvent-induced phase separation (NIPS) method and then improved with a dual-coating process to create effective nanofiltration (NF) membranes. First, hollow fiber substrates with Fe3+ were fabricated using NIPS. Subsequently, the inner surface of the membrane was coated with phytic acid (PA) and polyethyleneimine (PEI), which increased the thickness of the separation layer and reduced the size of the surface pores, thereby improving the separation efficiency. The loose NF membrane exhibited superior water permeance (pure water permeability of 280 L·m−2·h−1·bar−1) and, with dye rejection rates consistently exceeding 95%, also remarkable dye/salt selectivity (with separation factors of CR/NaCl: 64.08, CR/Na2SO4: 21.21, CBB/NaCl: 14.75, and CBB/Na2SO4: 10.74). The flux recovery of the membrane was over 80% for humic acid, and the membrane exhibited favorable stability under acidic and alkaline conditions, confirming its excellent antifouling and stability performance. In conclusion, this study presents a straightforward and effective approach for fabricating hollow fiber loose NF membranes, underscoring their potential for treating hypersaline wastewater and resource recovery.

Separations doi: 10.3390/separations13040119

Authors: Hancheng Mao Shengdong Wang Muyao Lu Haibei Wang Denggao Zhang

This study presents a combined process of sulfide precipitation followed by hydrogen peroxide leaching for rhenium recovery from copper smelting waste acid under ambient temperature and pressure. The process first removed copper through selective sulfide precipitation, then achieved co-precipitation of rhenium and arsenic to obtain a rhenium-rich precipitate. Subsequently, exploration of rhenium-containing precipitate leaching using H2O2 solution was conducted under isothermal conditions at 20 °C. The effects of H2O2 concentration, liquid-to-solid ratio, acidity, and leaching time rhenium extraction efficiency were examined systematically. The optimal leaching conditions were determined as: H2O2 concentration of 150 g/L, liquid-to-solid ratio of 5:1 mL/g, stirring speed of 350 r/min, and leaching time of 30 min. Under these conditions, the leaching conversions of rhenium and arsenic reached 96.0% and 93.8%, respectively. Through characterization of precipitate and leaching residue using ICP, SEM-EDS, XRD, and XPS analyses, the process and related reactions were elucidated. Results demonstrated that low-valence rhenium oxides and sulfides serve as the main reactive species during H2O2 leaching, whereas organic sulfur, high-valence oxides, and copper sulfide remained stable and resistant to leaching. Selective precipitation of copper effectively eliminated insoluble metal sulfides from rhenium-containing precipitates, thereby enabling efficient separation of rhenium under mild conditions.

Separations doi: 10.3390/separations13040118

Authors: Fang Li Yuping Fan Yuanpeng Fu Xiaomin Ma Xianshu Dong Yangge Zhu Wei Xiao Wenjie Fang

Fluorapatite is a typical phosphate rock resource. Fluorapatite tends to generate fine mud agglomeration, which induces dehydration challenges owing to its inherently fine particle size and negative surface charge. In this paper, phosphate tailings slurries from a phosphate mine in Hubei Province, China, were selected as the research object, and flocculation–dehydration experiments were conducted using anionic, cationic, and nonionic polyacrylamide (PAM) flocculants. The results show that the maximum settling velocity is 51 mm/s and the moisture content of filter cake is 41.54%, which were obtained when the unit consumption of cationic flocculant with molecular weight 12 million was 1000 g/t. The mechanism of sedimentation and dehydration was studied by infrared spectroscopy and a particle size analyzer. The results showed that polyacrylamide was effectively adsorbed on the mineral surface, and the size of flocs increased significantly. Finally, the mechanism of sedimentation and dehydration was proposed. It has important guiding significance for the efficient solid–liquid separation and water circulation of fluorapatite mineral processing wastewater.

Separations doi: 10.3390/separations13040117

Authors: Jun Zhang Ming Shao Minghan Zhou Lin Zhang Yingguang Zuo Lijun Wang Yadong Zhang

The paper utilizes the synergy of vibration and hot air flow to form a composite force field, and low-quality fine coal with viscous moisture is subjected to ash removal. The vibration signals of the bed surface at different positions are collected online using an accelerometer, and the dominant force affecting the vibration behavior of the bed is analyzed using signal time-domain analysis. By examining the impact of the synergy between vibration and airflow on the ash removal effect of low-quality, viscous moisture coal, the response of the drying and sorting behavior of low-quality fine coal to this synergy is elucidated. Based on the study of the experimental results of dehydration and ash removal of −6 + 1 mm fine coal, under the synergy of temperature and load force field, when the air flow temperature is 90 °C, v = 0.65 m/s, and f = 20 Hz, the collision force range between particles is 120 nN–370 N, which is different from that between particles. The liquid bridge force is large, which can achieve the fracture of liquid bridges between particles and strengthen the loose fluidization of particles. In addition, based on the study of the vibration characteristics of the bed surface at different positions, the vibration along the y-axis direction plays a dominant role in the density segregation behavior of the bed particles. With the increase in gas velocity and vibration frequency, the ash content of the selected clean coal exhibits a trend of first decreasing and then increasing. At the same time, the ash segregation degree initially increases and then decreases. Moreover, under the conditions of v = 0.65 m/s and f = 20 Hz, the separation effect of fine coal is the best. The separation accuracy E values of 1–6 mm without fine particles are 0.06 g/cm3, and the ash content of the clean coal is 12.55%.

Separations doi: 10.3390/separations13040116

Authors: Hideo Maruyama

Surface-modified waste scallop shells were investigated as a solid flocculant for removing suspended particles, and a light transmission method was examined as a simple approach for evaluating flocculation behavior. Kaolin suspensions (3, 5, 10 g/L, pH 6.95–7.05) were used as model wastewater. Temporal changes in transmitted light intensity were monitored using a white LED–sensor optical system after agitation of the suspension was stopped. The transmitted light intensity, I, was normalized by the intensity measured for particle-free water (I0), and an optical extinction index, A = −log10(I/I0), was used to describe the attenuation of light in the suspension. An apparent clarification rate (rate of change in optical extinction), v, was defined from the initial decrease in the optical extinction index and used as an operational kinetic parameter for comparing flocculation behavior under identical conditions. The results showed that the surface-modified scallop shell particles exhibited measurable flocculation activity toward kaolin suspensions, although the performance was lower than that of commercial polymer flocculants. The optical transmission method enabled continuous monitoring of the flocculation process and provided a practical index for comparing the flocculation performance of different materials.

Separations doi: 10.3390/separations13040115

Authors: Jing Chang Bianbian Guo Guoyu Bai Xinyuan Zhang Hang Zhang Wei Zhao Zhen Li

Intelligent dosing in coal slime water treatment remains a challenge due to the lack of real-time and solid hardware-based measurement of key microscopic parameters governing the settling process, particularly zeta potential. This study proposes a soft-sensor method using Sparrow Search Algorithm-optimized Extreme Learning Machine (SSA-ELM) to simultaneously predict four critical settling process parameters: settling velocity, supernatant turbidity, sediment layer height, and zeta potential. Key variables influencing the coal slime water settling process, including coal slime water concentration, fines content, water hardness, pH, and chemical dosage, were investigated, and the experimental data were used as inputs for the development of the prediction model. The prediction performance of the proposed SSA-ELM model was evaluated against standard ELM and SSA-optimized Back Propagation (BP) models. The results demonstrate that the SSA-ELM model achieved superior prediction accuracy for all parameters, with R2 values ranging from 0.95 to 0.98, while maintaining favorable computational efficiency. This study establishes a method for virtual measurement of zeta potential, providing a crucial data foundation for developing mechanism-driven, intelligent dosing systems aimed at precise intelligent control and reduced chemical consumption for coal preparation plants.

Separations doi: 10.3390/separations13040114

Authors: Haoqian Yan Guifeng Zhang Li Ma

This study aims to achieve the efficient preparation of sunflower calathide flavonoids (SCF) through optimized processes and to elucidate their composition and bioactivity. Total flavonoids were prepared by optimizing the ultra-high-pressure extraction (UHPE) process using a combination of single-factor experiments and response surface methodology, followed by purification and enrichment via macroporous resin. The components were identified with UPLC-QTOF-MS/MS technology, and their antioxidant activity and inhibitory capacity against xanthine oxidase (XOD) were systematically evaluated. The optimal extraction conditions were determined as follows: an extraction pressure of 290 MPa, a holding time of 8 min, an ethanol concentration of 67%, and a solid-to-liquid ratio of 1:14 g/mL. Under these conditions, the total flavonoid extraction yield reached 13.52 mg/g, which was further enriched to 16.74 mg/g after purification by macroporous resin. A total of 32 flavonoid compounds were identified, and the purified extract exhibited stronger free radical scavenging ability, total reducing power, ferric ion reducing activity, and XOD inhibitory effect compared to the unpurified extract. The combination of UHPE with macroporous resin separation technology effectively enriches SCF, and the resulting extract possesses both antioxidant and xanthine oxidase inhibitory activities, providing a theoretical basis and technical support for its industrial production and application.

Separations doi: 10.3390/separations13040113

Authors: Weinan Wang Xu Hou Jiahao Pan Wei Shi Xiaolu Ye

Flip-flow screens are widely used for the efficient separations of wet fine materials. To explore the separation characteristics of the particle and screen plate in the flip-flow screening process, a flip-flow plate impact experimental system was built. The experimental system was based on a spherical inertial measurement device and a semi-industrial flip-flow screen system. In this study, we first derive the impact mechanics equation of the flip-flow screen plate on the particle and analyze the influence of the main parameters on the maximum impact force. Subsequently, we investigated the kinematic characteristics of the particle impacted by the screen plate at different moving positions, the variation of the centerline acceleration mechanism, and determined the angular velocity in the collision process. Additionally, we further clarified the alteration in the rules of translational and rotational kinetic energy of the particles in the collision process. This study addresses a research gap in the phenomenological modelling of particulate screening process. At the same time, it provides theoretical support for the accurate control of the flip-flow screening process.

Separations doi: 10.3390/separations13040112

Authors: Qinhan Ye Pei Zhao Xuan Xia Yang Xiao Xinhong Qiu

Two mineral-based solid residues, namely coal gangue (CG) and phosphorus tailings (PT), two of the largest solid waste streams in the mining industry, were used as the sole metal feedstocks to fabricate a novel MgCaFeAl layered double hydroxide (LDH-GT) via a 700 °C calcination, acid leaching and hydrothermal coprecipitation route, with simultaneous synthesis of white carbon black from the reaction byproducts. Under optimized conditions (total metal load is 150 mg kg−1, LDH-GT dose is 0.09 g, pH from 6 to 7), the synthesized material achieved concurrent immobilization efficiencies of 76.28%, 99.96%, and 99.95% for Cr (VI), Cd (II) and Ni (II), respectively, within a 24 h reaction period. TCLP leachability decreased by 82 to 91% relative to the untreated soil. After three wetting, drying and freeze–thaw cycles, the leached concentrations of all three metals remained below 0.3 mg L−1, confirming excellent long-term stability. Mechanistic analyses revealed that Cr (VI) was mainly sequestered through interlayer anion exchange and surface complexation, whereas Cd (II) and Ni (II) were immobilized via isomorphic substitution into the LDH lattice, precipitation as carbonates, and incorporation into Fe/Mn oxides. A 7-day mung bean bioassay showed that LDH-GT amendment increased seed germination from 50% to 73%, enhanced root and shoot biomass by 1.1- to 1.6-fold, and decreased plant Cr, Cd, and Ni contents by over 80%. The 16S rRNA sequencing further demonstrated that LDH-GT reversed the decline in microbial α diversity induced by heavy metal stress, restored aerobic chemoheterotrophic and sulfur cycling functional guilds, and reduced pathogenic signatures. This study provides the demonstration of a waste-to-resource LDH that achieves efficient, durable remediation of multi-metal-contaminated soils, offering a scalable route for coupling solid waste valorization with in situ site restoration.

Separations doi: 10.3390/separations13040111

Authors: Xiaoxiao Cai Hao Lu

As an efficient solid–liquid separation device, the hydrocyclone is widely applied in various industrial fields such as coal preparation and oil impurity removal, and its classification performance directly determines the efficiency of industrial separation operations., As the core separation zone of the hydrocyclone, the cone segment, its structure and the number of cone angles directly affect the flow field distribution characteristics and particle classification performance of the hydrocyclone. To reveal the regulation mechanism of the combined cone angles on the classification performance of hydrocyclones, numerical analysis and experimental verification methods were adopted to investigate the internal flow field and classification performance of hydrocyclones under different cone angle combinations. The evolution laws of velocity field, pressure field, turbulence characteristics, and particle classification effect under different configurations were systematically explored. The results show that the basic characteristics of the core flow field of the hydrocyclone do not change essentially with the increase in the number of cone segments, but the amplitude, distribution, and stability of flow field parameters are significantly regulated. The three-cone configuration achieves the optimal flow field synergy effect: the amplitude of the high turbulence intensity zone is lower and concentrated near the central axis; the zero-velocity envelope surface is stably maintained at approximately 8 mm in the core separation zone; and the full axial fluctuation of the air core is gentle, which effectively inhibits random particle diffusion and flow pattern mixing. In terms of separation performance, the three-cone configuration exhibits the highest classification efficiency in the core range of sub-coarse particles (10~30 μm), with the cut size (approximately 17.5 μm) in a reasonable range, the steepness index reaching a peak value (approximately 0.55), and the pressure drop (approximately 1.8 × 105 Pa) and split ratio (2.8%) achieving synergistic optimization, balancing separation accuracy and energy consumption control. The single-cone configuration causes flow field disturbance due to the one-time contraction of the flow channel, while the four-cone configuration falls into the dilemma of “high pressure drop–marginal performance gain”, and neither achieves optimal performance. The regulation law of the number of cone segments revealed in this study provides a scientific basis for the structural optimization and engineering application of multi-cone hydrocyclones, and is of great significance for improving the particle classification efficiency in fields such as wastewater treatment and mineral processing.

