ABSTRACT Low-grade brucite is a promising magnesium-silicon resource, but its complex composition and high impurity content severely limit its application. This study developed an integrated ammonia distillation-acid leaching process to achieve the synergistic recovery of high-purity magnesium hydroxide and amorphous silica from low-grade brucite. The optimal ammonia distillation conditions were determined as an ammonia-to-magnesium molar ratio of 3:1, reaction temperature of 105 °C and duration of 4 h, enabling efficient Mg²+ leaching with a concentration of 0.9 mol/L. Ammonia precipitation at 50 °C yielded hexagonal flake magnesium hydroxide with uniform particle size and high purity, whose growth mechanism was clarified by BFDH model simulation. The silicon-rich residue was treated by acid leaching under optimised parameters (stirring rate 500 r/min, sulfuric acid concentration 4 mol/L, temperature 353 K), producing amorphous silica with purity ≥98%, specific surface area ≥300 m²/g and particle size ≤45 μm. Kinetic analysis indicated that the acid leaching process followed a chemical reaction mixed-control model with an apparent activation energy of 59.66 kJ/mol. This process realises the high-value utilisation of low-grade brucite, providing a sustainable solution for similar mineral resources and conforming to the principles of circular economy.

Biofuel production from biomass sources remains a key area of research, aimed at reducing reliance on fossil fuels and promoting environmental sustainability. This study investigates the conversion of used cooking oil (UCO) into biogasoline via catalytic hydrocracking, employing sulfated mesoporous silica dispersed with nickel as the catalyst. Mesoporous silica was synthesized using tetraethyl orthosilicate (TEOS) and NaHCO₃ as the template, followed by a hydrothermal method to introduce sulfate groups and nickel metal. Among the synthesized catalysts, SMS-2 exhibited the highest acidity across varying sulfuric acid concentrations, while 1 Ni/SMS-2 demonstrated superior acidity compared to other nickel loadings. The SiO₂, SMS-2, and 1 Ni/SMS-2 catalysts were evaluated for UCO hydrocracking in a semi-batch double-furnace reactor operated at an optimum temperature of 550 °C for 2 h, with a hydrogen flow rate of 20 mL min⁻¹ under atmospheric pressure. Modifying mesoporous silica with sulfuric acid and nickel significantly enhanced its catalytic performance, with the 1 Ni/SMS-2 catalyst achieving the highest liquid product yield (66.10%) and gasoline fraction (35.47%) at an optimum catalyst-to-feed ratio of 1:100 (w/w). Notably, the resulting biogasoline exhibited a calorific value comparable to commercial gasoline and was free of aromatic hydrocarbons, indicating the potential for cleaner combustion. This study provides valuable insights into the effectiveness of mesoporous silica-based catalysts, highlighting their acid site modulation capabilities for efficiently transforming waste into high-value fuels. Copyright © 2026 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Seaweed bioactive extraction generates de-extracted residual solids that remain carbohydrate-rich but are often underutilized. This study developed an integrated valorization route for Gracilaria fisheri spent biomass to produce fermentable sugars for β-carotene production by Rhodotorula paludigena CM33. Reducing sugar production was optimized using response surface methodology (Box–Behnken design) by varying reaction time, sulfuric acid concentration, and biomass loading at 90 °C. The predicted optimum (47.39 min, 2.50% (w/v) H2SO4, and 7.13% (w/v) biomass) yielded 22.41 g/L reducing sugars and was validated experimentally at 22.22 ± 0.19 g/L, indicating that the model reliably predicted reducing sugar production. The optimized condition was scaled up in a 22 L bioreactor with sequential acid hydrolysis followed by enzyme-assisted hydrolysis, increasing reducing sugars from ~30 to ~40 g/L. FTIR and SEM analyses indicated progressive modification of the carbohydrate matrix across processing stages. Batch cultivation of R. paludigena on the hydrolysate showed that ammonium sulfate supplementation significantly increased biomass, whereas β-carotene titers were not significantly different. Repeated-batch operation on non-supplemented hydrolysate sustained production over four cycles with β-carotene titers of 13.75–17.27 mg/L, demonstrating the operational feasibility of the hydrolysate-based system. Overall, this work demonstrates a practical seaweed biorefinery approach to upgrade G. fisheri spent biomass into sugars and carotenoid-rich yeast biomass.

