Search Results (18)

The transport of chloride ions in concrete is often affected by electric fields, and its concentration distribution is generally evaluated using the Nernst–Planck equation. The Nernst–Planck theory can only effectively predict the mass electromigration in ideal porous media. However, under an electric field, cementitious materials still have a certain binding ability to chloride ions. This causes the transport model to have significant prediction errors, and the specific value of the electromigration coefficient cannot be accurately measured. This article systematically investigated the transfer rate of chloride ions in cementitious material under different current densities. An analytical solution of the Nernst–Planck equation containing an independent electromigration coefficient was presented, and its value was quantitatively measured and discussed. The results indicated that the relationship between the electromigration and the apparent diffusion coefficient of chloride ions needs to be fitted in segments corresponding to various electric voltage intensities; but the electromigration coefficient shows a highly linear relationship with the pure effective diffusion coefficient. This work can provide assistance and valuable data support for the evaluation of mass transport in non-ideal porous media, such as cementitious materials, using the Nernst–Planck theory. Full article

In the alkaline process for sodium stannate preparation, the oxidative dissolution of tin in the NaOH-H₂O₂ system originates from a spontaneous electrochemical reaction. This study elucidates the mechanism of ultrasound-enhanced tin dissolution in NaOH/H₂O₂ solutions from an electrochemical perspective, with particular emphasis on the tripartite regulatory effects of ultrasound on mass transfer, passivation suppression, and reaction pathway modulation. Electrochemical analysis indicates that ultrasound enhances mass transfer by disrupting the diffusion boundary layer, delays passivation, accelerates the exfoliation of the passive layer, and generates hydroxyl radicals that lower cathodic activation barriers. Under the action of 30 W ultrasound, the apparent diffusion coefficient of the solution increases and the passivation process of the tin sheet is delayed (the oxidation peak potential shift changes from −0.76 V to −0.70 V). After the passive layer is exfoliated by ultrasound, the charge transfer resistance decreases by 85.8% (from 8.09 ± 0.01 Ω to 1.15 ± 0.01 Ω). Ultrasound effectively overcomes the kinetic limitations imposed by the passivation layer through a triple synergistic mechanism involving mass transfer enhancement, passivation inhibition, and -OH path regulation. Full article

In this study, the adsorption of a textile dye from water onto activated carbon is considered and the results of our own experimental studies on adsorption equilibrium and kinetics are presented. The adsorption isotherm and kinetic curves were found to reflect the possibility of removing the dye from water by adsorption onto activated carbon. Kinetic studies were conducted using a fixed bed of adsorbent grains. The water and dye solution flowed through the column with the adsorbent. The main aim of this study was to determine diffusion coefficients and mass transfer coefficients. The values of the external mass transfer coefficient and external diffusion coefficient of the dye in water were calculated for different flow rates of the solution, i.e., for different external resistance values. The external diffusion coefficient was D_AB = 2.21·10⁻¹⁰ m²/s and the external mass transfer coefficient was between k_c = 4.813·10⁻⁸ m/s for the lowest solution velocity in the adsorber equal to 0.0693 m/s and k_c = 5.623·10⁻⁸ m/s for the highest velocity equal to 0.185 m/s. The internal diffusion coefficient and internal mass transfer coefficient, i.e., the coefficients of the transfer from the external surface of a grain to its interior, were determined with the use of the analytical solution of the diffusion and adsorption equation For the apparent solution velocity of 0.0693 m/s the internal diffusion coefficient was D_s = 0.57·10⁻¹⁰ m²/s and the internal mass transfer coefficient was k_s = 1.89·10⁻¹⁰ m/s. For the velocity of 0.163 m/s, the internal diffusion coefficient was D_s = 0.84·10⁻¹⁰ m²/s and the internal mass transfer coefficient was k_s = 9.00·10⁻¹⁰ m/s. The results of the calculations presented are a measure of the efficiency of a given adsorbent in a given system. The values obtained for the mass transfer coefficients can be used as data for further calculations of this process. Full article