Separations doi: 10.3390/separations13040110

Authors: Yan Fang Yi Nan Xijie Tian Junyu Zhang Xiaojuan Chen Juan Song Haizhen Liang Baiping Ma

Traditional Chinese prescriptions are characterized by complex chemical constituents and wide variations in constituent content, which pose a substantial challenge to their comprehensive characterization. As a classic traditional Chinese prescription known for its heat-clearing and detoxifying properties, Huangqintang Decoction (HQD) is composed of Scutellariae Radix, Paeoniae Radix Rubra, Glycyrrhizae Radix et Rhizoma, and Jujubae Fructus. In this study, we developed an off-line two-dimensional liquid chromatography that addressed the limitations of traditional analysis of unfractionated extracts, such as restricted peak capacity, which often obscured trace components. By coupling with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS), this study successfully performed rapid identification or characterization of the complete chemical profile of HQD. Notably, beyond high-throughput identification, this approach leveraged characteristic fragment ions and reversed-phase chromatographic behaviors to differentiate some isomers of flavonoid glycosides and triterpenoid saponins, demonstrating its depth in structural identification. Flavonoid glycoside isomers were distinguished by diagnostic neutral losses, while flavanones and chalcones were characterized by retro-Diels–Alder (RDA) and β-rearrangement, respectively. Isomers of triterpenoid saponins were inferred from aglycone-specific pathways alongside RDA cleavages. Ultimately, a total of 192 compounds were identified, including 88 flavonoids, 80 triterpenoids, 7 monoterpene glycosides, 3 fatty acid amides, 3 phenylethanoid glycosides, 4 coumarins, 3 saccharides, 1 organic acid, and 3 others. This study demonstrated that the off-line two-dimensional liquid chromatography analysis strategy significantly enhanced chromatographic resolution and expanded the coverage of trace components. It presented an effective strategy for comprehensive compound identification in complex traditional Chinese medicine prescriptions.

Separations doi: 10.3390/separations13040109

Authors: Panpan Chu Qihan Wang Fan Yang Guangpeng Chen Wangzhiyuan He Hao Pan Liting Fan Xiaojian Yang Jinpeng Shi Shaolong Wan

The selective removal of HCl from industrial HCl/SiF4 mixtures was investigated using a series of alcohol-based and deep eutectic solvents (DESs). Among them, glycerol (GL) exhibited superior selectivity for HCl despite a moderate total capacity. Absorption at 60 °C ensured stable operation with minimal foaming. Desorption analysis revealed that both HCl and SiF4 underwent partial irreversible absorption under N2 stripping, while staged vacuum desorption enabled efficient and selective recovery—SiF4 was fully removed at 70 °C and 6 kPa, followed by nearly complete HCl desorption at 90 °C. Cyclic tests confirmed excellent solvent stability and rapid regeneration, with complete desorption achieved within 10–15 min. A conceptual process was proposed based on these findings, demonstrating a practical and energy-efficient route for selective HCl recovery from acid–gas mixtures.

Separations doi: 10.3390/separations13040108

Authors: Xue Yu Zihan Zhai Qiangcheng Zeng Jiajia Chen Jiayi Wang Wei Zhao Jinling Liang Guoxiu Han

This study presents a novel, integrated membrane–resin hybrid platform for the high-efficiency purification of N-acetylneuraminic acid (sialic acid, NANA) from complex microbial fermentation broths. By synergistically combining four sequential stages—ceramic microfiltration (50 nm), ultrafiltration (3 kDa), nanofiltration (150 Da), and dual-resin purification (macroporous adsorption + cation-exchange)—the process achieves stepwise removal of cells, proteins, pigments, monovalent salts, and divalent metal ions without using organic solvents or high-salt buffers. Critically, each stage demonstrates high target recovery: 76.2% (CM), 67.3% (UF), and 77.5% (NF), with near-quantitative retention (>95%) during resin treatment due to NANA’s low hydrophobicity and electrostatic repulsion at pH 6.8. Following optimised acidification crystallisation (acetic acid dosage = 3 × concentrate volume; sialic acid concentrate concentration = 333.49 g/L), the final product reaches 97.9% purity with a crystalline yield of 78.6%. This scalable, green purification strategy eliminates major bottlenecks in downstream processing and enables industrial-scale production of pharmaceutical-grade sialic acid, with broad applicability to other high-value acidic biomolecules.

Separations doi: 10.3390/separations13040107

Authors: Shengbing Xiao Lixin Li

Mine water treatment remains a long-term challenge due to high suspended solids, wide particle size distributions, and inflow variability, all of which stress solid–liquid separation systems. Hydrocyclones and filtration often fail not from insufficient capacity, but from the inability to handle dynamic influent behavior. This review integrates existing studies and reinterprets mine water treatment as a system performance issue, focusing on maintaining operability under fluctuating conditions. Evidence shows that high-solids mine water behaves as a concentrated multiphase flow, where particle interactions and flow changes lead to gradual shifts in separation behavior. For example, hydrocyclone efficiency ranges from 85 to 95%, and pressure drop increases by 0.5–5 kPa/h under continuous operation. Wear, clogging, and flow redistribution develop together, impacting the operational window of integrated treatment units. Key gaps remain in system performance under fluctuating loads and reliable performance under high-solids loading. The complexity of these interactions often leads to significant operational risk and performance variability in real-world conditions. Future research should focus on dynamic control strategies, multi-stage pre-separation, and advanced filtration designs to enhance system performance, long-term stability, and adaptability in real mining environments. Emerging technologies and new system configurations may further improve efficiency and reduce operational failure risks under extreme conditions.

Separations doi: 10.3390/separations13040106

Authors: Cristiane Nunes da Silva Camilla Ribeiro Ferreira Bernardo Dias Ribeiro Filipe Smith Buarque

Spent coffee grounds (SCGs) are an abundant agro-industrial residue with high potential as a source of phenolic compounds and proteins. This study evaluated the extraction of these value-added fractions using hydrophilic and hydrophobic eutectic solvents, applied either alone or combined with enzyme-assisted extraction. A total of 31 hydrophobic eutectic solvents (HESs), nine hydrophilic deep eutectic solvents (DESs), and five conventional solvents were screened for phenolic recovery. Extraction performance was strongly formulation-dependent, with hydrophobic systems showing the highest phenolic yields. HES 4 (camphor:oleic acid) was the best-performing solvent, reaching 1279.49 ± 2.31 mg GAE L−1, followed by borneol:oleic acid (1133.92 ± 5.29 mg GAE L−1). Enzyme addition did not enhance phenolic extraction; the highest values under enzymatic conditions were 896.12 ± 4.80 mg GAE L−1 for HES 4 + Cellic® CTec2 and 819.84 ± 2.66 mg GAE L−1 for HES 4 + Viscozyme®. In contrast, protein extraction increased remarkably with enzyme supplementation, particularly with Cellic® CTec2. The highest protein recovery was obtained with HES 4 + Cellic® CTec2 (1608.74 ± 3.32 mg·L−1), compared with 506.37 ± 5.20 mg·L−1 for neat HES 4. In general, neat HESs were more suitable for phenolic recovery, whereas HESs combined with Cellic® CTec2 were more effective for protein extraction.

Separations doi: 10.3390/separations13040105

Authors: Xiu Wang Xiao-Juan Chen Qing Sun Juan Song Hai-Zhen Liang Bai-Ping Ma

Fufang Yinhua Jiedu Granules (FFYHG) is usually applied to treat influenza and the common cold. However, there is no available report concerning the effects of chemical constituents in FFYHG on antiviral activity. In our study, four new terpenoid derivatives (1–4) and seventeen known compounds were isolated from FFYHG. Their structures and absolute configurations were determined by various techniques, including high-resolution mass spectrometry analysis, 1/2-dimensional (1D/2D) nuclear magnetic resonance (NMR) analysis, comparative electronic circular dichroism (ECD) studies (experiment vs. calculation), and acid hydrolysis. In addition, the inhibitory effects of twenty-one isolated compounds against influenza A viruses (H1N1) including A/California/07/2009 (CA07) and A/WSN/1933 (WSN) strains were evaluated in vitro, and compound 4 exhibited a moderate inhibitory effect on CA07 strain, with a half maximal inhibitory concentration (IC50) value of 37.10 ± 1.35 μM. This study enhanced the understanding of the active ingredients in FFYHG against influenza virus, providing a foundation for further research on the material basis and quality control of FFYHG.

Separations doi: 10.3390/separations13040104

Authors: Tingting Ren Hongxiang Zhu Zongqiang Zhu Jian Tan Qiqi Qin

In this work, iron–phosphorus-based composite biochar (FPBC) was prepared by modification with the leachate of spent LiFePO4 batteries. The effects of solution pH, dosage, adsorption time, initial concentration, and temperature on the adsorption performance of FPBC were investigated by batch adsorption experiments with Pb(II) and Sb(III) as the target pollutants, and the adsorption mechanism was explored using SEM, BET, XPS, FTIR and XRD characterization. The results indicated that as the initial pH of the solution increased, the removal efficiency of FPBC for Pb(II) gradually increased, while the removal efficiency for Sb(III) remained largely unchanged. The removal of Pb(II) and Sb(III) by FPBC fitted the pseudo-second-order kinetic model and the three-step intraparticle diffusion model, indicating that their removal was primarily controlled by chemical adsorption. Isothermal adsorption studies revealed that FPBC adsorption of Pb(II) better fitted the Langmuir and D-R models, suggesting a monolayer-dominated adsorption process. In contrast, adsorption of Sb(III) fitted the Langmuir, Freundlich, and Temkin models, suggesting a combination of monolayer and multilayer adsorption characteristics. The maximum adsorption capacities of FPBC for Pb(II) and Sb(III) were 312.54 mg·g−1 and 219.20 mg·g−1 at 30 °C, which were approximately 12.85 and 3.37 times those of commercial corn stalk biochar (BC). Thermodynamic analysis confirmed that the removal of Pb(II) and Sb(III) by FPBC was a spontaneous and endothermic process. In addition, FPBC demonstrated strong selective adsorption of Pb(II) in the binary co-adsorption system of Pb(II) and Sb(III). Mechanism studies indicated that Pb(II) removal primarily occurred through co-precipitation, complexation, ion exchange, and electrostatic adsorption, while Sb(III) was mainly adsorbed by FPBC via redox reactions and complexation. Therefore, this work not only provides a low-cost, high-performance adsorbent for the remediation of water contaminated with Pb(II) and Sb(III), but also opens up new avenues for the resource recovery of the leachate of spent LiFePO4 batteries.

Separations doi: 10.3390/separations13040103

Authors: Mara Junqueira Carneiro Alexandre Augusto Borghi Guilherme Perez Pinheiro Ana Lucia Tasca Gois Ruiz Daniela Mizobutti Elaine Minatel Lisieux Santana Juliao Svetlana Ignatova Peter Hewitson Alexandra Christine Helena Frankland Sawaya

The chemical composition of natural products is complex and the investigation of bioactivities of compounds of interest demands their isolation. S. terebinthifolia Raddi is a tree belonging to the Anacardiaceae family and is used in Brazilian folk medicine; its fruit (pink peppers) are used in cooking and its bark in phytomedicine. Extracts of other parts of this plant contain a plethora of components and merit further studies. Countercurrent chromatography (CCC) is frequently employed with natural products due to the high sample recovery rate. The objective of this work was to determine the best solvent system (SS) to fraction the ethanol extracts of leaves, flowers and fruit of Schinus terebinthifolia by CCC and isolate compounds of interest and elucidate their structures through nuclear magnetic resonance (NMR) and mass spectrometry (MS). In addition, antiproliferative, potential cell regeneration and antioxidant activities of the fractions of interest were evaluated. In the present work, three compounds were isolated; two were identified as anacardic acids [(6-(8′, 11′-heptadecadienyl)-salicylic acid and 6-(8′-heptadecenyl)-salicylic acid], as well as (Z)-masticadienoic acid. These compounds showed antiproliferative and potential cell regeneration activities as well as varying degrees of antioxidant capacity. Although these compounds present potential therapeutic activity, more studies are necessary to confirm their safety.

Separations doi: 10.3390/separations13040102

Authors: Luca Farina Gessica Cortese Daniela Pietrogiacomi Maria Cristina Campa Silvano Tosti

Plasma Enhancement Gases (PEGs) are a set of gaseous elements studied for converting plasma thermal energy and mitigating the heat load on the plasma-facing components of a tokamak fusion power plant. In particular, PEG separation is part of the Plasma Exhaust Processing System of EU-DEMO. This work addresses issues related to the purification of Deuterium-Tritium fusion fuel, introducing ceramic membranes having a low specific area to process and purify unburned streams throughout the fuel cycle. A commercial microporous mono-channel α-Alumina membrane was considered for the evaluation of its efficacy in separating binary mixtures of H2 with a PEG (Ar and N2), D2, or He. Several tests were carried out, feeding equimolar streams of H2-Ar, H2-N2, D2-Ar, and He-Ar, and the separation factor (SF) of the aforementioned binary mixtures was experimentally assessed. Finally, based on the results from the experimental campaign, the separation factors of several gas mixtures that had not been experimentally investigated were theoretically calculated and proposed.

