Search Results (607)

Aluminum–chromium slag (ACS), a by-product of aluminothermic reduction, which is used to produce metallic chromium and its alloys, contains toxic, carcinogenic hexavalent chromium (Cr(VI)). Therefore, improper ACS utilization may severely harm human health and the environment. This study analyzed the Cr(VI) contents, leaching characteristics, and surface concentrations in ACS and four industrially utilized products derived from it (fused alumina for refractories, ferrochromium, aluminum–chromium bricks, and high-chromium bricks). A risk assessment framework was established to evaluate their human health and environmental risks. Results showed 111 mg/kg Cr(VI) in the ACS, with its leaching concentration (7.8 mg/L) exceeding China’s hazardous waste standard. The Cr(VI) contents in the products were low (from <2 mg/kg to 16 mg/kg), and their maximum leaching concentration was below the detection limit (<0.004 mg/L). Furthermore, the four products were found to have acceptable levels of human health risk (<10⁻⁵ carcinogenic risk and <1 noncarcinogenic hazard quotient) under two risk assessment methods (particle-contact- and surface-contact-based methods). Additionally, the predicted concentration of leached Cr(VI) in groundwater (0.008 mg/L) was below the drinking water standard (0.05 mg/L). Cr(VI) limit standards for the products were then proposed based on the risk assessment (≤31 mg/kg content, ≤0.189 mg/m² surface concentration, and ≤0.259 mg/L leaching concentration). Overall, these results may provide a reference for the safe utilization and risk management of ACS and other solid wastes. Full article

Plastic remains a cheap material for numerous uses in households, industries, and engineering; however, it disintegrates in aquatic ecosystems to form smaller particles termed microplastics. Microplastics (MPs) have become a cause for concern due to their persistence and potential effects on freshwater ecosystems. Moreover, the toxicity of microplastics can be achieved through different mechanisms, including physical blockage and additive leaching, or they can function as vectors for other chemical pollutants. Microplastics were found to provide a growing surface for microbial communities, forming a biofilm termed the plastisphere. Microplastic pollution seems to need urgent attention globally; however, the comparability of results becomes a challenge due to the different techniques employed by different researchers. Moreover, the complete removal of MPs has proven to be an impossible task. This review explored MP occurrence in freshwater ecosystems, the role of microbial communities in the dynamics of microplastics, removal techniques, strategies for reduction in the environment, and their effect on freshwater ecosystems. Moreover, techniques to reduce microplastic release, such as recycling, plastic–fuel conversion, and biodegradable plastics, are explored. The review provides recommendations for reducing microplastic release and removal in freshwater ecosystems. This review stresses existing gaps to explore going forward in addressing microplastic pollution and possible removal techniques. Full article

Reducing nitrogen (N) fertilizer input while sustaining maize yield and alleviating nitrogen leaching is a significant challenge due to economic and practical feasibility, as well as the environmental friendliness of this process. However, it remains unclear whether reducing nitrogen by using a blend of slow/controlled-release nitrogen fertilizer (SCRNF) with urea at an equal nitrogen rate can achieve the desired yield and mitigate nitrogen leaching. A field experiment consisting of four treatments (240 kg·N·hm⁻², 100% urea, CK; 240 kg·N·hm⁻², 50% N from urea and 50% N from SCRNF, N100%; 192 kg·N·hm⁻², 50% N from urea and 50% N from SCRNF under 20% N reduction, NR20%; 144 kg·N·hm⁻², 50% N from urea and 50% N from SCRNF under 40% N reduction, NR40%) was conducted in Shanxi from 2019 to 2021. In this study, we explored the effects of a mixture of SCRNF and urea on grain yield, yield components, main agronomic traits, nitrogen partial factor productivity, and content of nitrate/ammonium nitrogen in soil in maize under decreasing amounts of nitrogen fertilization. The results showed that the mixture of SCRNF and urea can improve spring maize yield under reduced nitrogen input, with its yield and yield component factors generally performing better than those of the control. The yield of the NR20% treatment was highest in 2020 and 2021, increasing by 8.8% and 11.7% over CK, respectively; the NR20% and NR40% treatments had no significant impact on the main agronomic traits of spring maize, such as plant height, leaf area, shoot biomass, and SPAD value of the ear leaf, compared with CK; the NR20% and NR40% treatments significantly (p < 0.05) enhanced nitrogen partial factor productivity but reduced nitrate and ammonium nitrogen in 0~200 cm soil over the three years compared with CK. Therefore, reducing nitrogen input by 20% with 50% N from urea and 50% N from biodegradable film-coated urea was an appropriate nitrogen fertilizer management measure for mitigating environmental risks without compromising maize yield in North China. Full article