This study investigates the coupled hygrothermal behavior of mycelium-based composites (MBCs) as a function of their microstructural organization, governed by fungal species, substrate type, additive incorporation, and treatment method. Eleven composite formulations were selected and characterized using a multi-scale experimental approach, combining scanning electron microscopy, dynamic vapor sorption, vapor permeability tests, capillary uptake measurements, and transient thermal conductivity analysis. SEM analysis revealed that Ganoderma lucidum forms dense and interconnected hyphal networks, whereas Trametes versicolor generates looser, localized structures. These morphological differences directly influence water vapor transport and heat conduction. Additive-enriched composites exhibited up to 21.8% higher moisture uptake at 90% RH, while straw-based composites demonstrated higher capillary uptake and free water saturation (up to 704 kg/m³), indicating enhanced moisture sensitivity. In contrast, hemp-based formulations with Ganoderma lucidum showed reduced sorption and vapor permeability due to limited pore interconnectivity. Thermal conductivity varied nonlinearly with temperature and moisture content. Fitting the experimental data with an exponential model revealed a moisture sensitivity coefficient thirty times lower for GHOP compared to VHOP, highlighting the stabilizing effect of a compact microstructure. The distinction between total and effective porosity emerged as a key factor in explaining discrepancies between apparent and functional moisture behavior. These findings demonstrate that hygric and thermal properties in MBCs are governed not by porosity alone, but by the geometry and connectivity of the internal fungal network. Optimizing these structural features enables fine control overheat and mass transfer, laying the groundwork for the development of high-performance, bio-based insulation materials. Full article

This paper presents research on the mass dispersion and adsorption of organics present in tap water on powdered activated carbon (PAC) in a two-layer filter column. The adsorption rate depends on the difference between the concentration of organics and the equilibrium concentration. In homogeneous flocculators with simultaneous adsorption on PAC, the concentration difference is lower than in a filter column with PAC. Therefore, the utilization of the PAC’s adsorption capacity in filters is higher than in homogeneous flocculators. PAC is introduced into the upper anthracite layer of a filter bed, while the bottom layer is a sand layer, which protects the underdrain system from becoming clogged with PAC particles. The sorbent wis introduced into the bed in the final phase of filter backwashing. The authors present a model of adsorption on PAC in a filter column. Both experiments and calculations confirmed a better utilization of PAC’s adsorption capacity in the filter column compared to its utilization in a homogeneous flocculator. Three criterion equations were developed using dimensionless numbers, Re, Pe and Nu, as well as two similarity moduli related to a sorbent apparent density and an adsorption coefficient. Additionally, a relationship between the Peclet number (Pe) and the Reynolds number (Re) as well as the similarity modulus for the sorbent apparent density were determined for the mass dispersion process. The relationship between the diffusive Nuselt number (Nu) and the Re number as well as the similarity modulus for the sorbent apparent density were determined for the parameter describing an adsorbate permeation rate across a water–sorbent interface. The impact of the Re number and the similarity modulus for the sorbent apparent density on the Henry constant was also investigated. The criterion equations can be used to determine the adsorption model parameters; they may be helpful in designing a filtration system supplemented with PAC. In the capillary velocity range $V_x^{*}$ ∈ ⟨0.15·10⁻²; 0.72·10⁻²⟩ m/s and with a change in the apparent density of the sorbent ${\rho }_{p,sorb}$ from 3000 to 12,000 g PAC/m³ of the bed, as a result of the experimental tests carried out, it was established that the actual coefficient of longitudinal dispersion $D_x^{*}$ varied in the range of 0.16·10⁻⁴ to 2.03·10⁻⁴ m²/s, the product of the constant mass transfer rate and the specific outer surface of sorbent $k\cdot a_m$ varied in the range of 2.23·10⁻⁷ to 1.70·10⁻⁶ (m/s)·(m²/g PAC), while the Henry constant Γ* varied in the range of 7.24 to 44.20 1/m³ of sorbent and the Henry constant Γ varied in the range of 0.0012 to 0.0019 m³ of water/g PAC. Full article