Separations doi: 10.3390/separations13030101

Authors: Jiawei Lin Jue Kou Chunbao Sun Xiaojin Wen Hongda Xu

Rare earth elements (REEs), as significant associated resources in sedimentary phosphate deposits, are commonly processed via the conventional hydrochloric acid wet-process phosphoric acid route (IMI process). In this method, phosphate and rare earth elements are typically leached simultaneously, which subsequently complicates their separation. In this study, a dolomitic rare earth-bearing phosphate concentrate from the Zhijin region of Guizhou Province was selected as the research subject. A stepwise phosphorus-prioritized leaching process was proposed, whereby precise regulation of hydrochloric acid dosage and reaction temperature enabled the preferential leaching of phosphorus (91.27%) and the directed enrichment of rare earth elements in the leaching residue (enrichment ratio of 4.7), thereby achieving efficient phosphorus–rare earth separation at the source. Subsequent process mineralogical analyses of the phosphate concentrate and the leaching residue revealed that rare earth elements occur in fluorapatite predominantly through isomorphic substitution. Following preferential phosphorus leaching, the residual Ca combines with F to form CaF2, while rare earth elements become concentrated within the leaching residue. Finally, kinetic investigations and response surface analyses demonstrated that the preferential phosphorus leaching process is governed by diffusion through the solid product layer. Among the influencing factors, hydrochloric acid dosage (A), leaching temperature (C), and the interactions between leaching time and the solid–liquid ratio (B, D) were identified as the most significant parameters affecting phosphorus leaching efficiency. This study elucidates, from a mechanistic perspective, the governing principles of phosphorus dissolution and rare earth enrichment within the hydrochloric acid preferential leaching system, thereby providing important theoretical support and technical guidance for simultaneously achieving efficient phosphorus extraction and targeted rare earth enrichment within the hydrochloric acid wet-process phosphoric acid production route.

Separations doi: 10.3390/separations13030100

Authors: Xin Shen Jules Thibault

Adsorption is a widely employed separation technique valued for its low energy requirements and its applicability to diverse processes, including air separation, water purification, chromatographic analysis, wastewater treatment, and protein immobilization on biomaterials. Industrial adsorption–desorption cycles are typically carried out in parallel packed-bed columns. The accurate design and optimization of these columns rely on experimental breakthrough curves. These curves provide essential information on adsorption capacity and mass-transfer kinetics. In this study, five modelling approaches, based on instantaneous adsorption, non-instantaneous adsorption, Fickian diffusion, and anomalous diffusion, were evaluated for their ability to predict breakthrough behaviour during the adsorption of butanol on activated carbon. The first four models were formulated using conventional partial differential equations of varying complexity, whereas the fifth model incorporated anomalous diffusion through fractional-order differential equations. The results indicate that model performance depended strongly on the adsorbent type: certain models provided superior predictions for one activated carbon, while different models were more accurate for the other.

Separations doi: 10.3390/separations13030099

Authors: Jing Chang Hang Zhao Shizhen Liang Xihao Feng Jia Xue Wei Zhao

High-ash coal slime water, characterized by its stable colloidal suspension of fine kaolinite particles, poses a significant challenge in the coal preparation industry because it is hard to achieve efficient solid–liquid separation. While traditional coagulants and flocculants often suffer from limited bridging capabilities and distinct pH sensitivity, novel molecular architectures offer potential solutions. In this study, a star-shaped inorganic–organic hybrid flocculant (Al-PAM) was synthesized via in situ polymerization. Its flocculation performance and interfacial adsorption mechanism on the specifically targeted aluminol basal plane of kaolinite were systematically investigated and compared with Polyaluminum Chloride (PAC), Non-ionic Polyacrylamide (NPAM), and their combination (PAC + NPAM). Settling tests revealed that Al-PAM exhibited superior performance at a significantly lower dosage (10 mg∙L−1) compared to the PAC + NPAM binary reagent system. It achieved a rapid initial settling velocity and reduced the supernatant turbidity to 48.45 NTU, while maintaining a near-neutral pH favorable for water recycling. Furthermore, Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring confirmed that Al-PAM forms a thick, viscoelastic, and irreversible adsorption layer on the Al2O3 substrate. The dissipation shifts (ΔD) revealed that the star-shaped architecture promotes distinct bridging and electrostatic adsorption, overcoming the limitation of linear polymers. This work elucidates the specific contribution of the alumina-surface interaction with flocculants and proposes an efficient strategy for treating refractory coal slime water.

Separations doi: 10.3390/separations13030098

Authors: Gang Tian Yihang Tian Shiping Cheng Cong Yang Guoxu He

Macroporous adsorption resins (MARs) are widely used for preparative-scale flavonoid purification, yet rational resin selection remains difficult because flavonoids differ substantially in hydrophobicity, hydrogen-bonding capacity, molecular size, and planarity. This review reorganizes the available literature into a structure-guided and data-supported selection aid rather than a fully predictive model. A systematic search of Web of Science, Scopus, PubMed, and CNKI (January 2000 to February 2026) identified 55 studies for qualitative synthesis. Because many reports describe total flavonoids or mixed extracts rather than explicit single-compound adsorption data, only the subset with sufficiently clear compound-level or narrowly interpretable adsorption information was used for cautious comparative interpretation. Across the compiled evidence, non-polar resins generally favored less polar aglycones and methoxylated flavonoids, whereas medium-polar and polar resins more often performed well for glycosylated or more hydrophilic targets. On this basis, flavonoids were organized into four operational classes linked to recommended resin polarity, indicative adsorption capacity ranges, and typical ethanol-elution windows. A retrospective comparison with independent literature cases suggests practical value for initial resin prioritization, but the framework should be interpreted primarily as a heuristic, trend-based guide rather than as a strictly predictive model, because mixed-matrix effects, pore accessibility, and competitive adsorption can override simple polarity matching. A generalized operating window for adsorption and desorption is also summarized. Overall, this review provides a mechanism-informed starting point for resin screening while making explicit the conditions under which case-specific experiments remain necessary.

Separations doi: 10.3390/separations13030097

Authors: Li Yao Kuan Xu Linfang Zhang Xiaodong Wu

Ammonium bisulfate (ABS) fouling in air preheaters has become a critical challenge restricting the safe and efficient operation of coal-fired units. Optimizing the flow field of the outlet of the upstream SCR system is a potentially effective path to mitigate ABS fouling. In this work, CFD simulations were conducted on the SCR De-NOx system and its succeeding flue ducts connected to the air preheater. The simulation results of the original design show that a significant velocity deviation exists at the inlet of the air preheater (with the CV1 up to 53.2%), with a portion of the flue gas adhering to the walls, which could induce ABS fouling in the low-temperature region. By adding flow guide plates into the flue duct, the flow uniformity before the air preheater was expected to be effectively improved. Notably, considering the deposition characteristics of ABS and the operating characteristics of the rotary air preheater, this study proposed a novel evaluation indicator, radial variance coefficient (CV2), which focuses on the velocity uniformity based on the annular sector unit, to indicate the risk of ABS deposition. The influence on velocity uniformity of different flow guide plate layouts was analyzed. Based on the multiple evaluation metrics including pressure drop and flow uniformity, the optimal layout scheme was then selected. After optimization, the radial variance coefficient decreased from 30.7% to 11.7%, with the pressure drop slightly increased from 50 Pa to 80 Pa. This study could help to reduce unit failure frequency and support efficient operation of coal-fired power plants.

Separations doi: 10.3390/separations13030096

Authors: Xinyu Dong Yu Zhang Xinyi Zhang Yaping Xu Haitao Zhao Nan Jiang Lijun Meng Shengyang Zheng

To efficiently remove oxytetracycline (OTC) pollution from water bodies, this study utilized fava bean straw as a precursor to synthesize iron-nitrogen (Fe/N) co-doped biochar via pyrolysis. By regulating the synthesis ratio of iron and nitrogen, the material’s adsorption performance was optimized. The adsorption characteristics and mechanisms of OTC were systematically investigated. The findings reveal that when the proportion of iron to nitrogen is set at 1:3, the adsorption efficacy reaches its peak. Moreover, this material demonstrates outstanding reusability characteristics. The outcomes of kinetic fitting suggest that the adsorption procedure adheres to the pseudo-second-order kinetic model (R2 = 0.967), primarily characterized by chemisorption. The isothermal adsorption data better fit the Langmuir model (R2 = 0.9984), with a theoretically attainable upper-limit adsorption capacity reaching 666.13 mg/g. This signifies the occurrence of monolayer adsorption, while the adsorption procedure constitutes an endothermic reaction. Based on characterization and mechanistic analysis, it can be concluded that the adsorption mechanism of Fe1N3KBC on OTC mainly involves π-π stacking interactions and chelation reactions. The Fe/N co-doped biochar prepared in this present research features readily available raw materials and a simple preparation process, combining high adsorption efficiency with excellent stability. It provides a novel technical paradigm for developing environmentally friendly adsorbents to address antibiotic pollution in water bodies.

Separations doi: 10.3390/separations13030095

Authors: Linhe Sun Ying Yang Jianguo Yu

This paper reports the chiral separation of menthol enantiomers using the VARICOL process to improve productivity. Amylose 3,5-dimethylphenylcarbamate coated on silica gel was employed as the chiral stationary phase, and n-hexane/2-propanol (95/5, v/v) was used as the eluent. To design and optimize the VARICOL process, a linear driving-force model was developed to predict the separation performance. Separation regions of the conventional simulated moving bed (SMB) and VARICOL processes were evaluated and compared. It was found that, under an outlet purity requirement of 95.0%, the five-column VARICOL process has a separation region comparable to that of the six-column conventional SMB process. As an illustrative example, a five-column VARICOL unit and a six-column conventional SMB unit, both operating under the same conditions, were employed to resolve the menthol racemate. Purities for both the extract and raffinate were above 95.0%, and a productivity of 0.400 gracemate/(LCSP∙min) and a solvent consumption of 0.355 L/gracemate were achieved in the VARICOL process. Productivity increased by 20% while solvent consumption maintained relative to the conventional SMB process, though product purities decreased slightly.

Separations doi: 10.3390/separations13030094

Authors: Khadejah D. Otaif

Skin-whitening products (SWPs) are widely used, yet many contain prohibited or misdeclared depigmenting agents posing safety concerns. This study developed and validated a sensitive and reliable HPLC-DAD method for the simultaneous determination of hydroquinone (HQ), salicylic acid (SAL), and niacinamide (NIC) in commercial and homemade SWPs. Validation followed ICH Q2(R1), demonstrating good specificity, linearity (R2 > 0.9999), method precision (%RSD < 2%), and LOD/LOQ values of 0.2 and 0.7 µg/mL for all analytes. Recoveries of 97.48–99.83% for HQ, 99.37–101.26% for NIC, and 83.04–95.38% for SAL were also obtained. Analysis of 51 products revealed major discrepancies between declared and measured contents. HQ was detected in 18.60% of commercial samples despite its prohibition in OTC cosmetic formulations; none of the SAL-containing products matched their labels, and NIC appeared in 25.58% of samples, with only one sample compliant with its declared content. Homemade products showed undeclared HQ in 62.50% of samples, 25% of samples exceeded the 2% permitted SAL limit, and unregulated multi-ingredient combinations. Risk assessment showed all HQ-containing commercial products and several homemade formulations posed unacceptable systemic exposure risks (MoS < 100). Overall, the proposed method provides a practical and accessible approach for routine quality control and market surveillance of cosmetic products.

Separations doi: 10.3390/separations13030093

Authors: Changryeol Oh Dongkeon Kim Suhan Kim

This study investigates how membrane transport characteristics affect permeate quality in a 2-pass reverse osmosis (RO) system for ultrapure water (UPW) production. Unlike conventional RO, UPW-RO operates in an ultra-low concentration range. Seven commercial 4-inch RO membrane modules spanning a wide range of water (A) and salt (B) permeability coefficients were evaluated under various second-pass RO feed concentrations (specifically, total dissolved solids (TDS) and total organic carbon (TOC)). Second-pass RO permeate TDS remained almost constant regardless of membrane specifications, whereas the permeate TOC was strongly membrane-dependent. RO permeates from high-permeability membranes showed significantly higher TOC than those from high-selectivity membranes. The experiments also revealed that a high-permeability membrane configuration for both RO passes resulted in excessive TOC leakage, while a high-selectivity membrane configuration mitigated TOC passage at the cost of a high operating pressure requirement. A combination of a high-permeability membrane (the first pass) and a high-selectivity membrane (the second pass) could achieve an acceptable TOC passage with a moderate operating pressure requirement in UPW-RO systems.

Separations doi: 10.3390/separations13030092

Authors: Naoyuki Iwata Kazunari Fukumoto Mitsuharu Uchino

5-aminolevulinic acid (5-ALA) affords various positive health effects, including benefits for conditions such as diabetes. Biological fermentation holds potential for efficiently mass-producing biomolecules, including 5-ALA, yet it generally results in a mixture of target molecules and impurities, including byproducts. Pyrazine-2,5-dipropionic acid (PY), a dimer of 5-ALA, can easily form in 5-ALA production and is one of its major impurities. In this study, we developed an integrated purification process for 5-aminolevulinic acid phosphate (5-ALAP) produced via biological fermentation. The process consists of 16 stages, including impurity removal (ion-exchange resins) and crystallization. Three types of ion-exchange resin (IER) columns were combined to remove impurities such as byproducts and pigment. Comprehensive condition setting for crystallization was carried out to reduce the amount of residual poor solvent in the 5-ALAP crystals. The obtained crystals contained significantly fewer impurities (<0.05% vs. 5-ALAP), such as PY, compared with their commercially available counterparts. The residual poor solvent in the 5-ALAP crystals was reduced to below 1000 ppm under the crystallization conditions. We confirmed the high scalability of the purification method developed in this study. Therefore, this article provides an industrially applicable purification process for fermentatively produced 5-ALA.

