Search Results (252)

Utilization of ozone micro-nano bubbles during uranium leaching process has attracted attention in recent years because of ozone’s potent oxidizing capacity, high efficiency in mass transfer, and environmental compatibility. This review systematically presents the properties, generation methods and characterization approaches pertaining to ozone micro-nano bubbles (OMNBs) for the application of uranium leaching. In addition, the potentials and challenges of using ozone micro-nano bubbles to enhance uranium resources recovery are summarized. A lack of comprehensive understanding regarding uranium oxidation mechanism by ozone micro-nano bubbles under different pH conditions, along with the gaps in field experiments, has hindered the exploration and development of uranium leaching by OMNBs. In summary, further research endeavors on uranium oxidation mechanism by OMNBs and field trials are needed to facilitate the implementation of uranium leaching by OMNBs. Full article

The depletion of natural resources remains a major global challenge, emphasizing the need to develop sustainable processes that enable both metal recovery and waste recycling. This study investigates the leaching of valuable metals from lead smelting slag using methanesulfonic acid (MSA), a biodegradable and environmentally benign reagent. Batch experiments were performed under different MSA concentrations (0.35–1.4 M) and temperatures (22–80 °C). Metal dissolution increased nearly linearly with acid concentration up to 1 M, with maximum recoveries after 60 min of 85% Zn, 64% Pb, 75% Cu, and 68% Fe. Copper dissolution was governed by the oxidation of Cu₂S, while Fe leaching was affected by pH variations that promoted re-precipitation. Kinetic modeling indicated mixed chemical–diffusion control mechanisms, with activation energies of 22.6 kJ mol⁻¹ for Zn and 31–33 kJ mol⁻¹ for Pb, Cu, and Fe. Beyond efficient metal extraction, the process generated a leach residue with reduced concentrations of base metals and a mineralogical composition dominated by stable calcium-silicate phases, improving its potential suitability for reuse in construction or mining backfill applications. Overall, methanesulfonic acid proved to be an effective and sustainable lixiviant, combining high metal recovery with the generation of recyclable slag, thereby contributing to circular metallurgical practices. Full article

While vanadium-extracted tailings contain valuable components, their utilization is difficult due to their high sodium content. In this work, a new oxygen-pressure calcification and alkaline leaching strategy to achieve barium orthovanadate vanadium precipitation is developed to realize the resourceful recycling and utilization of vanadium-extracted tailings. First, the preparation of barium orthovanadate via calcified alkaline leaching and vanadium precipitation was studied, and the effects of CaO addition, NaOH concentration, leaching temperature, and liquid–solid ratio on the leaching rates of sodium and vanadium were evaluated in single-factor experiments. Under the optimum leaching conditions (CaO addition of 20%, alkali concentration of 150 g·L⁻¹, leaching temperature of 180 °C, and liquid–solid ratio of 10:1), the leaching rates of vanadium and sodium reached 85.25% and 82.36%, respectively. Subsequently, the vanadium-containing leaching solution was subjected to a vanadium precipitation test, and the effects of pH, Ba(OH)₂ addition (expressed as ${\mathrm{n}}_{\mathrm{Ba}}/{\mathrm{n}}_{\mathrm{V}}$), vanadium precipitation temperature, and vanadium precipitation time on the vanadium precipitation rate were investigated. Under the optimum vanadium precipitation conditions (pH 14, ${\mathrm{n}}_{\mathrm{Ba}}/{\mathrm{n}}_{\mathrm{V}}$ = 1.5:1, temperature of 30 °C, reaction time of 60 min), a vanadium precipitation rate of more than 99% was achieved. The precipitated vanadium product of this reaction was confirmed to be Ba₃(VO₄)₂ with a purity of more than 99%. Notably, the wastewater generated during the test process can be mixed with an alkali and returned to the leaching process for reuse, and the dealkalized residue can be used as a raw material for ore reduction in iron smelting processes. Full article

A leachate from alkaline leaching of copper shaft furnace (CSF) dust as a hazardous waste was used in this study for performing a chemical precipitation experiment of lead, zinc, and copper. The precipitation processes for lead, zinc, and copper were theoretically optimized based on a thermodynamic study. To determine suitable operating conditions, metal phase stability, reaction mechanisms, and precipitation order were analyzed using the Hydra/Medusa and HSC Chemistry v.10 software packages. In the first experimental stage, treatment of the alkaline leachate resulted in the formation of insoluble lead sulfate (PbSO₄), while zinc remained dissolved for subsequent recovery. In the second stage, the zinc-bearing solution was treated with Na₂CO₃, producing a mixed zinc precipitate consisting of Zn₅(OH)₆(CO₃)_2(s). This study determined that the optimal conditions for chemically precipitating lead as PbSO₄ from alkaline leachate (pH 13.5) are the use of 1 mol/L H₂SO₄ at pH 3.09 and Eh 0.22 V at 25 °C, while optimal zinc precipitation from this solution (pH 3.02) is achieved with 2 mol/L Na₂CO₃ at pH 9.39 and Eh –0.14 V at 25 °C. A small amount of copper present in the solution co-precipitated and was identified as an impurity in the zinc product. The chemical composition of the resulting precipitates was confirmed by SEM–EDX analysis. Full article