Laboratory and industrial tests were conducted to study the impact of grinding media material on key indicators such as grinding product particle size, sodium cyanide consumption, gold recovery rate, unit power consumption, and ball consumption. Laboratory test results indicate that the reasonable mixing of ceramic and steel balls can achieve an increase of more than 2.8% in the fineness of the grinding product (−0.038 mm), an increase of 0.3% in the gold recovery rate, and a decrease of 1.3 kg/t in the consumption of sodium cyanide. Industrial trial studies indicate that, compared to the traditional steel ball scheme, using a ceramic ball to steel ball mass ratio of 3:1 under conditions of processing 50,000 tons of gold concentrate annually can save a total of 1.31 million yuan in annual ball consumption, electricity consumption, and cyanide consumption costs. Additionally, the improved recovery rate generates an additional economic benefit of 3.63 million yuan, resulting in an annual comprehensive economic benefit increase of 4.94 million yuan. In summary, in gold cyanide leaching grinding, the mixture ratio between ceramic balls and steel balls demonstrates significant potential for energy conservation, cost reduction, and efficiency enhancement, providing a theoretical basis and technical support for subsequent process optimization and green gold extraction. Full article

The calciothermic reduction slag (CRS) generated in heavy rare earth metal production, is rich in rare earth elements (REE) and highly amenable to recovery. In the present study, the CRS was treated with a H₂SO₄ roasting–water leaching method for the recovery of REEs. The feasibility of this process was confirmed by thermodynamic analysis. Key roasting and leaching factors governing the leaching efficiency of REE were identified and optimized. The maximum REE extraction efficiency reached 94.65% under the optimal conditions: roasting at 150 °C for 240 min with 15 mL of H₂SO₄, followed by water leaching at 20 °C for 60 min at a liquid–solid ratio of 15:1. Results of XRD, SEM, and EDS revealed that the REEs in the CRS were transformed into water-soluble rare earth sulfates after roasting. In the leaching process, the rare earth sulfate is efficiently extracted, whereas CaSO₄ has low solubility in water. A CaSO₄ product with a 98.10% purity was obtained with a calcium recovery of 90.79%, and the removal rate of fluorine in the CRS was 99.99%. The leaching kinetics of the REEs follow a diffusion plus interfacial transfer model with an apparent activation energy of –46.45 kJ·mol⁻¹. This study demonstrates that sulfation roasting–water leaching is a viable route for the comprehensive utilization of CRS. Full article

Ti-bearing blast furnace slag (TBS), a byproduct of vanadium–titanium magnetite smelting, serves as an important secondary resource for titanium recovery. However, the complex mineralogical composition and finely dispersed nature of titanium in TBS present significant challenges for efficient extraction. This review systematically examines four major titanium extraction routes: hydrometallurgical leaching, pyrometallurgical smelting, molten salt electrolysis, and selective precipitation, focusing on their limitations and recent improvements. For instance, conventional acid leaching suffers from acid mist release, a colloidal formation that hinders titanium recovery, and waste acid pollution. The adoption of concentrated sulfuric acid roasting activation effectively suppresses acid mist emission and prevents colloidal generation. Pyrometallurgical approaches are hampered by high energy consumption and substantial carbon emissions, which can be alleviated through the use of gaseous reductants to enhance reaction efficiency and reduce environmental impact. Molten electrolysis faces issues such as polarization and undesirable dendritic deposition; these are mitigated by employing liquid metal cathodes integrated with vacuum distillation to achieve high-purity titanium products. Selective precipitation struggles with strict crystallization conditions and low separation efficiency, though advanced techniques like supergravity separation show improved extraction performance. We propose an integrated technical strategy termed “Online conditioning driven by waste heat-mineral phase reconstruction-directional crystallization-optimized liberation.” This approach utilizes the inherent waste heat of slag combined with electromagnetic stirring to enhance homogeneity and promote efficient titanium recovery, offering a sustainable and scalable solution for industrial TBS treatment. Full article