Separations doi: 10.3390/separations13030091

Authors: Yuxuan Bai Huabing Zhu Haijun Bi Yigeng Huang

Traditional lithium-ion battery recycling relies mainly on pyrolysis or chemical leaching to separate current collectors from electrode materials, inevitably resulting in secondary pollution. In contrast, eddy current separation (ECS) applied to crushed lithium-ion battery residues can substantially reduce the introduction of contaminants while minimizing material losses. However, the heterogeneous composition and diverse surface characteristics of crushed battery products, together with the conductivity degradation of electrode materials after long-term use, make conventional empirical particle–trajectory correlations inadequate for accurate optimization of ECS operating parameters. In addition, the coupling between process parameters and the resultant forces acting on conductive particles, as well as the associated separation trajectories, remain insufficiently understood, which severely limits process controllability. A force–trajectory model was therefore developed for spent current collectors and conductivity-degraded LiFePO4 to describe their particle dynamics in an alternating magnetic field. The results demonstrate that the trajectory of LiFePO4 is very similar to that of non-conductive materials, thereby facilitating its effective separation from metallic components in battery scrap. Eddy current separation experiments further confirm the accuracy of the model predictions with respect to separation trajectories and the influence of key process parameters. On this basis, optimization of the operating parameters increased the separation efficiency of the cathode material to above 95.1%. The clarified ECS mechanism for current collectors and electrode materials provides new insights into the mechanical pre-sorting and mechanistic understanding of lithium-ion battery fragments, thereby contributing to reductions in contaminant introduction during battery material recycling.

Separations doi: 10.3390/separations13030090

Authors: Li Shang Yiyang Zhang Miao Long

The extraction of functional organic compounds from natural products has become an important focus of current research. Citrus fruits are among the most widely produced fruits worldwide and have attracted increasing attention because of their pleasant flavor and rich content of bioactive compounds. Hesperidin, the focus of this review, is a representative flavonoid glycoside that is abundant in citrus fruits and their processing by-products. Owing to its unique molecular structure and physicochemical properties, hesperidin frequently coexists with structurally similar flavonoids. This similarity makes its separation and purification particularly challenging. Although many studies have reported different methods for the extraction and purification of hesperidin, most of them concentrate on individual techniques. Systematic analyses of how upstream extraction strategies affect downstream separation efficiency are still limited. In this review, separation strategies for hesperidin are systematically discussed, covering the entire process from extraction to downstream purification. The focus shifts from isolated separation methods to a strategy-oriented design. Special attention is given to how different extraction approaches influence matrix complexity, and, consequently, the difficulty of subsequent separation steps. Downstream separation technologies, including adsorption, liquid–liquid partitioning, crystallization, and chromatography, are compared from the perspectives of separation mechanisms and process integration. Based on a comparative analysis of crystallization, phase partitioning, membrane processing, adsorption, and chromatographic techniques, this review discusses the typical process roles of different separation strategies. Solubility-driven crystallization and membrane-based clarification are identified as more suitable for large-scale processing, whereas adsorption and chromatography are more appropriate as enrichment and polishing steps, respectively. In addition, key control points for green extraction–separation integration are identified, including solvent recyclability, matrix complexity control, and early-stage load reduction. This work aims to provide a practical reference for the sustainable and scalable separation of flavonoid glycosides from citrus by-products.

Separations doi: 10.3390/separations13030089

Authors: Jiahao Li Jibiao Han Han Yang Guozhen Wang Kuo Liu Lang Liu Yong Li Qingfeng Xiong Junmei Guo Bin Yang Haigang Dong

Platinum group metals (PGMs) are strategic metals, and recycling PGMs in spent automobile exhaust catalysts (SACs) is a key path to alleviate the contradiction between resource supply and demand. This paper proposes a new Cu-Ni capture process and conducts research on the recovery of PGMs from SACs. Through the binary phase diagram analysis of Cu, Ni and PGMs and the thermodynamic calculation of the system reduction reaction, the feasibility of this technology was theoretically confirmed. Experimental results show that under the conditions of a temperature of 1450 °C, a holding time of 90 min, a Cu-Ni ratio of 1:1, and a basicity of 0.58, the recovery rates of Pt, Pd, and Rh reached 99.2%, 99.34%, and 98.48% respectively. Combined with orthogonal experiments, it was verified that temperature is the most influential factor on the recovery rate, and the four-stage capture mechanism of “initial diffusion—droplet aggregation—sedimentation and wetting—slag–metal separation” was clarified. This process reduces the melting temperature and provides new technology for green and efficient recycling of PGMs.

Separations doi: 10.3390/separations13030088

Authors: Gangqiang Zhao Ke Li Fengyuan Cui Shaoyu Yao Yadong Zhang Zongsheng Sun

Coal slime, typically with particle sizes below 1 mm, is difficult to utilize directly and is frequently associated with energy loss and environmental burden. This study comparatively investigates hot–air drying and transient steam flash drying for the dehydration and upgrading of filter–pressed coal slime. In hot–air drying, elevated temperature and reduced particle size markedly accelerate the drying rate, and the apparent activation energy ranges from 18.39 to 20.96 kJ·mol−1 for different particle sizes. For steam flash drying, the influences of steam pressure, particle size, and holding time on moisture–removal efficiency and physicochemical structure are evaluated. The dehydration performance is enhanced by higher steam pressure and larger particle size, reducing the moisture content of the coal slime from 38% to 20%, with approximately 80% of the total water removed during the transient depressurization stage. Structural analyses reveal partial decomposition of oxygen–containing functional groups and mesopore contraction after flash treatment. Compared with hot–air drying, steam flash drying achieves shorter processing time and lower specific energy consumption. These findings indicate that steam flash drying is governed by a pressure–induced phase transition and enhanced thermodynamic driving force, providing an intensified pathway for the efficient upgrading of high–moisture coal slime.

Separations doi: 10.3390/separations13030087

Authors: Yuejiao Yang Yingjie Guo Guanglin Huang Qiongwei Yu

A simple, rapid, and cost-effective method for the determination of benzo[a]pyrene (BaP) in edible oil was developed and validated. Nickel oxide-deposited silica (SiO2@NiO) was employed as a solid-phase extraction (SPE) adsorbent for the extraction of BaP from edible oil, followed by high-performance liquid chromatography–diode array detector (HPLC-DAD) analysis of BaP. The edible oil was diluted with n-hexane and directly loaded to SiO2@NiO for SPE. The n-hexane was also used to clean the fat-soluble interference substance in the edible oil, and BaP was selectively captured using SiO2@NiO through the electron donor–acceptor interaction. The SPE conditions, including the amount of adsorbent, volume of washing solvent, and type and volume of desorption solvent, were optimized. This SiO2@NiO-based SPE coupled with the HPLC-DAD method demonstrated good linearity within a BaP concentration range of 6–1875 ng/g in edible oils, with a limit of detection of 1.3 ng/g, spiked recovery of 97.4–105.1%, and relative standard deviation (RSD) of <3.0%. The method was applied to the analysis of BaP in 11 real oil samples (soybean oil, olive oil, corn germ oil, flaxseed oil, walnut oil, sunflower kernel oil, peanut oil, unrefined oil, and high-temperature frying oil), and the results show that the unrefined oil and high-temperature frying oil were at risk of BaP exceeding acceptable level.

Separations doi: 10.3390/separations13030086

Authors: Yuzhe Hua Wenli Liu Qiming Zhuo

China’s coking coal resources are scarce, and maximizing the recycling of these resources is the primary objective of coal processing and utilization. The embedding features of inorganic minerals within coking middling coal resources are an inherent factor influencing their liberation and separation efficiency. However, current research lacks a systematic investigation into how the embedding features of inorganic minerals in coking middling coal affect their liberation characteristics and flotation separation performance. This study examines three Chinese coking middling coal samples with distinct embedding features. Based on quantitative characterization of inorganic mineral embedding, grinding tests with varying durations and flotation separation tests on post-grinding products were conducted. Liberation and separation efficiencies were evaluated to explore the influence of inorganic mineral embedding on liberation degree and the subsequent impact of the liberation degree on flotation performance. The results indicate that the three coking middling coal samples with different embedding features exhibit significant differences in the dissociation behavior between inorganic minerals and organic matter. The particle size (D) of inorganic mineral phases is the primary factor influencing the liberation degree of inorganic minerals, while the complexity of intergrowth between inorganic minerals and organic matter (CIG) is a secondary factor. The CIG is the primary factor affecting the liberation of organic matter. As the liberation of inorganic minerals and organic matter increases, the separation efficiency improves for the Liuwan middling coal samples, whereas it deteriorates for the Shaqu and Changzhi samples.

Separations doi: 10.3390/separations13030085

Authors: Ying Wei Yuqiong Li Yingchao Liu Yuxin Guo Caiyun Li Wanglin Yang

Fluorite (CaF2) and barite (BaSO4) commonly occur together in the same deposits. Due to their similar surface chemical properties, their flotation separation is often challenging. In flotation pulps, dissolved metal ions can further interfere with separation and exert a pronounced influence on the flotation behavior of these minerals. This study investigated the effects of metal ions frequently encountered in industrial pulps (Fe3+, Al3+, Mg2+, Ca2+, and Zn2+) on the floatability of fluorite and barite in a sodium oleate (NaOL) collector system. The aims were to clarify how metal ions affect flotation behavior and to evaluate the feasibility of enhancing fluorite–barite separation via metal-ion regulation. Flotation results showed that, in the NaOL system, the largest floatability difference between fluorite and barite occurred at pH 10. Al3+ exhibited the strongest depression on barite while only weakly affecting fluorite flotation. Fe3+ and Mg2+ caused slight depression of barite, whereas Ca2+ and high concentrations of Zn2+ (>20 mg/L) promoted barite flotation. Overall, these metal ions had little influence on fluorite flotation. Adsorption measurements indicated that Al3+ reduced NaOL adsorption by more than 40% and decreased the contact angle from 35.6° to 23.1°, resulting in a sharp loss of surface hydrophobicity. ICP adsorption tests revealed that Al3+ showed the highest uptake on barite surfaces. Density functional theory (DFT) calculations further confirmed that surface SO42− groups on barite form strong chemisorption with hydrolyzed Al species (adsorption energy: −436.19 kJ/mol), whereas only weak physisorption occurs on hydroxylated fluorite surfaces (adsorption energy: −43.73 kJ/mol). This study provides insights into the flotation separation of non-metallic minerals dominated by polar ionic bonding and offers practical guidance for efficient fluorite–barite separation under complex ionic environments.

Separations doi: 10.3390/separations13030084

Authors: Thomas A. Brettell

Green Analytical Chemistry (GAC) provides a framework for reducing hazardous reagents, energy consumption, and waste. The topic has gained momentum across many chemical industries over the past 25 years; however, progress in implementing sustainable methods and conducting greenness assessments within forensic laboratories has been comparatively slow. The purpose of this review is to highlight green approaches to analytical separation methods, including greenness assessment metrics, that have been reported in the literature for forensic chemistry and toxicology applications and to raise awareness of GAC in the forensic field. Recent scientific literature highlights promising advances in greener sample preparation and chromatographic approaches, particularly in forensic toxicology and seized-drug analysis. Emerging trends include the use of green solvents, bio-based and deep eutectic solvent systems, and the rapid expansion of microextraction techniques such as SPME, LPME, MEPS, FPSE, and DLLME, which reduce solvent volumes, minimize waste, and support higher-throughput workflows. Parallel developments in portable and miniaturized chromatographic instrumentation such as miniaturized LC–MS systems with increased detection specificity and Lab-on-a-Chip applications show promise for in situ measurements in the field. Ambient ionization mass spectrometry—in particular, DESI and DART—has had a major impact on forensic chemistry by providing tools for the rapid and direct analysis of chemical compounds in complex matrices with little or no sample preparation. Greenness assessment tools—including AGREE, AGREEprep, Eco-Scale, GAPI, and BAGI—are increasingly applied to evaluate analytical methods in forensic chemistry and toxicology, including those used for novel psychoactive substances. Although many green methodologies are well documented, their routine implementation remains limited. The continued integration of green solvents, microextractions, portable instrumentation, and standardized greenness metrics will be essential for advancing sustainable forensic separations.

Separations doi: 10.3390/separations13030083

Authors: Ruiling Du Xiaoya Li Shuai Wang

With ongoing development in the process industries, the accumulation of industrial inorganic solid wastes (IISWs) has become increasingly significant. IISWs are characterized by large volume and toxicity and pose challenges in treatment and control. IISWs from chemical processes mainly include red mud (RM), zinc slag, lithium slag (LS), electrolytic manganese residue (EMR), phosphogypsum (PG), water treatment sludge (WTS), sewage sludge, blast furnace slag (BFS), steel slag (SS), coal fly ash (CFA), coal gasification slag (CGS), copper smelting slag (CSS), and lead smelting slag (LSS). Having been chemically processed, they exhibit complex compositions that pose challenges for further utilization. In this paper, we comprehensively review the preparation of adsorbents from IISWs as raw materials, the applications of IISW-derived adsorbents, and their adsorption mechanisms. The obtained adsorbents include modified IISWs, zeolites, porous ceramics, and composite and hybrid adsorbents. The adsorption mechanisms, such as van der Waals forces, electrostatic interactions, and π–π interactions, contribute to the rapid adsorption kinetics and high adsorption capacity observed in these adsorbents.

Separations doi: 10.3390/separations13030082

Authors: Aping Gan Tingting Zou Huanlu Song Shuxin Zhao Lanlan Zhang Zejie Ling

This study investigated the aroma characteristics of three grades of raw tea leaves and their corresponding jasmine tea products from Guangxi, China. Aromatic profiles of jasmine tea varieties were analysed using two-dimensional gas chromatography-olfactory-mass spectrometry (GC×GC-O-MS), stir bar sorptive extraction (SBSE), and descriptive sensory evaluation. Chemometric methods were applied to compare sensory scores with instrumental data. Volatile compound concentrations and relative odour activity values (r-OAVs) were calculated. The results indicated significant differences in base tea leaf quality: high-grade tea leaf G1 exhibited pure, sweet characteristics, serving as an excellent aroma-absorbing carrier. The scenting process significantly imparted jasmine fragrance to the finished product, although its efficacy was constrained by tea leaf grade. GH1 finished tea exhibited a fresh, vibrant, and rich aroma with a sweet, mellow fragrance and high floral integration. In contrast, GH3, due to its inferior base material quality, yielded a weak aroma after scenting with limited quality improvement. The initial quality of the tea base is the fundamental determinant of the upper limit of the finished jasmine tea’s sensory quality, while the scenting process is the core means of shaping its signature floral aroma. The combination of high-quality tea leaves and precise scenting techniques is essential for developing the fresh, vibrant, and rich flavour profile of premium jasmine tea. This study reveals that the flavour formation of jasmine tea originates from the foundational quality of the tea leaves, providing a theoretical basis for monitoring the aroma quality of jasmine tea produced from different grades of tea leaves.