This work addresses the preparation of V3.5+ electrolyte for vanadium redox flow batteries (VRFBs) by proposing an efficient paired electrosynthesis strategy, combining it with the synthesis of the high-value-added chemical p-chlorobenzaldehyde (PCAD). Traditional methods for preparing V3.5+ electrolyte suffer from issues like impurity introducing and low energy utilizing, while the hydrogen reduction reaction at the cathode in PCAD synthesis has low value. To solve these problems, this work designed and constructed a paired electrosynthesis system based on an electrochemical microchannel reactor: precisely reducing VOSO4 to V3.5+ electrolyte at the cathode, while simultaneously electro-oxidizing Mn2+ to Mn3+ at the anode, which subsequently oxidizing p-chlorotoluene (PCT) to synthesize PCAD. The effects of current density, sulfuric acid concentration, and reactant ratio on reaction efficiency were systematically investigated. Results show that the total vanadium valence state of the cathodically prepared V3.5+ electrolyte stabilized at 3.50 ± 0.02, the yield of anodically synthesized PCAD was 35.51%, the total current efficiency of the paired electrosynthesis system reached 178.8%, and the system demonstrated good repeatability and stability. This study provides a new approach for the green and efficient preparation of VRFB electrolytes and the electrosynthesis of high-value chemicals.

ABSTRACT This study aims to develop an economical, facile, and efficient approach for the recovery and reuse of Fenton sludge (FS) by proposing an in-situ reutilisation strategy that integrates acid leaching with micron-sized zero-valent iron (mZVI) reduction. Given the high iron content of FS (50.68%), single-factor experiments were performed to investigate the influence of critical parameters in acid leaching (liquid-to-solid ratio, sulfuric acid concentration, and acid leaching time) and mZVI reduction (mZVI/Fe3+ (mol/mol), reaction time, and stirring speed). Furthermore, response surface methodology was applied to optimise the process parameters. The optimisation results showed that the optimal acid leaching conditions were a liquid-to-solid ratio of 2.1, a sulfuric acid concentration of 6.2 mol/L, and an acid leaching time of 32 min, achieving a total iron leaching efficiency of 94.24%. For mZVI reduction, the optimal conditions were an mZVI/Fe3+ of 2.15, a reaction time of 134.4 min, and a stirring speed of 156.7 r/min, resulting in an Fe3+ reduction efficiency of 99.32%. Comparative experiments confirmed that the TOC removal efficiency of the FS-derived reduction solution was comparable to that of commercial FeSO4 in treating aniline-containing wastewater, achieving 44.11% and 44.36%, respectively. Economic analysis showed that the treatment cost using FS decreased from 0.63 $/kg-FS to 0.32 $/kg-FS. This study provides a feasible pathway for energy conservation and emission reduction in the Fenton process by minimising FS generation and enabling its in-situ resource recovery.

Abstract Zinc ferrite, a by-product of zinc hydrometallurgy, is a typical secondary resource. This paper focuses on investigating the factors influencing the sulfuric acid leaching process of zinc ferrite and analyzes the leaching kinetics. The research indicates that the zinc leaching rates of both pure zinc ferrite and zinc ferrite within zinc calcine exhibit positive correlations with individual influencing factors. Moreover, a strong positive synergistic effect exists between leaching temperature and leaching time. The differential impact of various factors on the two zinc leaching rates lies in the interaction involving sulfuric acid concentration, where sulfuric acid concentration acts as a limiting factor for the zinc leaching rate from zinc calcine. Kinetic studies on zinc leaching revealed that the rate-controlling step for zinc leaching from pure zinc ferrite is the surface chemical reaction, with an apparent activation energy of 54.22 kJ/mol. At leaching temperatures of 55 °C, 85 °C, and 95 °C, the zinc leaching rate from zinc ferrite in zinc calcine showed high conformity with both the diffusion model and the surface chemical reaction model, suggesting that the leaching process may be influenced by both kinetic mechanisms at these temperatures.