Enhancing cobalt recovery from complex low-grade copper–cobalt oxide ores represents a pressing industrial challenge in the Democratic Republic of the Congo (DRC). This study comparatively examined the sulfuric acid leaching behaviors of two copper–cobalt oxide ores with similar mineralogical characteristics and developed a synergistic blending strategy to enhance cobalt recovery. At an endpoint pH of 1.5, both ores achieved high copper extraction (>90%). However, the reductive Re-ore attained >75% Co leaching efficiency, contrasting sharply with the oxidative Ox-ore’s limited 22% recovery. This disparity was attributed to refractory high-valent cobalt phases in Ox-ore requiring a reductive environment. Blending Re-ore with Ox-ore generated a pronounced synergistic effect, progressively lowering the slurry potential with increasing Re-ore mass ratio. At 50% Re-ore incorporation, the leaching efficiency of cobalt from Ox-ore surged from 22.5% to 76% owing to the decrease in slurry potential to 557 mV, substantially exceeding proportional predictions. Residue characterizations confirmed that cobalt phases in Ox-ore were solubilized in the reductive environment facilitated by the residual sulfide phase in Re-ore. Enhanced dissolution of Fe²⁺ and Mn²⁺ further correlated with potential-dependent cobalt recovery. This ore-blending strategy provides a cost-efficient alternative to chemical reductants by leveraging intrinsic ore properties to optimize cobalt extraction from challenging oxidized ores. Full article

With the increasing severity of cadmium (Cd) contamination in soil and its persistent toxicity, developing efficient remediation methods has become a critical necessity. In this study, sodium borohydride (NaBH₄) and tea polyphenols (TP) were employed as reducing agents to synthesize biochar (BC)-supported nanoscale zero-valent iron (nZVI), denoted as BH₄-nZVI/BC and TP-nZVI/BC, respectively. The effects of dosage, pH, and reaction time on Cd immobilization efficiency were systematically investigated. Both composites effectively stabilized Cd, significantly reducing its mobility and toxicity. Toxicity Characteristic Leaching Procedure (TCLP) results showed that Cd leaching concentrations decreased to 8.23 mg/L for BH₄-nZVI/BC and 4.65 mg/L for TP-nZVI/BC, corresponding to performance improvements of 29.9% and 60.5%. The immobilization process was attributed to the reduction of Cd(II) into less toxic species, together with adsorption and complexation with oxygen-containing groups (-OH, -COOH, phenolic) on biochar. TP-nZVI/BC exhibited superior long-term stability, while maintaining slightly lower efficiency than BH₄-nZVI/BC under certain conditions. Microbial community analysis revealed minimal ecological disturbance, and TP-nZVI/BC even promoted microbial diversity recovery. Mechanistic analyses further indicated that tea polyphenols formed a protective layer on nZVI, which inhibited particle agglomeration and oxidation, reduced the formation of iron oxides, preserved Fe⁰ activity, and enhanced microbial compatibility. In addition, the hydroxyl and phenolic groups of tea polyphenols contributed directly to Cd(II) complexation, reinforcing long-term immobilization. Therefore, TP-nZVI/BC is demonstrated to be an efficient, sustainable, and environmentally friendly amendment for Cd-contaminated soil remediation, combining effective immobilization with advantages in stability, ecological compatibility, and long-term effectiveness. Full article