Separations doi: 10.3390/separations13030081

Authors: Costas Tsioptsias Ioannis Maletskos George Tachias Thomas Palikrousis Xanthi Ntampou Eleni P. Kalogianni Petros Samaras

Tertiary amines such as N,N-dimethyl-cyclohexylamine (DMCHA) are recently explored as candidate solvents for the extraction and separation of lipids from algal biomass. DMCHA exhibits the interesting property of polarity switching which is based on the interaction of DMCHA with CO2, termed CO2 switching. Although this approach exhibits certain advantages, various issues have to be improved to address for example the duration required for process optimization, the energy demand, or the low solvent recovery. The aim of this work is the examination of amine recovery from an oil extract, utilizing strong electrolytes (SE) such as HCl for protonation and NaOH for deprotonation of amine, instead of conventional CO2 switching. It was found that the acid based hydrophobic-to-hydrophilic switching and the alkali based hydrophilic-to-hydrophobic back-switching carried out in the order of few minutes, a considerably shorter time compared to few hours required by gas switching, resulting in addition to higher amine recovery. In addition, the combined CO2 switching with SE-back switching using NaOH proved to be a promising approach for large-scale applications, exhibiting several advantages related to technical, economic, environmental and safety issues.

Separations doi: 10.3390/separations13030080

Authors: Shijie Zhou Qiang Zhao Zhangke Kang Jizong Wu Zhenguo Song Tao Song Baoyu Cui Haoyu Du

Ultrafine hematite particles (<10 μm), commonly generated in beneficiation circuits, exhibit poor flocculation and slow settling, posing challenges for solid–liquid separation. This study investigates the influence of the anionic polyacrylamide (APAM) molecular weight on ultrafine hematite flocculation under controlled laboratory conditions, combining macroscopic experiments with molecular dynamics simulations (MDSs). Sedimentation tests show that the APAM molecular weight strongly affects settling kinetics, supernatant clarity, and floc structure, with the settling rate, flocculation-stage reaction time, supernatant turbidity, and underflow concentration exhibiting a non-monotonic trend and optimal performance at seven million. Under this condition, particles aggregate most efficiently, achieving a turbidity of 182 NTU, an underflow concentration of 51.5%, and the largest compact flocs, averaging 379.8 μm with a fractal dimension of 1.71. Higher molecular weights (≥9 million) induce chain coiling, reduce floc compactness, increase water retention, and impair settling. MDS indicates that polymer–surface interactions improve with an increasing polymerisation degree only up to an intermediate chain length; a polymerisation degree of 30 exhibits the most favourable extended–flexible conformation, maximal surface enrichment, strongest coordination between carboxyl groups and surface Fe atoms, lowest adsorption energy, and fastest adsorption kinetics. The functional-group distribution and hydrogen-bond analyses show that –NH2 and –COO– groups dominate interfacial interactions, with a polymerisation degree of 30 yielding the highest density of interfacial hydrogen bonds. By correlating macroscopic experiments with molecular-scale observations, this work provides mechanistic insight into how the APAM chain length governs ultrafine hematite flocculation, highlighting the role of polymer conformation and multipoint adsorption in controlling the settling performance.

Separations doi: 10.3390/separations13030079

Authors: Maria Chiliou Vasiliki Louli Kostis Magoulas

Cistus creticus is a species of the Cistus family that exhibits a wide range of bioactivities; therefore, its oil recovery using a green extraction method is of significant importance for both academic research and industrial applications. Thus, the objective of this work is cistus oil recovery by supercritical fluid extraction (SFE) with CO2. To this end, the effect of various process parameters, namely extraction pressure (110–250 bar), extraction temperature (40–60 °C), and solvent flow rate (1–3 kg/h), on the yield of the process was examined. It was shown that an increase in temperature, and particularly in pressure, positively affects the yield, while the flow rate increase mainly enhances the extraction rate. Hence, the highest yield (8.58% wt) was obtained at 60 °C, 250 bar, and 3 kg/h after 150 min of extraction. Furthermore, the experimental data regarding the kinetics of SFE were correlated successfully by a mass balance model based on Lack’s plug flow model. In addition, the comparison of SFE extracts obtained under intermediate conditions with the essential oil produced by hydrodistillation revealed the extraction of heavier compounds, notably a high content of linoleic acid. Finally, the addition of a small amount of co-solvent (5% wt ethanol) to the SFE process enhanced yield (9.53% wt) as well as antioxidant activity (IC50 = 95.4 mgextract/mL) and total phenolic content of the extract (23.2 mgGAE/gextract). Thus, SFE could become a promising alternative to conventional extraction with ethanol, which exhibited the highest yield (28.5% wt) and a high antioxidant activity (IC50 = 3.2 mgextract/mL), given SFE’s shorter extraction duration.

Separations doi: 10.3390/separations13030078

Authors: Danija Lazdiņa Inga Mišina Krists Dukurs Paweł Górnaś

Current industrial sources of tocotrienols are almost entirely composed of tropical monocots. However, recent reports have observed significant tocotrienol (T3) contents in eudicot families, including Passifloraceae. While passion fruits are also tropical, their cultivation is not strictly limited to rainforests, and seeds are often a by-product of fruit processing. To elucidate tocochromanol production in the Passifloraceae family, seeds (54 samples representing 18 species) were gathered from botanical gardens worldwide. Ultrasound-assisted extraction in ethanol (UAEE) was compared with the standard saponification protocol as a greener alternative. Tocotrienols constituted a major percentage (48–91%) of Passifloraceae species’ seed tocochromanols, and γ-T3 (12–53%) and δ-T3 (8–68%) were major contributors. Although a higher δ-T3 content was observed in some Passiflora species, it was less consistent than the γ-T3 content between and within species. The highest total tocochromanol content was observed in P. subpeltata (28.98 ± 5.83 mg 100 g−1 dry weight). The UAEE protocol recovered tocotrienols and tocopherols at degrees similar to those of saponification (100% and 93%, respectively). Therefore, UAEE could also be proposed for the effective recovery of these valuable phytochemicals from by-products of Passiflora fruits.

Separations doi: 10.3390/separations13030077

Authors: Yao Li Huilin An Zezuo Jiang Haixiang Tan Chunlin He

Addressing the need for efficient separation of critical elements from NdFeB magnets, this study introduces, for the first time, a D001 cation exchange resin for the selective separation Co(II) from Nd(III) and Dy(III). At pH 5, the resin adsorbs Nd and Dy with high capacities (97.57 and 86.38 mg/g, respectively) and efficiencies (over 98%), but shows low affinity for Co (26.6% efficiency). The resin exhibits excellent stability across a wide pH range of 2–7 and maintains high adsorption performance over five consecutive cycles. The process follows pseudo-second-order kinetics and the Langmuir model. Co(II) is effectively desorbed with high purity (>99%) using 2.5 M H2SO4. Characterization confirms that adsorption occurs via ion exchange on –SO3Na groups. This method successfully separates Co, providing a high-purity stream for further rare earth purification and demonstrating strong industrial potential.

Separations doi: 10.3390/separations13030076

Authors: Hang Yin Yanlong Chen Yingchun Wang Zhihong Shi Xueyan Hu Hongyi Zhang

This study used the QuEChERS method in combination with liquid chromatography–quadrupole-time-of-flight mass spectrometry (LC-Q-TOF/MS) to develop a method for simultaneous detection of 187 pesticides and 10 mycotoxins in Astragalus. The samples were extracted using an acetonitrile–water solution containing 5% formic acid, and the amount of purification materials was optimized through response surface methodology. The results show that 197 compounds exhibit good linear relationships within their respective linear ranges (R2 > 0.995). The screening detection limits (SDLs) and the limits of quantification (LOQs) ranged from 0.001 to 0.02 mg/kg and 0.002 to 0.02 mg/kg, respectively. At the spiked levels of 1, 2, and 10 times LOQ, compound recoveries ranged from 61.5% to 118.9%, 67.1% to 119.6%, and 72.0% to 119.3%, respectively, with relative standard deviations (RSDs) all less than 20.0%. The intra-day precision and inter-day precision are less than 10% and 20%, respectively. This method was applied to detect 20 batches of commercially available Astragalus samples. Six compounds (three pesticides and three mycotoxins) were detected; the residues of aflatoxin and ochratoxin A in two batches exceeded the maximum residue limits and required attention. The established method is simple, rapid, and highly sensitive. It is also reproducible and meets the requirements for the accurate quantitative analysis of multiple pesticide residues and mycotoxins in Astragalus.

Separations doi: 10.3390/separations13020075

Authors: F. Esmeralda Santiago-Martinez Jose A. Rodriguez Eva M. Santos Alicia C. Mondragon-Portocarrero Jorge Lopez-Tellez

Saturated fatty aldehydes are products from lipid oxidation that negatively affect the organoleptic properties and nutritional quality of food and represent a risk to human health. For this reason, they are frequently used as indicators of oxidation in food safety. Usually, their determination is carried out by derivatization using an excess of 2,4-dinitrophenylhydrazine (DNPH), but the excessive use of derivatizing agents requires a high proportion compared to the analyte concentration to ensure a complete reaction, which causes interferences and limits the chromatographic separation of derivatized products. In this context, the encapsulation of DNPH in alginate spheres is proposed to determine aldehydes concentration in edible vegetable oil samples, allowing the gradual release of DNPH to form the corresponding hydrazones, which were subsequently separated and analyzed by HPLC-DAD. The proposed method was optimized by a Taguchi L9(34) experimental design, validated, and applied for the determination of aldehydes in edible oils. Limits of detection in the intervals of 0.77 to 1.41 mg L−1 were obtained with adequate precision (expressed as relative standard deviation < 10%), which are suitable values for monitoring lipid oxidation in foods The proposed methodology represents a viable alternative to apply in quality control studies and lipid degradation profiles.

Separations doi: 10.3390/separations13020074

Authors: Bingjie Li Pu Yang Binjie Wang Wenqian Kang Changzhi Li Li Liu Huashan Gao Suqing Wu Chunzhen Fan

Stormwater and greywater are increasingly recognized as freshwater resources, and the effective separation and reutilization of nitrogen (N) and phosphorus (P) from these streams is vital for water quality improvement and urbanization sustainability. In this study, we constructed a pilot-scale hydroponic green roof wetland system planted with two economically important Chinese herbal plant species (Mentha spicata L. (ML) and Basella alba L. (BL)) to separate and reutilize N and P from synthetic stormwater/greywater. The results reveal that the highest plant biomass was obtained at an ML:BL ratio of 1:3, indicating their superior adaptation to rooftop hydroponics with synthetic stormwater/greywater. This configuration also achieved the strongest water purification, with substantial separation and reutilization efficiency of N (82.09%) and P (81.90%). Furthermore, the lowest microbial richness in the ML roots at this specific plant ratio suggested that increasing BL may enhance ML’s allelopathic effects. An increase in the BL proportion was further associated with a gradual shift in the dominant ML root-associated microorganisms toward microeukaryotic taxa. The green vegetation of the two plant species also effectively suppressed algal blooms (especially diatoms) in the hydroponic rooftop system. This study demonstrates that a Chinese herb-based green roof wetland system can effectively separate and reuse N and P from stormwater/greywater while concurrently purifying water and producing economic crops.

Separations doi: 10.3390/separations13020073

Authors: Wanzhong Liu Guichuan Ye Penghui Liu

Spiral separators commonly face the issue of particle misplacement during fine particle separation, which severely limits separation accuracy. This study employs a coupled CFD-DEM numerical simulation method to systematically investigate the influence mechanism of transverse inclination angle (10°, 15°, 20°) on particle moving behavior. The results show that the separation process exhibits distinct stage characteristics, which can be divided into an initial stage (first 1/3 turn), a transition stage (1/3 to 2 turns), and a quasi-steady stage (after 2 turns). A steeper angle (20°) optimizes the flow field, reducing the inner low-velocity zone and widening the high-velocity core, which promotes inward migration of particles. This enhances the enrichment of high-density particles while effectively suppressing their mixing into the clean coal product at the outer edge. For difficult-to-separate fine particles below 0.1 mm, although complete separation is challenging, increasing the transverse inclination angle still shows a clear reduction in the misplacement of high-density particles, providing a controllable approach for improving the quality of the outer edge product. This study offers theoretical insights and design guidance for optimizing spiral separator structures and enhancing fine coal separation efficiency.

Separations doi: 10.3390/separations13020072

Authors: Mengshuai Liu Xiaoman Li Mengmeng Zhao Xuyang Jiu Chuang Yao Minglei Tian

Background: Food waste contains abundant (+)-catechin, but its efficient recovery remains challenging. This study aimed to prepare ionic liquid (IL)-modified sorbents and establish an efficient method for (+)-catechin recovery from chocolate waste via solid-phase extraction (SPE). Methods: Three series of IL-modified sorbents (Sil-IL, ZIF67-IL, Sil@ZIF67-IL) were synthesized. Their adsorption performance was evaluated under different conditions; adsorption isotherm and kinetic data were fitted to Langmuir/Freundlich and pseudo-first/second-order models, respectively. Sorbent stability and (+)-catechin recovery from chocolate waste extracts were tested. Results: Sil@ZIF67-Hmim showed the highest adsorption capacity (154.4 mg/g) at 25 °C within 120 min. Adsorption followed the Langmuir model (R2 = 0.99), indicating chemisorption. Sil@ZIF67-Hmim was subjected to repeated solid-phase extraction (SPE) for five consecutive days; the recovery rate ranged from 98.1% to 99.2%, and the relative standard deviation (RSD) was 3.2–4.4%. Conclusions: Sil@ZIF67-Hmim is a high-efficiency sorbent for (+)-catechin recovery from chocolate waste, providing a novel approach for food waste valorization and highlighting the application potential of IL-modified MOF-silica composites.