We investigated the reaction kinetics and initial chemical conditions in the production of silicon alloys, employing aluminum as the reductant for calcium silicate slag, to enhance process economics and scalability to industrial levels. The apparent kinetics and transient chemical conditions were studied by immersing solid aluminum into molten slag, allowing the reaction to proceed for varying durations without external agitation, before quenching the reaction for chemical and microscopic analyses of the resulting silicon alloy and slag. The majority of the conversion was observed within the first 15 s at 1650 °C, driven by significant chemical interactions and interfacial turbulence introduced upon aluminum immersion. For Al-SiO₂ stoichiometries ranging from 0.5 to 1.2, the slag phase reaction conformed to first-order kinetics during the initial two minutes, when it approached equilibrium. The mass transfer coefficients for Al₂O₃ were estimated at 1–2 × 10⁻⁴ m/s, comparable to those for SiO₂ and CaO. A constant mass transfer coefficient could not be established for stoichiometries of 1.6 and 2, as these deviated from the standard slag mass transfer relationship and did not adhere to established relationships. Despite near-complete reactions, alloy–slag mixing was extensive, decreasing with lower stoichiometry values. Full article

Disposal tunnels in geological repositories are ventilated continuously for over 50 years until their closure. Under these conditions, an unsaturated zone of mixed liquid and gas phases forms around the tunnels. Moreover, drying is assumed to progress from the host rock to the tunnels. To understand these drying processes, this study investigated the migration and precipitation of solutes via capillary forces during drying in packed columns using silica sand or glass beads as packed layers and X-ray CT analysis. In addition, the apparent permeability of a column packed with silica sand containing precipitation was examined using a flow experiment. The results indicate that the precipitation and accumulation of solutes were significant near the drying surfaces of the columns. The apparent mass transfer coefficient at a relatively early stage of the drying process indicates that the migration rate of solutes depends strongly on the capillary forces during the drying process. Furthermore, the apparent permeability of the columns with precipitation decreased significantly. These indicate that the precipitation and accumulation of solutes with drying in the groundwater reduce the porosity and permeability, and the advection of groundwater around the repository may be suppressed. Full article

Given the demand for extremely low sulfur content in 5 wt% Si high-silicon austenitic stainless steel (SS-5Si), smelting utilizes a slag composition of CaF₂-CaO-Al₂O₃-MgO-SiO₂ with a basicity of 1 to 3, Al₂O₃ content ranging from 2.04 to 9.61%, and CaF₂ content between 20.8 and 31.62%. Experiments designed to investigate the sulfur content in molten steel at temperatures of 1773 K, 1823 K, and 1873 K over durations of 1, 5, 10, 15, and 30 min, under varying slag compositions, corroborated with a theoretically derived model hypothesizing a “rate-controlling” step in mass transfer, revealed that the mass transfer of sulfur within the molten steel was determined to be the rate-controlling step (RCS) in the (CaO) + [S] = (CaS) + [O] reaction kinetics, and the variability of the mass transfer coefficient of sulfur, k_S,m, in the molten steel ranged from 1.04 × 10⁻⁵ m∙s⁻¹ to 2.24 × 10⁻⁵ m∙s⁻¹. Based on the temperature dependency of k_S,m, the apparent activation energy for the desulfurization reaction was estimated to be 96.03 kJ/mol. Considering the slag components, the binary basicity, denoted as R, exerted an overriding influence on the process of desulfurization. At a basicity of 1, the sulfur content within the liquid steel was reduced, from 22 ppm to 11 ppm within a time span of 30 min. In contrast, an increase in the basicity to a value of 3 showed a significant consequence: over an identical temporal duration of 30 min, the sulfur content was drastically reduced to 2.2 ppm. By contrast, an initial surge in desulfurization rates is observed within the first five minutes, attributable to relatively lower concentrations of Al₂O₃ and higher levels of CaF₂. Subsequently, these parameters exert no significant influence on the kinetics of the desulfurization process. Full article