ABSTRACT As an organic extractant in kerosene, Acorga OR25 was used to study the selective removal of Cr6+, V5+, and Fe3+ contaminants from the sulfate leach liquid of ilmenite. Purifying titanium-rich fluids and facilitating the manufacturing of high-purity titanium dioxide were the goals of the study. Sulfuric acid concentration, extractant dosage, contact time, organic-to-aqueous phase ratio (O/A), and temperature were among the important extraction parameters that were tuned. The findings showed that extraction efficiency rose as acid concentration rose, peaking at 1 M H2SO4. 10% Acorga OR25 was used to obtain maximum removal efficiency of 99.5% for Cr6+, 98.5% for Fe3+, and 81% for V5+. Equilibrium was attained in a mere 15 minutes. The ideal O/A ratio for economic viability and efficiency was 1:1. The complexation of metal ions with Acorga OR25 was verified by FTIR analysis, and thermodynamic analyses showed that the extraction procedure was exothermic and spontaneous. These results show that Acorga OR25 can effectively purify ilmenite leachates, providing a workable method for producing high-grade TiO2 for industrial uses.

Comprehensive extraction of valuable metals from lepidolite by mechanical activation and low temperature sulfation roasting

Theoretical study on the bases-enhanced formic sulfuric anhydride nucleation: A new insight from the mechanism, dynamics, and atmospheric impact.

Proton and water migration regulation drives high-efficiency sulfuric acid concentration via ladder electrodialysis

ABSTRACT Natural graphite is classified as a strategic critical raw material by the European Union due to its strategic significance. The demand is steadily increasing, but the current purification methods are not environmentally sustainable, highlighting the need for greener alternatives. This study investigates the effects – sulfuric acid (H2SO4) leaching, thermal treatment, and their combination – on natural graphite from a flotation pilot plant. In the sulfuric acid leaching, the influences of reaction time (60–300 min), temperature (70–100°C), sulfuric acid concentration (0.5–3 mol/L), and liquid-to-solid ratio (10–20 mL/g) were systematically studied using experimental design. Leaching effectively removed 91.4% iron and 52.9% aluminum, but was ineffective against silicon-containing phases. A short 15 min thermal treatment at 2400°C in an argon atmosphere using induction annealing eliminated most silicon phases and other impurities, although residual 2.65 mg/g iron and 1.27 mg/g silicon remained. The combined approach reduced iron and silicon contents to 0.24 and 0.25 mg/g, respectively, and increased the carbon content from 78.4 to 97.6 wt% to near commercial battery-grade levels (98.0 wt%). Additionally, the combination-treated graphite exhibited the lowest degree of structural defects, offering a more sustainable route for purifying natural graphite to high-purity levels compared to conventional halogen-containing techniques.

Abstract This study investigates the macroscopic mechanical behavior of steel wire ropes under corrosive conditions, specifically focusing on the effects of sulfuric acid exposure. The goal is to simulate and analyze the degradation process in service by conducting monotonic tensile tests on both undamaged and artificially pre-damaged 19 × 7 circular strand steel wire ropes. These ropes were subjected to varying levels of corrosion in order to evaluate their mechanical properties. To systematically explore the influence of multiple factors on the degradation process, the Taguchi method was applied, utilizing an L9 orthogonal array with three experimental factors: sulfuric acid concentration, immersion time, and the number of strands removed from the wire rope. Each factor was tested at three levels to determine its impact on corrosion resistance. Steel wire ropes were exposed to sulfuric acid concentrations of 20 %, 30 %, and 40 % for immersion times of 1–3 h, with 0, 2, and 4 strands removed. The maximum tensile strength decreased from 516.415 N in the reference sample to between 482.83 N and 35.63 N after corrosion, corresponding to a 6.5–93.1 % reduction. Statistical analyses, including the signal-to-noise ( S / N ) ratio and analysis of variance (ANOVA), were used to identify the optimal parameter settings for maximizing mechanical performance. The results indicate that the number of strands removed has the most significant influence on the rope’s mechanical properties, followed by the concentration of sulfuric acid and the immersion time. A confirmation test was performed to verify the accuracy and consistency of the optimal parameter configuration, ensuring the reliability of the findings. This study highlights the importance of optimizing key parameters to enhance the corrosion resistance of steel wire ropes, thus extending their service life in corrosive environments. The use of the Taguchi method in this context demonstrates its effectiveness in optimizing mechanical properties and provides valuable insights for improving the durability of wire ropes in industrial applications.