Separations doi: 10.3390/separations13020071

Authors: Lenian Qu Yuxin Fang Ziyi Wan Meiling Feng Xiaoying Huang

As a fission product of 235U or 239Pu, 90Sr is a β-emitting radionuclide with a relatively long half-life (t1/2 = 28.9 years). Due to its high solubility, easy environmental mobility, and propensity for bioaccumulation within the food chain, the development of efficient materials for the selective capture of 90Sr2+ is critical for the safe disposal of nuclear waste and environmental protection. In this study, a layered metal sulfide, K1.36Cd1.12Bi2.80S6 (denoted as KCBS), was synthesized via the high-temperature solid-phase method using K2CO3 as the potassium source. KCBS demonstrates high adsorption performance towards Sr2+, achieving a maximum adsorption capacity (qmSr = 77 mg·g−1). Moreover, it can maintain high adsorption efficiency (RSr > 84.15%) across a broad pH range of 2.98–12.01. In addition, KCBS exhibits the outstanding selectivity for Sr2+ removal in the presence of excessive Na+ ions and even in actual water samples. KCBS also possesses regenerability, maintaining its superior adsorption capacity for Sr2+ ions over three cycles. The mechanism study by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) analyses indicates that the efficient Sr2+ capture is attributed to the ion exchange between Sr2+ and interlayer K+ ions in KCBS. This research further highlights the potential of layered metal sulfide ion exchange materials for radionuclide remediation.

Separations doi: 10.3390/separations13020070

Authors: Lushuai Yao Zishuai Liu Zhihui Zhao Qianwen Li Enhao Li Huiyang Lin

Neodymium–iron–boron (NdFeB) waste represents a valuable secondary source of rare earth elements (REEs). However, existing recovery technologies face several challenges, such as the difficulty of selectively recovering REEs, the generation of large volumes of secondary iron-rich slag, and an overall low level of comprehensive resource utilization. In this study, Aliquat 336 was applied for the selective extraction and separation of REEs and iron (Fe) from hydrochloric acid leachate derived from NdFeB waste. Experimental results showed that under optimized conditions—specifically, a 15% Aliquat 336 concentration, an organic-to-aqueous phase ratio of 1:2, and a 2 min extraction time—Fe extraction efficiency reached 99.93% after three-stage countercurrent extraction, while REEs were predominantly retained in the aqueous phase. Subsequent oxalic acid precipitation of the raffinate yielded RE2(C2O4)3·10H2O with a purity of 99.60%. Moreover, under stripping conditions of 2 mol/L NaOH, a phase ratio of 2:1 (aqueous to organic), and a 2 min contact time, over 99.21% of Fe was stripped after three-stage countercurrent stripping, resulting in Fe(OH)3 with a purity of 99.26%. The extraction mechanism followed an anion-exchange process: under high chloride ion concentrations, Fe3+ formed anionic FeCl4− complexes, which were exchanged with Cl− ions in Aliquat 336 and transferred into the organic phase, whereas RE3+ cations remained in the aqueous phase, enabling efficient separation of Fe and REEs. These findings provide important insights for improving the comprehensive utilization of NdFeB waste and promoting the green and sustainable development of secondary rare earth resource recycling.

Separations doi: 10.3390/separations13020069

Authors: Huanlian Wang Fang Wang Lu Di Chuanyun Gao Deli Zhang Shaoqing Wang Min Lv Weiming Yi

This study investigates the preparation of a composite material by immobilizing Bacillus subtilis on biochar derived from chicken manure biogas residue for the removal of Cr(VI) from wastewater. The results demonstrated that the composite material (Bacillus subtilis immobilized biochar, BIB) achieved a maximum Cr(VI) removal efficiency of 94.1% in a 100 mg/L Cr(VI) solution within 4 h. The chicken manure-derived biochar not only served as an effective carrier for Bacillus subtilis but also enhanced the Cr(VI) removal efficiency through a synergistic effect with the microorganism. Functional groups such as phosphorus, carboxyl, and hydroxyl groups on the biochar surface played a key role in the sorption of Cr(VI). Bacillus subtilis primarily reduced Cr(VI) to Cr(III) by secreting cellular reductases. The combined action of biochar and Bacillus subtilis increased the Cr(VI) removal rate by 13.71% compared to biochar alone. This study presents a promising approach for Cr(VI) remediation in contaminated water and lays a theoretical foundation for the development of composite materials for Cr(VI) reduction.

Separations doi: 10.3390/separations13020068

Authors: Zhe Xia Xinyu Gao Thor Halldorson Nipuni Vitharana Chris Marvin Philippe J. Thomas Gregg T. Tomy

This study details the validation of a novel microbead beating extraction (MBE) technique for the analysis of polycyclic aromatic compounds (PACs) in sediments. The method’s performance was evaluated against international analytical validation criteria, including trueness, precision, measurement uncertainty and robustness. Limits of detection and quantitation were consistently low (≤6.5 and 21 ng g−1, respectively), trueness for the majority of analytes fell within accepted performance criteria, and repeatability values for most analytes were generally <10%. Analytical data confirm the method’s reliability, with more than 80% of certified analytes in two certified reference materials (CRMs) meeting the satisfactory z-score (∣z∣ ≤ 2.0). Furthermore, the method’s inter-laboratory repeatability, as measured by HorRat values, fell within the range recommended by the Association for Official Analytical Chemist for most analytes, and combined measurement uncertainties showed no statistical difference from the certified uncertainties of the CRMs. Incorporating an in situ cleanup step enabled the MBE method to substantially reduce extraction times (<15 min) and reduces solvent consumption by ~60% compared with conventional pressurize fluid extraction while maintaining good quality data objectives. By meeting or exceeding well-established metrics for good laboratory performance, the MBE method demonstrates reliability, efficiency, and a greener approach for the routine analysis of PACs in sediments.

Separations doi: 10.3390/separations13020067

Authors: Linhe Sun Ying Yang Jianguo Yu

l-menthol is one of the most popular flavors in the world. The separation of menthol enantiomers is crucial because of the unpleasant taste of d-menthol. This work presents the chiral separation of racemic menthol by simulated moving bed chromatography for the first time. Six preparative columns packed with amylose 3,5-dimethylphenylcarbamate coated on silica gel were used for separation, and a mixture of n-hexane/isopropanol was selected as the mobile phase. The hydrodynamic properties of the SMB columns were studied to minimize the packing asymmetry in the SMB experiment. The binary adsorption isotherm of menthol enantiomers was measured by the adsorption–desorption method. Fixed-bed batch chromatography was carried out to evaluate the adsorption kinetic behavior. Mathematical models, considering the mass transfer resistance and axial dispersion, were applied to describe the dynamics of the chromatographic separation process. The SMB process for chiral separation of racemic menthol was designed by evaluating the separation region using simulations. Reasonable agreements were achieved between the predicted results and the experimental results. Purities for both the extract and raffinate were above 99.0%, and a productivity of 0.267 gracemate/(LCSP∙min) and a solvent consumption of 0.431 L/gracemate were achieved.

Separations doi: 10.3390/separations13020066

Authors: Muling Sheng Zishuai Liu Zhihui Zhao Qianwen Li Wenbin Liu Heng Luo Yancheng Lv

Conventional hydrometallurgical processes typically employ inorganic acids as leaching agents; however, these processes are frequently associated with significant environmental pollution and suffer from poor metal selectivity. Oxalic acid, as a green alternative leaching agent, demonstrates considerable application potential owing to its mild acidity, strong reducing capability, and superior complexing properties. This paper presents a systematic review of recent advances in the application of oxalic acid in hydrometallurgy, encompassing the coordination chemistry between oxalic acid and metal ions, its role as a selective leaching agent, and strategies for handling multicomponent oxalate-rich solutions. Furthermore, the industrial prospects of oxalic acid-based leaching technologies are discussed. Research indicates that oxalic acid exhibits high selectivity and efficient leaching performance for critical metals—including vanadium, lithium, cobalt, nickel, and gallium—from both primary ores and solid secondary resources. The underlying leaching mechanism primarily involves the formation of stable chelation complexes between oxalate anions and high charge-density metal ions, or valence state modulation via reduction, enabling selective dissolution and separation of target metals. In multicomponent oxalate systems, where metals predominantly exist as anionic complexes, established enrichment and purification approaches include anion exchange extraction, as well as precipitation techniques based on valence adjustment and double salt crystallization. To advance the industrial implementation of oxalic acid leaching technologies, further in-depth investigation is required into the recycling mechanisms of oxalic acid and the fundamental reaction pathways governing leaching and metal recovery processes.

Separations doi: 10.3390/separations13020065

Authors: Jason Devers Philip J. Marriott

The recently introduced solid-state modulator (SSM) is a compact and relatively simple all-in-one solution to thermal modulation for use in comprehensive two-dimensional gas chromatography (GC×GC). In this work, we assess the performance of this modulator through a detailed assessment of its temperature stability and temperature programming capabilities, and corresponding retention time reproducibility. Through replicate analysis, 2D retention time standard deviation was determined to be 0.014 s (ranging from 0.000–0.023 s), corresponding to less than a single acquisition datapoint. Additionally, 1D retention time repeatability in GC×GC was assessed using a ‘super-resolution method’ designed to predict 1D retention based on the modulated peak distribution, and was determined to be comparable to that of conventional GC-MS analysis. A benchmarking framework was developed, which can be applied to future performance evaluations of thermal and other modulators, allowing for a more systematic comparison of modulation strategies.

Separations doi: 10.3390/separations13020064

Authors: Lakshmi Reddi Rex Johnson Kerry K. Gilbert Paola A. Prada-Tiedemann

Blood is a key biological specimen in forensic analysis for both living and deceased individuals, playing a crucial role in drug testing, blood typing, DNA analysis, and bloodstain pattern examination. In forensics, the decomposition of blood holds particular importance because it is a major biological fluid in the human body and undergoes early chemical changes that attract insects and microorganisms to cadaveric sources. The odor signatures produced during the putrefactive process have recently gained forensic relevance, prompting studies to investigate volatile organic compounds (VOCs) from blood, tissues, animal proxies, and human cadavers to enhance human remains detection and recovery via technological or biological means. This study focuses on cadaveric blood odor profiling, evaluating VOC signatures from human cadavers in an anatomy laboratory using solid-phase micro-extraction (SPME) and gas chromatography–mass spectrometry (GC/MS) upon body receipt. A second phase entailed a degradation analysis using 7 human cadavers and a total of 28 postmortem samples repeatedly sampled over a 4-week period. The findings revealed an increasingly complex odor profile as decomposition progresses, with a notable rise in both the variety and concentration of VOCs. Room temperature samples exhibited a more diverse and rapid VOC release, while refrigerated samples showed slower degradation. These insights contribute to a deeper understanding of decomposition patterns and ultimately refine human remains detection methodologies.

Separations doi: 10.3390/separations13020063

Authors: Jingjing Quan Yuting Zheng Lan Yao Lianqing Li Xingming Ning

The highly efficient performance of photoelectrochemical (PEC) water splitting is largely governed by the construction of active interfaces, especially for the star semiconductor/electrocatalyst system. However, traditional strategies struggle to optimize this critical process. To overcome this challenge, we report a fluorine (F) engineering strategy that enables the synchronous modulation of charge transfer and surface catalytic reaction dynamics in a BiVO4/FeCoOOH-integrated photoanode. Various characterization methods confirm that F engineering can activate the BiVO4/FeCoOOH/electrolyte interfaces. Benefiting from these positive effects, the optimized BiVO4/FeCoOOH-F photoanode achieves a relatively high photocurrent density of 5.46 mA/cm2 at 1.23 V vs. RHE, along with outstanding photostability and a small Tafel slope of 96.5 mV dec−1. This study provides new insights into F-based interface manipulation, offering a promising route to developing high-performance semiconductor/electrocatalyst systems for efficient and stable PEC water splitting applications.

Separations doi: 10.3390/separations13020062

Authors: Luogeng Ge Fengsheng Guo Jiawei Wang Jing Zhang Qi Lu Yuanyi Wang Xingdong Lv Ziling Peng Xian Zhou Xia Chen Wei Han Zeyu Fan

Rapid growth of water conservancy/hydropower projects has spurred rising demand for sand-gravel aggregates. Under strict water use and zero-waste policies, treating wet-process aggregate washing wastewater is challenging. Flocculants—key chemicals in this process—directly influence treatment efficiency and operational costs via their type, dosage, and efficacy. Further development of the intelligent control system for flocculant dosing can reduce flocculant consumption by 50% to 67%. However, existing studies have an insufficient understanding of the identification of emerging contaminants in aggregate washing wastewater and the migration of flocculants in multi-medium environments, as well as a lack of research on the synergistic effects of multiple flocculants. Another key core challenge lies in the accurate identification of the impact of flocculant residues on concrete performance, along with the problems of high cost and poor adaptability of intelligent systems. Future research directions will focus on precise flocculation, residue control and resource utilization to drive the development of efficient and environmentally friendly treatment technologies.

Separations doi: 10.3390/separations13020061

Authors: Bakheit Mustafa Ard Elshifa M. E. Mohammed

In this study, cerium oxide (CeO2) nanoparticles were successfully synthesized using a simple and cost-effective hydroxide-mediated precipitation method. Comprehensive characterization (XRD, SEM, TEM, FTIR, BET, and UV–Vis) confirmed the formation of uniformly distributed nanoparticles with an average size of ~100 nm, a well-defined crystalline structure, and a high specific surface area of 118.96 m2/g. The CeO2 nanoparticles also exhibited a mesoporous framework with a pore volume of 0.39 cm3/g and an average pore radius of 2.27 nm, demonstrating favorable properties for adsorption applications. Adsorption experiments showed that CeO2 nanoparticles effectively removed Pb2+ from aqueous solutions, achieving a maximum experimental adsorption capacity of 192 mg/g and a removal efficiency of 80% at pH 6 under the tested conditions. Kinetic analysis revealed that the pseudo-second-order model best described the adsorption process, suggesting chemisorption as the dominant mechanism, while equilibrium data were more accurately represented by the Langmuir isotherm model, which predicted a theoretical monolayer capacity (Qm) of 714.2 mg/g. Overall, the findings demonstrate that CeO2 nanoparticles possess a strong affinity toward Pb2+ ions and exhibit promising adsorption performance, indicating their potential applicability for the treatment of lead-contaminated wastewater and their suitability for reuse following regeneration.