Soil secondary salinization is a major limiting factor of sustainable agricultural production in arid and semi-arid irrigation zones, yet predictive tools for regional water–salt dynamics remain limited. The Yichang Irrigation District, located within the Hetao Irrigation Area, has experienced persistent salinity challenges due to shallow groundwater tables and intensive irrigation. In this study, we aimed to simulate long-term soil water–salt dynamics in the Yichang Irrigation District and evaluate the effectiveness of different engineering and management scenarios using the SaltMod model. Field monitoring of soil salinity and groundwater levels during summer and fall (2022–2024) was used to calibrate and validate SaltMod parameters, ensuring accurate reproduction of seasonal soil salinity fluctuations. Based on the calibrated model, ten-year scenario simulations were conducted to assess the effects of changes in soil texture, irrigation water quantity, water quality, rainfall, and groundwater table depth on root-zone salinity. Our results show that under baseline management, soil salinity is projected to decline by 5% over the next decade. Increasing fall autumn leaching irrigation further reduces salinity by 5–10% while conserving 50–300 m³·ha⁻¹ of water. Sensitivity analysis indicated groundwater depth and irrigation water salinity as key drivers. Among the engineering strategies, drainage system improvement and groundwater regulation achieved the highest salinity reduction (15–20%), while irrigation regime optimization provided moderate benefits (~10%). This study offers a quantitative basis for integrated water–salt management in the Hetao Irrigation District and similar regions. Full article

This study investigates the use of preliminary thermochemical activation in a NaHCO₃ solution under elevated pressure and temperature to modify the chemically stable and hard-to-process phase composition of various mineral raw materials and improve the recovery of valuable components. The method was tested on various types of mineral raw materials, including slag from the reductive smelting of red mud from alumina production prior to acid leaching, ash before chemical beneficiation, gibbsite–kaolinite bauxite prior to gravity separation, and nephelines, for which the sintering process was replaced with chemical beneficiation. The slag from the reductive smelting of red mud was also tested before acid leaching. The activation of slag enhanced tricalcium silicate formation lead to leaching recoveries of ~96% for rare earth elements, ~92% for TiO₂, ~98% for CaO and Al₂O₃, and 50% for Fe₂O₃, compared to much lower values without activation. With ash, activation eliminated the sillimanite and hedenbergite phases, increased mullite and free silica, and formed calcite, resulting in a 15–20% higher silica recovery. With gibbsite–kaolinite bauxite, activation altered kaolinite, siderite, quartz, and hematite contents; eliminated calcium silicate; and improved the silicon modulus of the sand fraction by 35.9% during gravity beneficiation. For nepheline ore, activation promoted the formation of albite and hydrosodalite, eliminated corundum and andradite, and increased silica recovery from 33.58% to 59.6%. These results demonstrate that thermochemical activation effectively transforms mineral structures and significantly improves the efficiency of subsequent beneficiation processes. Full article

WSNs consist of numerous energy-constrained Sensor Nodes (SNs), making energy efficiency a critical challenge. This paper presents a novel multipath routing model designed to enhance network lifetime by simultaneously optimizing energy consumption, node connectivity, and transmission distance. The model employs an Improved Particle Swarm Optimization (IPSO) algorithm to dynamically determine the optimal weight coefficients of a cost function that integrates three parameters: residual energy, link reliability, and buffer capacity. A compressed Bloom filter is incorporated to improve packet transmission efficiency and reduce error rates. Simulation experiments conducted in the NS2 environment show that the proposed approach significantly outperforms existing protocols, including Reinforcement Learning Q-Routing Protocol (RL-QRP), Low Energy Adaptive Clustering Hierarchical (LEACH), On-Demand Distance Vector (AODV), Secure and Energy-Efficient Multipath (SEEM), and Energy Density On-demand Cluster Routing (EDOCR), achieving a 7.45% reduction in energy consumption and maintaining a higher number of active nodes over time. Notably, the model sustains 19 live nodes at round 800, whereas LEACH and APTEEN experience complete node depletion by that point. This adaptive, energy-aware routing strategy improves reliability, prolongs operational lifespan, and enhances load balancing, making it a promising solution for real-world WSN applications. Full article

Coal ash is a promising secondary resource for rare earth element (REE) recovery, yet efficient processing under environmentally benign conditions remains challenging. This study demonstrates that tartaric acid, when combined with MgSO₄ as a salt additive, enables effective extraction of light REEs (La, Ce, Nd). REE recoveries improved from ~40% without salt to nearly 65% under optimized conditions. Kinetic modeling indicated a surface-reaction–controlled mechanism with activation energies of 20–22 kJ/mol, consistent with SEM evidence of particle erosion and size reduction. These findings highlight the potential of organic-salt leaching systems as alternatives to mineral acid processes, offering both effective REE recovery and reduced environmental impact. Full article