The paper compares and evaluates the influence of the presence of perforations on the sound absorption coefficient (SAC) of a negative stiffness metamaterial based on a foamed ceramic geopolymer. Chemical–physical, microstructural, dynamic–mechanical, and sound characterisations are presented. A rigid, lightweight geopolymeric porous material has been prepared using an inorganic/organic monomeric mixture containing oligomeric sialates and siloxanes foamed with aluminium powder. This process results in an amorphous rigid light foam with an apparent 180 Kg/m³ density and a 78% open-pore. The viscoelastic characterisation by dynamic mechanical analysis (DMA) carried out from 10⁻³ to 10³ Hz indicates the behaviour of a mechanical metamaterial with negative stiffness enabling ultrahigh energy absorption at straining frequencies from 300 to 1000 Hz. The material loss factor (the ratio of dissipative/elastic shear moduli) is about 0.03 (essentially elastic behaviour) for frequencies up to 200 Hz to suddenly increase up to a value of six at 1000 Hz (highly dissipative behaviour). The corresponding storage and loss moduli were 8.2 MPa and 20 MPa, respectively. Impedance tube acoustic absorption measurements on perforated and unperforated specimens highlighted the role of perforation-resonant cavities in enhancing sound absorption efficiency, particularly within the specified frequency band where the mass of the negative stiffness foamed geopolymer matrix magnifies the dissipation effect. In the limits of a still exploratory and comparative study, we aimed to verify the technological transfer potentiality of using architected metamaterials in sustainable building practices. Full article

4-Nitroaniline (4NA) is a common organic pollutant that is released into the environment during the manufacture and processing of a wide variety of industrial products. This article describes the use of an emulsion liquid membrane process to remove 4NA from aqueous solutions using a type 1 facilitated transport mechanism. Optimization of the removal process was carried out by analyzing the efficiency of 4NA removal from the feed phase and the initial apparent feed/membrane fluxes and permeabilities under different experimental conditions. The kinetics of the removal process was analyzed using a simplified mass transfer model involving an empirical mass transfer coefficient calculated from experimental data, assuming that the concentrations of 4NA in the external aqueous phase and in the internal w/o emulsion are uniform. The results show that there is a very good fit between the experimental and model data and that the variation in the values of the overall mass transfer coefficients with the experimental conditions coincides with that of the removal efficiency mentioned above. The transport mechanism was studied by identifying the rate-controlling step of the removal process, using models described for adsorption processes, due to the strong parallelism between the transport mechanisms in adsorption and emulsion liquid membrane processes. Full article

After the atmospheric hydrochloric acid leaching method is used to treat laterite ore and initially purify it, the extract that results often contains a significant amount of Fe²⁺ impurities. A novel metallurgical process has been proposed that utilizes microbubble aeration to oxidize Fe²⁺ ions in laterite hydrochloric acid lixivium, facilitating subsequent separation and capitalizing on the benefits of microbubble technology, including its expansive specific surface area, negatively charged surface attributes, prolonged stagnation duration, and its capacity to produce active oxygen. The study examined the impacts of aeration aperture, stirring speed, oxygen flow rate, pH value, and reaction temperature. Under optimized experimental conditions, which included an aeration aperture of 0.45 µm, stirring at 500 rpm, a bubbling flow rate of 0.4 L/min, pH level maintained at 3.5, and a temperature range of 75–85 °C, the oxidation efficiency of Fe²⁺ surpassed 99%. An analysis of the mass transfer process revealed that microbubble aeration markedly enhances the oxygen mass transfer coefficient, measured at 0.051 s⁻¹. The study also confirmed the self-catalytic properties of Fe²⁺ oxidation and conducted kinetic studies to determine an apparent activation energy of 399 kJ/mol. At pH values below 3.5, the reaction is solely governed by chemical reactions; however, at higher pH values (>3.5), both chemical reactions and oxygen dissolution jointly control the reaction. Full article

The utilization of metallurgical waste heat for urban sludge drying and dewatering not only affects the subsequent cost of sludge treatment but also provides a pathway for the rational utilization of metallurgical waste heat. The influence of different experimental conditions on sludge drying characteristics, such as drying temperature and thickness, was analyzed based on metallurgical waste heat. Based on the analysis and evaluation of the drying kinetics parameters of commonly used drying mathematical models, a modified Midilli drying kinetic model is proposed. The kinetic parameters and effective diffusivity of sludge drying were analyzed in three stages of sludge drying: rising rate, constant rate, and falling rate. By utilizing the Arrhenius equation, the relationship between the effective diffusion coefficient and thermodynamic temperature is established, revealing the apparent activation energies for the three stages of urban sludge drying as 29.772 kJ·mol⁻¹, 37.129 kJ·mol⁻¹, and 39.202 kJ·mol⁻¹, respectively. This is closely related to the migration, diffusion, and mass transfer resistance of sludge moisture, indicating that the thickness of sludge accumulation affects the drying time of sludge during the treatment of municipal sludge. Full article