Separations doi: 10.3390/separations13020060

Authors: Haibao Zhao Peiyuan Li Hanxiao Liu Tao Liu Zhengda Yang

Corona quenching is a major obstacle to the stable and efficient operation of electrostatic precipitators (ESPs) in coal-fired power plants, particularly under high-ash coal combustion. This study evaluates a novel double-V labyrinth pre-collection device as an active strategy to mitigate corona quenching. Field measurements from a 660 MW ultra-supercritical coal-fired unit, combined with computational fluid dynamics (CFD) simulations, demonstrate that the retrofit significantly improved inlet flow uniformity and reduced fly ash concentration before the ESP. Consequently, corona discharge stability was enhanced, overall collection efficiency increased from 99.42% to 99.92%, and outlet fly ash concentration decreased from 81 mg/m3 to 20.5 mg/m3. Although the pressure drop rose modestly (128 Pa to 187.5 Pa), the overall ESP energy demand was reduced due to more stable operation at lower voltages. These results confirm the technical feasibility and engineering applicability of pre-collection technology, providing a cost-effective solution to overcome corona quenching and ensure ultra-low emission compliance in large coal-fired units.

Separations doi: 10.3390/separations13020059

Authors: Zhengnan Jiang Guanyu Zhou Wenchao Bu Zhenhai Huang Chunlin He

Water with a high fluoride content poses a serious threat to both public health and the natural environment. To enhance fluoride ion removal efficiency, a modified activated carbon adsorbent (HPAC-La) was synthesized by impregnating soybean protein in a lanthanum nitrate solution, followed by freezing–drying and carbonization. The results confirmed that lanthanum nitrate modification significantly improved the adsorption performance. Under optimised experimental conditions (pH = 2.0, [F−] = 300 mg·L−1, 12 h, 298 K), HPAC-La exhibited a maximum adsorption capacity for fluoride ions of 126.7 mg·L−1, significantly higher than that of unmodified HPAC (86.1 mg·L−1). The adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating monolayer chemisorption. The mechanism involves ion exchange via surface hydroxyl groups and fluoride coordination with La sites. This study proposes a method for developing highly efficient adsorbents for the treatment of fluoride-contaminated wastewater.

Separations doi: 10.3390/separations13020058

Authors: Dimitris Valatsos Kostas Gkountanas Yannis Dotsikas

Paracetamol (PAR) and orphenadrine citrate (ORPH) are two active substances commonly used in combination medicinal products, due to the analgesic effect of paracetamol and the muscle relaxant effect of orphenadrine, with a therapeutic indication of mild to moderate acute musculoskeletal pain. The aim of this work is to develop and validate an isocratic HPLC method for the simultaneous determination of PAR and ORPH in tablet formulation. Preliminary experiments showed that an analytical column with a chemically bound phenyl phase was required. A Box–Behnken design (BBD) was utilized to optimize the analytical method for two key responses, PAR asymmetry factor (AsymPAR) and ORPH capacity factor (kORPH), with three numerical factors: percentage of ACN in mobile phase (A); pH (B); and salt concentration in the aqueous solution (C). The optimized method consists of a Pinnacle DB Biphenyl (250 × 4.6 mm) 5 µm column, and a mobile phase of 37%/63% v/v ACN-NaH2PO4·H2O in 29 mM aqueous solution, pH = 2.5. The flow rate was set to 1.5 mL/min and detection occurred at 215 nm. After the optimization process the following chromatographic conditions were selected and the method was validated for various ICH parameters covering system suitability, specificity, linearity (R2 = 1.00), precision (%RSD ≤ 2), accuracy (98% ≤ %Recovery ≤ 102%), and robustness. Finally, the environmental friendliness of the novel method was assessed by using the Analytical GREEnness (AGREE) metric tool, obtaining a score of 0.67.

Separations doi: 10.3390/separations13020057

Authors: Qin Wang Yaohui Xu Jinqiang Yu Runhong Xia Zhiyun Jiang Yuan Zhang Fangyu Xiong

To develop low-cost and renewable materials for treating dye wastewater, an efficient biosorbent was prepared from Bambusa emeiensis bamboo powders (BPs) via a simple alkali pretreatment. Systematic investigation revealed that NaOH concentration was critical for enhancing adsorption performance. Under optimal conditions (NaOH ≥ 0.2 mol/L, dosage = 10.0 g/L), the BPs achieved over 96% removal of cationic Methylene Blue (MB, 20 mg/L) within 20 min, demonstrating rapid kinetics. The adsorption process followed the Langmuir isotherm model with a maximum adsorption capacity of 4.1 mg/g without adjusting the pH of the solution and complied with the pseudo-second-order kinetic model. Thermodynamic analysis confirmed the spontaneous (ΔG < 0) and exothermic (ΔH = −52.73 kJ/mol) nature of the adsorption. Notably, the alkali-treated BPs exhibited a pronounced preference for the cationic dye, achieving a high removal rate of 96.5% for MB, in contrast to a much lower removal of 23.6% for the anionic dye AO7 under identical single-dye conditions, attributed to the enhanced surface negative charge after alkali treatment. Furthermore, the BPs maintained a high removal efficiency of 91.2% after eight adsorption-desorption cycles using 0.1 mol/L HCl as eluent, demonstrating excellent reusability. This study presents a feasible and sustainable strategy for designing regenerative bamboo-based biosorbents with rapid and preferential adsorption capabilities for cationic dye wastewater.

Separations doi: 10.3390/separations13020056

Authors: Nenad Radić Aleksandra Nastasović Tamara Tadić Zorica Vuković Jugoslav Krstić Bojana Marković

In this study, magnetic porous glycidyl methacrylate and ethylene glycol dimethacrylate copolymer (mP) grafted with tetraethylenepentamine (mP-TEPA) obtained in a two-step procedure was tested as the CO2 sorbent. The morphological, textural, structural, and thermal characterization of the sample was determined by scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDS), mercury intrusion porosimetry (MIP), nitrogen physisorption at 77 K, Fourier transform infrared spectroscopy in ATR mode (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), elemental analysis, and thermogravimetric analysis (TGA). The effects of thermodynamic and kinetic parameters, as well as the adsorption/desorption mechanism on the CO2 sorption ability of mP-TEPA, were investigated using a pulse gas chromatographic method. Under optimal adsorption conditions, the CO2 sorption capacity reached 6.20 mmol CO2/g (6.20 × 10−2 mmol CO2/m2). Temperature-programmed desorption (TPD) experiments were conducted to calculate the activation energy of CO2 desorption. The low desorption activation energy of 18.80 kJ/mol and high desorption rate, with stable CO2 uptake after ten adsorption/desorption cycles, suggest that mP-TEPA is a potentially excellent sorbent for CO2 adsorption.

Separations doi: 10.3390/separations13020055

Authors: Xiaofei Meng Xiaoping Zou Yingping Jiang Haitao Zhou Jiantao Zhao Shengmei Zhang Junqi Zhang

With the rapid expansion of the global lithium battery industry, the demand for lithium as a critical raw material continues to grow. Lithium precipitation mother liquor still contains considerable concentrations of lithium ions (Li+), but they generally exhibit a high sodium-to-lithium ratio, which makes the separation of lithium from sodium particularly challenging. Solvent extraction is recognized as a viable approach for challenging Li+/Na+ separation due to its high selectivity, operational flexibility, and scalability. A comprehensive assessment and comparison of various extraction systems are therefore essential to facilitate the sustainable recovery of lithium from precipitation mother liquor. This review summarizes the commonly used extraction systems, including organophosphorus extractants, ketone-based extractants, macrocyclic compounds, ionic liquids, and deep eutectic solvents. A systematic analysis is provided regarding their extraction mechanisms, applicable conditions, and respective advantages and disadvantages. Finally, perspectives and suggestions are offered on future research directions and improvement strategies for different extraction systems, along with an outlook on the potential of combined enhancement technologies.

Separations doi: 10.3390/separations13020054

Authors: Elli Katsouli Konstantia Graikou Evgenia Panou Nikolas Fokialakis Ioanna Chinou

Primula vulgaris Huds., one of the 33 Primula L. species native to Europe, occurs across diverse habitats, including the biodiversity hotspot of the Prespa Lake region (NW Greece). Building on previous phytochemical studies, the present work provides the first detailed characterization of flavonoids from the aerial parts of the species growing wild in the area. Using classical chromatographic separation methods combined with spectrometric techniques, seven metabolites were isolated and structurally elucidated from the dichloromethane and methanol extracts. These included flavone (1), 2′-methoxyflavone (2), 3′-methoxyflavone (3), 3′-hydroxy-4′,5′-dimethoxyflavone (4), kaempferol-3-O-β-glucopyranosyl-(1→2)-β-glucopyranosyl-(1→6)-β-glucopyranoside (6), 3′-hydroxyflavone-4′-O-β-glucopyranoside (7) and 5,6,2′,3′,6′-pentamethoxyflavone (5), which was reported for the first time in this species. Additionally, the total phenolic content (TPC) of the methanol extract was determined using the Folin–Ciocalteu method, demonstrating 46.46 ± 2.48 mg GAE/g extract, while through the DPPH radical scavenging assay, it expressed moderate activity. Overall, these results provide novel insights into the flavonoid composition of Greek P. vulgaris and support its potential for further pharmacological investigations and herbal applications.

Separations doi: 10.3390/separations13020053

Authors: Anna Karoline Freires de Sousa Anna Katharina Medeiros de Brito Hugo Guimarães Matos José Lázaro da Silva Fernandes Francisco Lucas de Lima Carneiro Francimarcio Geraldo da Silva Gambarra Wagner Brandão Ramos Tellys Lins Almeida Barbosa Meiry Gláucia Freire Rodrigues

The continuous release of pharmaceutical compounds into aquatic environments poses significant challenges to environmental sustainability, as conventional wastewater treatment plants are often ineffective in removing recalcitrant and bioactive molecules. In this study, the adsorption performance of nanoclay was systematically evaluated for the removal of nystatin, a polyene antifungal of emerging environmental concern, from aqueous solutions. The effects of solution pH, adsorption kinetics, equilibrium isotherms, and adsorption mechanisms were investigated under environmentally relevant conditions. Nanoclay exhibited outstanding removal efficiency, exceeding 98% across a wide pH range (3–11), thereby demonstrating strong operational robustness and minimal sensitivity to pH variations. Structural and spectroscopic analyses (XRD and FTIR) confirmed that adsorption occurred predominantly on the external surface of the nanoclay, without significant disruption of its lamellar structure, and was governed mainly by hydrophobic interactions and hydrogen bonding. Kinetic data were best described by the pseudo-second-order model, with rapid equilibrium achieved within approximately 20 min, indicating high affinity between nystatin and the adsorbent surface. Equilibrium data were best fitted by the Sips isotherm model, reflecting surface heterogeneity and a favorable adsorption process, with a high maximum adsorption capacity of approximately 911 mg/g. A preliminary cost analysis revealed low raw material costs, while energy consumption, particularly during drying, was identified as the main economic limitation. Overall, the results highlight Nanoclay as an efficient, robust, and promising adsorbent for the sustainable removal of hydrophobic pharmaceutical contaminants from water and wastewater.

Separations doi: 10.3390/separations13020052

Authors: Jie Shang Hui Zhao Dun Wang

The genus Isaria is a group of abundant and widely distributed entomopathogenic fungi that plays an important role in the history of traditional Chinese medicine. Entomopathogenic fungi with medicinal value were collected from the field, and optimal temperature and growth media compositions were investigated to establish a theoretical foundation for the future development of these strains. A strain of Isaria cateniobliqua, designated ICF, was isolated from soil in the Hualongshan National Nature Reserve in southern Shaanxi. The optimal cultivation temperature and nutrient solution were screened, and the effects of subcultivation on mycelium production, metabolite production, and hydroxyl radical scavenging activity of strain ICF were investigated. The optimal growth temperature for strain ICF was determined to be 21 °C, with the ideal culture medium consisting of glucose and tussah silkworm pupa powder supplemented with KH2PO4 and MgSO4. Mycelium production and cordycepin content peaked in the fourth generation (G4), whereas peak metabolite production and cordycepic acid production occurred in the fifth generation (G5). Polysaccharide content was highest in the first generation (G1), and hydroxyl radical scavenging activity was optimal in G4. Exploring the optimal culture conditions of the strain provides a theoretical basis for its development, utilization, and industrial production for medicinal applications.

Separations doi: 10.3390/separations13020051

Authors: José Luís Guedes Luís Durão Luana M. Rosendo Tiago Rosado Eugenia Gallardo

Herbicides are widely used agrochemicals and are increasingly recognised as contaminants of emerging concern in aquatic environments due to their extensive application, environmental persistence, and potential ecological and human health impacts. Their determination in water presents significant analytical challenges, as these compounds occur at trace to ultra-trace levels and encompass a wide range of chemical properties, including highly polar and ionic species as well as transformation products. This review provides a critical overview of recent advances in separation technologies for the analysis of herbicides in water, based on peer-reviewed studies published between 2020 and 2025 retrieved from the PubMed and Scopus databases. The discussion focuses on developments in sample preparation, extraction strategies, chromatographic separation, and detection techniques, with particular attention to analytical performance and sustainability. The reviewed studies demonstrate that solid-phase extraction remains central to achieving the lowest detection limits, while miniaturised and greener extraction approaches are increasingly adopted to reduce solvent consumption and simplify workflows. Advances in chromatographic separation and detection, especially liquid chromatography coupled to tandem mass spectrometry, have further enhanced sensitivity and selectivity for a broad range of herbicides. Overall, this review highlights current analytical capabilities and emerging trends, outlining future directions for reliable and sustainable monitoring of herbicides in aquatic environments.