The current work delves into the interactive effects of hard anodizing variables, including electrolyte concentration, temperature, current density, and time, on the microstructural, mechanical, and tribological characteristics of 6061 aluminum alloy. The results demonstrate that the final film characteristics are controlled by a kinetic balance between electrochemical oxide formation and chemical dissolution. The influence of electrolyte concentration and temperature was found to be non-monotonic, while a substantial synergistic effect between current density and time was observed. A maximum hardness of 679HV and a thickness of 59μm was achieved using a sulfuric acid concentration of 190g/L, an electrolyte temperature of -2°C, a current density of 4.4A/dm2, and a duration of 60min. These were considered the optimal anodizing conditions. Tribological examination confirmed the enhanced film's tribological behavior, exhibiting noticeably lower mass loss and a more stable coefficient of friction than the bare substrate. This enhancement is attributed to a shift in the wear mechanism from severe adhesive wear on the substrate to milder abrasion and, at high loads (50N), brittle fracture on the hard anodic film.

The efficient recovery of platinum (Pt) from spent catalysts is of critical strategic importance to alleviate resource scarcity and supply chain dependencies. This study developed an ultrasonic-assisted leaching process using a H2SO4-NaCl system for Pt extraction from spent petroleum catalysts. Single-factor experiments were first conducted to identify the preliminary effects of key parameters. Subsequently, Response Surface Methodology (RSM) based on a Box–Behnken design was employed to model and optimize the interactive effects of ultrasonic power, sulfuric acid concentration, leaching time and NaCl concentration. The results demonstrated that ultrasonic power had the most significant influence on Pt leaching efficiency. The optimized conditions were determined as ultrasonic power of 300 W, H2SO4 concentration of 60%, leaching time of 100 min, and NaCl concentration of 0.10 mol/L. Under these optimal parameters, the Pt leaching rate reached approximately 99.8%, validating the model’s high accuracy and reliability. This work provides an efficient and stable technical pathway for the sustainable recycling of platinum from secondary resources.

This study investigates the extraction of uranium (VI) from aqueous solutions using an emulsion liquid membrane (ELM) system. The ELM system consisted of kerosene as the organic diluent, di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the extractant, and sorbitan monooleate (Span-80) as the surfactant. Sulfuric acid and potassium chloride were used as the stripping solution and tracer, respectively. Response Surface Methodology based on Central Composite Design was applied to examine the effects of process variables, including surfactant concentration in the membrane phase, sulfuric acid concentration in the stripping phase, initial pH of the feed phase, and mixing speed, as well as their interactions. Hydrodynamic parameters were optimized to maximize U(VI) extraction while maintaining high membrane stability. The optimization results revealed that the highest extraction efficiency was achieved by adjusting the Span 80 volume percentage to 1.93% (V/V), sulfuric acid concentration to 0.75 mol/l, feed phase pH to 3.03, and mixing speed to 180.56 rpm. The role of feed-phase pH was found to be significant in the ELM process for U(VI) pertraction. Under these conditions, an extraction efficiency of 99.94% was obtained, with optimized values for emulsion breakage, swelling, and stripping being 0.21%, 3.29%, and 99.69%, respectively.