In line with circular economy principles and the reduction of primary material exploitation, waste-to-energy (WtE) by-products such as bottom ash (BA) are increasingly being used as raw materials in cement and ceramics manufacturing. However, it is critical to verify that the final product presents not only adequate technical properties but also that it does not pose negative impacts to the environment and human health during its use. This study investigates the environmental compatibility of the use of ceramic porcelain stoneware tiles manufactured with BA as partial replacement of traditional raw materials, with a particular focus on the leaching behavior of the tiles during their use, and also after crushing to simulate their characteristics at their end of life. To evaluate the latter aspect, compliance leaching tests were performed on crushed samples and compared with Italian End-of-Waste (EoW) thresholds for the use of construction and demolition waste as recycled aggregates. Whereas, to assess the environmental compatibility of the tiles during the utilization phase, a methodology based on the application of monolithic leaching tests to intact tiles, and the evaluation of the results through multi-scenario human health risk assessment and the analysis of the main mechanisms governing leaching at different stages, was employed. The results of the study indicate that the analyzed BA-based tiles showed no significant increase in the release of potential contaminants compared to traditional formulations and fully complied with End-of-Waste criteria. The results of the monolith tests used as input for site-specific risk assessment, simulating worst-case scenarios involving the potential contamination of the groundwater, indicated negligible risks to human health for both types of tiles, even considering very conservative assumptions. As for differences in the release mechanisms, tiles containing BA exhibited a shift toward depletion-controlled leaching and some differences in early element release compared to the ones with a traditional formulation. Full article

Aluminothermic reduction is gaining renewed interest as an alternative processing route for the circular economy. Aluminium is produced electrochemically in the Hall–Héroult process with minimal CO₂ emissions if electricity is sourced from non-fossil fuel energy sources. The Al₂O₃ product from the aluminothermic reduction process can be recycled via hydrometallurgy, with leaching as the first step. NaAlO₂ is a water-leachable compound that forms a pathway for recycling Al₂O₃ with hydrometallurgy. In this work, a suitable slag formulation is applied in the aluminothermic reduction of manganese ore to form a Na₂O-based slag of high Al₂O₃ solubility to effect good alloy–slag separation. The synergistic effect of added chromium metal as a collector metal is illustrated with an increased alloy yield at 68%, from 43% without added Cr. The addition of small amounts of carbon reductant to MnO₂-containing ore ensures rapid pre-reduction to MnO. This approach negates the need for a pre-roasting step. The alloy and slag chemical analyses are compared to the thermochemistry-predicted phase chemistry. The alloy consists of 57% Mn, 18% Cr, 18% Fe, 3.4% Si, 1.5% Al, and 2.2% C. The formulated slag exhibits high Al₂O₃ solubility, enabling effective alloy–slag separation, even at an Al₂O₃ content of 55%. Full article

The growing demand for lithium-ion batteries (LIBs) has led to an urgent need for sustainable recycling strategies for spent cathode materials. In this study, a mechanochemical approach was developed for the recovery of lithium and cobalt from end-of-life LiCoO₂ cathodes using high-energy ball milling. For the first time, aluminum and carbon were employed as internal reducing agents, facilitating the in situ decomposition of LiCoO₂ into CoO, Li₂O, and metallic Co. X-ray diffraction analysis confirmed significant structural disorder, phase transitions, and the formation of CoO, AlCo, and spinel-like CoAl₂O₄. The Taguchi method was applied to optimize milling parameters, identifying 800 rpm, 60 min, and a ball-to-powder ratio of 50:1 as the most effective conditions for structural activation. Subsequent ammonia leaching under fixed conditions (3.0 M NH₃·H₂O, 1.0 M (NH₄)₂CO₃, 60 °C, 25 mL/g, 6 h) demonstrated high recovery efficiencies: up to 94.6% for lithium and 83.7% for cobalt in the best-performing samples. These results highlight the synergistic benefits of mechanical activation and reductant-assisted phase engineering for enhancing metal recovery. The proposed method offers a simple, scalable, and eco-friendly route for the hydrometallurgical recycling of LIB cathodes without requiring extensive chemical pretreatment. Full article