Separations doi: 10.3390/separations13020050

Authors: Ya Wang Peng Zhao Honghong Yi Xiaolong Tang

Obtaining the adsorption equilibrium coefficient (Kd) of organic compounds on microplastics (MPs) is critical for understanding their environmental behaviors. Given the limited availability of these Kd values, it is imperative to develop predictive models for rapid acquisition of Kd values for different MPs. Herein, seven machine learning-based algorithms, i.e., MLR, RF, GBDT, XGBoost, CatBoost, LightGBM and SVM, were used to establish predictive models on the basis of 173 logKd values in freshwater. The evaluation parameters, including R2t, RMSEt, Q2v, RMSEv and Q2, indicate that the developed models have a satisfactory predictive capability. The developed MLR models can predict the logKd values for chlorinated polyethylene (CPE), polybutylene succinate (PBS), polycaprolactone (PCL) and low-density polyethylene (LDPE) MPs. Given the limited performance of MLR in predicting adsorption on PE MPs, RF, GBDT, XGBoost, CatBoost, LightGBM and SVM were employed to develop predictive models, which significantly enhanced the predictive accuracy. The predictive models for PE MPs have a wider AD, covering organic compounds with different functional groups than previous models. Hydrogen bonding, hydrophobic, electrostatic and dispersion interactions may be involved in adsorption. The developed models can serve as efficient tools for estimating the Kd values for different MPs in freshwater, thereby providing the necessary data for evaluating the environmental risks of organic compounds and MPs.

Separations doi: 10.3390/separations13020049

Authors: Yongdong Liu Maria Górecka Jonathan Kennel Merrik Kobarfard Tadeusz Górecki Beth Parker

Rock matrices, as low-permeability media, play a critical role in controlling the persistence and fate of groundwater contaminants. Accurately quantifying contaminant mass stored in these matrices is therefore essential for understanding contamination transport processes. In this study, a microwave-assisted extraction (MAE) method was developed to accelerate the complete extraction of trichloroethylene (TCE) from rock samples. Because microwave–sample interactions depend on multiple factors, extraction conditions, including solvent type, temperature, and extraction time, were optimized using dolostone samples collected from industrial sites with decades-old contamination in Guelph, Canada. Method performance was evaluated through extensive comparison of the newly developed MAE procedure with a conventional shake-flask extraction method used as a reference. In addition, the necessity of field preservation was assessed, given its importance in the overall analytical workflow and accuracy of total mass concentrations and mass stored. The MAE method provided recoveries comparable to or greater than those obtained with the reference method, while avoiding several drawbacks of the shake-flask approach, such as sample cross-contamination during prolonged extraction times over several weeks. Its shorter processing time and faster turnaround support rapid, field-based decision-making. Field preservation was determined to be essential, as non-preserved samples consistently yielded lower measured concentrations than preserved samples.

Separations doi: 10.3390/separations13020048

Authors: Jiancai Sui Yang Liu Zhenhua Wang Tao Li Kun-Yu Gao Jin-Ke Chu Yang-Guang Zhang Hui Shi Jihai Tang Ming Xia

Dimethyl carbonate (DMC) and methanol (MeOH) form a binary minimum-boiling homogeneous azeotrope, and thus conventional distillation cannot achieve complete separation. The extractive distillation (ED) with o-xylene as a heavy entrainer in our recent work possesses significant energy saving and achieves a high purity of 99.9% DMC compared with the pressure-swing distillation (PSD). For a fair comparison, both ED and PSD were evaluated against the same minimum product specifications (DMC ≥ 99.5 wt% and MeOH ≥ 98.0 wt%), noting that the recovered MeOH stream was recycled to the reactive distillation column rather than treated as a final product. However, the dynamic performance of this ED is still unclear, and all the benefits of the ED are reasonable only under good dynamic controllability. In this work, the dynamic controllability of the ED process was compared with that of the PSD one. Both processes were evaluated under a unified temperature-control philosophy, including conventional fixed R. Closed-loop dynamic simulations were performed under ±10% step disturbances in feed flowrate and composition. It was revealed that under the tested disturbances, DMC purity was maintained close to the high-purity target (≈99.9 wt%) in the ED process, whereas larger deviations and a lower attainable DMC purity were obtained in PSD. The results provide a control-oriented basis for the selection and further development of special distillation schemes for MeOH/DMC azeotropic separation.

Separations doi: 10.3390/separations13020047

Authors: Xiangrong Li Xiaoyang Guo Xiaowei An Peifen Wang Xuli Ma Xin Du Xuejin Ren Xuemei Wang

The development of electrode materials that combine high capacity with high anion selectivity is critical for chloride separation from complex aqueous matrices. Here, a NiFe LDH/BiOCl composite film electrode was fabricated on carbon paper via sequential electrodeposition and employed for electrically switched ion exchange (ESIX) of chloride. The composite delivers higher reversible chloride uptake than either NiFe LDH or BiOCl alone under identical electrochemical conditions, together with enhanced selectivity in mixed−anion solutions. Mechanistically, the synergy originates from the combination of (i) the high anion−exchange capacity and redox−tunable layer charge of NiFe LDH and (ii) halide−affinitive BiOCl domains that facilitate voltage−gated uptake/release; the heterointerface further improves charge/ion transport, enabling more effective electrochemical utilization. The electrode maintains stable cycling performance with high regeneration efficiency over repeated ESIX operation. Compared with representative LDH− or BiOX−based ESIX electrodes reported for halide capture, the proposed composite shows competitive chloride selectivity and reversible cycling, supporting its potential for electrochemical separations and water treatment.

Separations doi: 10.3390/separations13020046

Authors: Sasa Savic Sanja Petrovic Zorica Knezevic-Jugovic

Polyphenols are a structurally diverse group of plant secondary metabolites widely recognized for their antioxidant, anti-inflammatory, antimicrobial, and chemoprotective properties, which have stimulated their extensive use in food, pharmaceutical, nutraceutical, and cosmetic products. However, their chemical heterogeneity, wide polarity range, and strong interactions with plant matrices pose major challenges for efficient extraction, separation, and reliable analytical characterization. This review provides a critical overview of contemporary strategies for the extraction, separation, and identification of polyphenols from plant-derived matrices. Conventional extraction methods, including maceration, Soxhlet extraction, and percolation, are discussed alongside modern green technologies such as ultrasound-assisted extraction, microwave-assisted extraction, pressurized liquid extraction, and supercritical fluid extraction. Particular emphasis is placed on environmentally friendly solvents, including ethanol, natural deep eutectic solvents, and ionic liquids, as sustainable alternatives that improve extraction efficiency while reducing environmental impact. The review further highlights chromatographic separation approaches—partition, adsorption, ion-exchange, size-exclusion, and affinity chromatography—and underlines the importance of hyphenated analytical platforms (LC–MS, LC–MS/MS, and LC–NMR) for comprehensive polyphenol profiling. Key analytical challenges, including matrix effects, compound instability, and limited availability of reference standards, are addressed, together with perspectives on industrial implementation, quality control, and standardization.

Separations doi: 10.3390/separations13020044

Authors: Wenmu Feng Shushan Yuan Junyao Dai Jiran Wu Bing Li Yue Wang

Bamboo-derived biochar (BC) is promising for high-salinity wastewater treatment through photothermal evaporation. This study systematically evaluated BCs synthesized at 400–800 °C with residence times of 40 or 70 min. Pyrolysis temperature proved dominant, with 600 °C representing a critical threshold. Below this temperature, BCs maintained high carbon content and polar functional groups but exhibited limited porosity. Above it, structural reorganization enhanced pore development and aromaticity while reducing polar surface groups. Residence time primarily influenced volatile retention, and prolonged pyrolysis led to pore collapse. The optimal BC—produced at 800 °C for 40 min—combined hierarchical porosity with balanced surface chemistry, achieving an evaporation rate of 1.21 kg/m2·h and a photothermal efficiency of 70.45% under high-salinity conditions. Mechanistic analysis indicates that short, high-temperature pyrolysis preserves structural integrity and interfacial activity with minimal energy input. These results establish a thermal processing approach that reconciles carbon stability with surface functionality, offering practical guidance for scaling efficient and sustainable biochar-based wastewater treatment systems.

Separations doi: 10.3390/separations13020045

Authors: Zhihui Zhao Zishuai Liu Hui He Qianwen Li Heng Luo Wenbin Liu Yancheng Lv

Oxalic acid serves as an environmentally benign leaching agent, exhibiting strong reducing and complexing capabilities. In the oxalic acid leachate derived from vanadium-bearing shale, aluminum ions are present as major impurities. Achieving efficient and deep separation of vanadium from aluminum remains a key technical challenge. This study investigates the selective separation of vanadium and aluminum from oxalic acid leaching solutions using solvent extraction with Aliquat 336, supported by density functional theory (DFT) calculations. Experimental results demonstrate that, under optimized conditions, Aliquat 336 enables effective separation of vanadium from aluminum. DFT analysis elucidates the molecular-level interaction mechanism, revealing that the binding affinity of Aliquat 336 for [VO(C2O4)2]2− (ΔG = −287.96 kJ/mol) is significantly stronger than for [Al(C2O4)2]− (ΔG = −186.68 kJ/mol). These results provide a solid thermodynamic basis for the observed selectivity and establish a robust theoretical framework for developing high-efficiency separation processes. This work thus clarifies, for the first time, the mechanistic foundation of vanadium–aluminum separation in oxalic acid systems.

Separations doi: 10.3390/separations13020043

Authors: Yanpeng Chen Ran Mao Rohit Kumar Jianbo Shi Li Yan

Nitrate pollution in groundwater poses severe threats to ecosystems and human health, making the electrochemical nitrate reduction reaction (NO3RR) a promising remediation technology. Conductive metal–organic frameworks (cMOFs) with π-d conjugation, dispersed active sites, and tunable structures are ideal candidates for electrocatalysis. Herein, we synthesized a series of cMOFs (M3(HHTP)2, M = Fe, Zn, Cu, Co, Ni) via conjugated coordination between hexahydroxytriphenylene (HHTP) ligands and metal ions and systematically investigated their NO3RR performance. Electrochemical tests revealed that Fe3(HHTP)2 exhibits superior catalytic performance for nitrate reduction, achieving a high NH3 selectivity of 99.5% and a yield rate of 676.4 mg·gcat−1·h−1 at −1.0 V vs. RHE (reversible hydrogen electrode), along with excellent cyclic and structural stability. In situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy identified key intermediates (*NO2, *NH2OH) and proposed the reaction pathway: NO3− → *NO3 → *NO2 → *NO → *NOH → *NH2OH → *NH2 → *NH3. DFT calculations revealed that Fe center exhibited a lower energy barrier for NO3RR compared to other metal ions (Zn, Cu, Co, Ni). This study demonstrates the significant potential of Fe3(HHTP)2 for efficient NO3RR and provides new insights into the structure-function relationship of cMOF-based electrocatalysts.

Separations doi: 10.3390/separations13020042

Authors: Bin Hao Nannan Zhang Chunli Chen Yuxi Ji Zhihui Zhao Li Wang Hongqiang Dong

An innovative dispersive liquid–liquid microextraction technique utilizing a solid dispersion was established for the quantification of triazine herbicides in environmental water samples. Naturally derived monoterpenoids were utilized as eco-friendly extraction solvents, markedly decreasing the reliance on harmful extraction solvents. A small amount of Pop Rocks candy served as a solid dispersant; the rapid release of carbon dioxide promoted the generation of fine monoterpenoid droplets, effectively replacing conventional hazardous liquid dispersants. The solidification technique of floating organic droplets facilitated the effective phase separation of monoterpenoids from aqueous samples, thereby obviating the need for centrifugation. Triazine herbicides exhibited good linearity within the concentration range of 0.008–0.8 mg/L with correlation coefficients above 0.99 and detection limits of 0.002 mg/L. The proposed method was effectively implemented on surface and groundwater samples, attaining recoveries between 86.4% and 98.0%. Molecular docking analysis suggests a spontaneous binding between the monoterpenoid and triazine herbicides. A comprehensive green assessment utilizing two evaluation tools confirmed the excellent environmental performance of the method. This technique offers superior greenness and simplicity compared with conventional techniques, demonstrating strong potential for application in the environmental analysis of pesticide residues.

Separations doi: 10.3390/separations13020041

Authors: Hequan Zhu Mustapha Muhammad Nasiru Sijia Jiang Yuetao Sun Dan Liu Chunyang Li

A novel polysaccharide from Cynanchum auriculatum Royle ex Wight was isolated, structurally characterized, and its antioxidant activity was evaluated. The crude extract was purified by ion exchange and size exclusion chromatography to obtain a homogeneous fraction, CAP2-1. CAP2-1 displayed a weight-average molecular mass of 184.17 kDa and is mainly composed of galactose, arabinose, and galacturonic acid. Structural analysis revealed that CAP2-1 is a highly branched acidic arabinogalactan-type polysaccharide with a backbone of →6)-β-D-Galp-(1→, →3,6)-β-D-Galp-(1→, and →4)-α-D-GalpA-(1→ units, and side chains enriched in α-L-arabino furanose residues. Ultrasonic degradation produced a lower-molecular-weight derivative, UCAP2-1, which exhibited significantly stronger free radical scavenging ability compared with CAP2-1 (p < 0.01). These findings suggest that molecular weight reduction enhances antioxidant properties by improving electron-donating capacity and accessibility to reactive sites. This study reveals the structure–antioxidant relationship of CAP2-1 and UCAP2-1 and highlights UCAP2-1 as a promising natural antioxidant.