This paper explores the optimization of in-situ uranium leaching efficiency through the application of oxygen as an oxidizing agent in the lixiviant. With this objective in mind, geological characteristics of the target site were examined, followed by a series of laboratory and pilot-scale experiments. The resulting data were systematically processed and analyzed. The influence of sulfuric acid concentration on the degree of oxygen enrichment in the lixiviant was established. Laboratory tests on core samples from the uranium deposit revealed consistent relationships between uranium concentration in the pregnant solution, the oxidation states of iron (Fe2+ and Fe3+) in lixiviant, and the level of oxygen saturation. Comparative results of uranium content in the pregnant solution over time were obtained for both the conventional and oxygen-enriched technologies. Laboratory results demonstrated a 23.0% increase in uranium concentration in the pregnant solution using an oxygen-enriched lixiviant over the control solution, indicating a potential reduction in recovery time and final metal production costs. Pilot-scale tests at a uranium mine confirmed the positive effect of oxygen-enriched lixiviant on iron oxidation and uranium concentration in the pregnant solution. All pumping wells within the test block showed increased or stabilized uranium concentration upon connecting a special injection system for oxidation in injection wells surrounding the pumping wells, and decreased uranium concentration after system disconnection.

Electrolyte-free electrochemical ammonia stripping integrated with flocculation for efficient nitrogen recovery from swine manure biogas slurry.

With the continuous expansion of copper smelting scale, copper concentrate resources are increasingly scarce, leading to the utilization of low-grade and complex copper concentrates. This results in anode passivation during the copper electrolytic refining process due to high impurity contents. To address this issue and to stabilize cell voltage while improving the overall efficiency of electrolytic refining of high-impurity anode copper, the effects of additives, electrolyte free sulfuric acid concentration, and technological operation parameters on cell voltage variation were investigated based on the unique electrolyte feeding mode of parallel flow technology. The results indicate that, to stabilize the cell voltage of high-lead anode copper electrolysis at high current density, the recommended operating conditions include a bone glue dosage of 40–90 g/t, a thiourea dosage of less than 100 g/t, and a free sulfuric acid concentration in the electrolyte of 160–180 g/L.

The present study explores, for the first time, the potential of pomegranate peel as a reductant agent for the reductive leaching of manganese concentrate, where pyrolusite is the primary valuable mineral. Furthermore, the influence of several factors on the reductive leaching process, including agitation speed, sulfuric acid concentration, peel quantity, reaction temperature and time were investigated. Under optimized conditions of 1.5 M sulfuric acid, temperature of 75 °C, agitation speed of 450 rpm, reaction time of 4 h and pomegranate peel quantity of 5 g, the recovery of dissolved manganese reached 96.12%. Scanning electron microscopy of the leaching residue revealed the dissolution of pyrolusite. Fourier-transform infrared spectroscopy analysis was conducted on both the pomegranate peel and the leaching residue to identify changes in functional groups. Additionally, the kinetics of the reductive leaching process were examined, indicating that the reaction rate is controlled by a surface chemical reaction mechanism with an activation energy of 38.39 kJ/mol. The enthalpy and entropy changes of the reaction were determined to be 35.71 kJ/mol and 192.90 J/mol·K, respectively. Based on thermodynamic values, the Gibbs free energy at temperatures of 303, 318, 333 and 348 K was found to be 94.16, 97.05, 99.95 and 102.84 kJ/mol, respectively.

Enhanced vanadium recovery from vanadium-bearing steel slag is essential in the sustainable use of metallurgical solid waste. This study uses microwave-assisted acid leaching on roasted clinker and systematically investigates it to enhance vanadium recovery; uses response surface methodology (RSM) to identify optimal parameters for leaching; and the influences of sulfuric acid concentration, leaching time, liquid-to-solid ratio (L/S ratio), and leaching temperature on vanadium dissolution are evaluated. The optimal leaching parameters are identified as an L/S ratio of 10:1, 41% sulfuric acid concentration, 65 min leaching time, and 92 °C leaching temperature, under which the highest vanadium extraction rate is 84.58%. Kinetic studies revealed that the leaching behavior during the initial 30 min followed a shrinking core model with fixed particle size. The vanadium microwave-assisted acid leaching process exhibited the observed activation energy (Ea) of 37.30 kJ·mol−1, following a kinetic order of 1.5392 relative to sulfuric acid concentration, implying that ion transport across the solid phase formed during the reaction determined the step that limits the reaction rate. The semi-empirical kinetic equation established in this study accurately describes the leaching behavior under different conditions. This research establishes a theoretical framework and technical reference for boosting vanadium recovery from steel slag, which uses microwave-assisted leaching technology.