With the growing worldwide attention towards environmental protection, the rational utilization of rice straw (RS) has gradually attracted the attention of scholars. This paper innovatively puts forward a solution for rational utilization of RS. A rice straw fiber concrete (RSFC) with good physical and mechanical properties and a rice straw concrete-light steel keel wall panel (RS-LSWP) with low comprehensive heat transfer coefficient and inconspicuous cold bridge phenomenon was designed. Firstly, the preparation method and process of RSFC is described in detail. Then, the physical and mechanical properties of RSFC, such as strength, apparent density, and thermal conductivity were tested. Finally, the thermal properties of the four new types of cold-formed thin-wall steel panels were analyzed using finite element simulation. The results show that the RSFC with a straw length of 5 mm, mass content of 12%, and modifier content of 1% is the most suitable for RS-LSWP. The standard compressive strength, tensile strength, and thermal conductivity of the RSFC are 2.2 MPa, 0.64 MPa, and 0.0862 W/(m·K), respectively. The wall panels with antitype C keel have a low comprehensive heat transfer coefficient and the best insulation effect. This study innovatively provides a technical method for the rational utilization of RS, promotes the application of RS and other agricultural wastes in building materials and the development of light steel housing. Full article

Phytoremediation of arsenic-contaminated water was successfully conducted by means of the perennial fern Pteris vittate, which is an arsenic-hyperaccumulator plant able to grow in hydroponic cultures. In order to avoid the costs linked to the disposal of As-contaminated biomass, in this work, Pteris vittata waste roots were tested as a low-cost bio-adsorbent for the removal of methylene blue (MB) from water in a fixed-bed adsorption configuration. As a matter of fact, methylene blue can negatively impact the growth and health of algae and plants by blocking light from reaching them in water, which can alter their normal biological processes. Previous works have already shown the potentiality of such material toward the uptake of methylene blue; however, all the studies conducted were just focused on batch-mode experiments. In this work, column runs were carried out at 20 °C, evaluating the bed void fraction for each test and hence estimating the apparent density of the material (300 g/L). The breakthrough curves collected were fitted by means of a mathematical model based on the linear driving force (LDF) approximation to obtain information on the mass transfer mechanism occurring in the system. A relation for the product between the LDF mass transfer coefficient and the solid specific surface ($k_{LDF}{a}_s$) with respect to the Reynolds ($Re$) dimensionless number was obtained ($k_{LDF}{a}_s=0.45Re$). The range of validity of such expression was $Re<0.025$. Its applicability was deeply discussed: in such conditions, the technology is ready to be tested at larger scales. Full article

Conventional ultrasonography represents the mainstay of testis imaging. In cases in which ultrasonography is inconclusive, scrotal MRI using a multiparametric protocol may be used as a useful problem-solving tool. MRI of the scrotum is primarily recommended for differentiating between benign and malignant testicular masses when sonographic findings are ambiguous. This technique is also accurate in the preoperative local staging of testicular tumors and, therefore, is recommended in patients scheduled for testis-sparing surgery. In addition, MRI may provide valuable information regarding the histological characterization of testicular germ-cell tumors, in selected cases. Scrotal MRI may also help in the differentiation between testicular germ-cell neoplasms and non-germ-cell neoplasms. Axial T1-weighted imaging, axial and coronal T2-weighted imaging, axial diffusion-weighted imaging, and coronal subtracted dynamic contrast-enhanced imaging are the minimum requirements for scrotal MRI. A variety of MRI techniques—including diffusion tensor imaging, magnetization transfer imaging, proton MR spectroscopy, volumetric apparent diffusion coefficient histogram analysis, and MRI-based radiomics—are being investigated for testicular mass characterization, providing valuable supplementary diagnostic information. In the present review, we aim to discuss clinical indications for scrotal MRI in cases of testicular tumors, along with MRI findings of common testicular malignancies. Full article