This study explores the bioleaching potential of indium from Liquid Crystal Display (LCD) screens originating from end-of-life mobile phones using Acidithiobacillus spp. The LCD panels were mechanically processed, including dismantling, crushing, and milling, and separated into four size fractions: <1 mm, 1–1.5 mm, 1.5–2 mm and >2 mm. These fractions were leached for a period of four weeks. During the experiment, changes in pH value were monitored, and the concentrations of indium in the solutions were measured by using inductively coupled plasma optical emission spectrometry (ICP-OES). The results showed that the highest indium was detected after 4 weeks of leaching for fraction FG <1 mm (146.47 mg/L). The study confirms that bioleaching is an effective and environmentally friendly method for the recovery of critical raw materials such as indium from electronic waste, offering a promising alternative to conventional chemical and pyrometallurgical techniques. Full article

Understanding how the surface charge environment governs pollutant–catalyst interactions is essential for designing efficient photocatalysts. In this study, ZnO–CeO₂–WO₃ composite materials were synthesized through a simplex-centroid mixture design to evaluate their photocatalytic activity toward the degradation of 4-nitrophenol (4-NPOH) under UV irradiation. The materials were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), nitrogen adsorption–desorption (BET/DFT) and scanning electron microscopy (SEM). Photocatalytic experiments were conducted without pH adjustment to analyze the intrinsic behavior of each oxide and their mixtures. The acid–base equilibrium of 4-NPOH (pK_a = 7.2) allowed evaluating its deprotonation to 4-nitrophenolate (4-NP⁻) and its interaction with the catalyst surface, which depends on the point of zero charge (pH_Pzc) of ZnO, CeO₂, and WO₃. The Zn–W binary system (ZnWO₄ phase) exhibited the highest activity, achieving 81% degradation efficiency and the largest apparent rate constant (k = 5.1 × 10⁻³ min⁻¹). However, a 51% decrease in activity was observed after three reuse cycles, attributed to WO₃ leaching induced by the interaction between 4-NPO⁻ and zinc tungstate hydroxide (Zn[W(OH)₈]). This work establishes a direct correlation between surface charge, pollutant speciation, and photocatalytic performance, providing a mechanistic framework for understanding pH-dependent degradation processes over multicomponent oxide composites. Full article

This study presents a comprehensive investigation of copper extraction from chalcopyrite concentrate using choline chloride–malonic acid (ChCl:Ma) deep eutectic solvent (DES) through an integrated experimental and modeling approach. The work began with determination of the deep eutectic temperature (38 °C) for the ChCl:Ma system, which guided the selection of the optimal 1:1 molar ratio to ensure minimal viscosity and maximum solvent stability. The operating temperature range (50–80 °C) was strategically chosen based on TGA analysis confirming the solvent’s thermal stability below 120 °C, ensuring no solvent degradation during leaching experiments. Response Surface Methodology (RSM) with Central Composite Design (CCD) optimization revealed temperature and leaching time (24–72 h) as statistically significant parameters affecting copper recovery, with a highly predictive quadratic model (R² = 0.99, p < 0.0001). Kinetic analysis using the shrinking core model identified a diffusion-controlled mechanism through a sulfur layer, supported by low activation energies (Cu = 29.09 kJ/mol, Fe = 38.16 kJ/mol). Comprehensive characterization showed preferential chalcopyrite dissolution with direct conversion to elemental sulfur (XRD), formation of metalchlorocomplexes (UV-Vis), and excellent solvent thermal properties (TGA). These findings demonstrate ChCl:Ma DES as an effective medium for chalcopyrite processing, with a systematic methodology providing insights for sustainable non-aqueous metal recovery systems. Full article

In this work, two novel nanoscale zero-valent iron (nZVI) composites (nanoscale zero-valent iron and copper-intercalated montmorillonite (MMT-nFe⁰/Cu⁰) and carbon microsphere-supported sulfurized nanoscale zero-valent iron (CMS@S-nFe⁰)) were used to treat soil contaminated with both Cr(VI) and p-nitrophenol (PNP), and added persulfate (PMS). Experiments found that the pollutant removal effect has a great relationship with the ratio of water to soil, the amount of catalyst, the amount of PMS, and the pH value. When the conditions are adjusted to the best (water–soil = 2:1, catalyst 30 g/kg, PMS 15 g/kg, pH 7–9), both materials fix Cr(VI) well and decompose PNP. The removal rates of Cr(VI) and PNP by the MMT-nFe⁰/Cu⁰ system are 90.4% and 72.6%, respectively, while the CMS@ S-nFe⁰ system is even more severe, reaching 94.8% and 81.3%. Soil column leaching experiments also proved that the fixation effect of Cr can last for a long time and PNP can be effectively decomposed. Through detection methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), we found that Cr(VI) was effectively reduced to Cr(III) by Fe⁰ and Fe²⁺ ions and subsequently transformed into stable FeCr₂O₄ spinel oxides, and the groups produced after the decomposition of PNP could also help fix the metal. This work provides a way to simultaneously treat Cr(VI) and PNP pollution, and also allows the use of multifunctional nZVI composites in complex soil environments. Full article

Preferential flow, which primarily drains via vertical and interconnected macropores under gravity, allows water and solutes to transport non-uniformly through the soil matrix. Such a feature exacerbates the leaching risk of pollutants to groundwater. However, there is still a lack of knowledge of how the soil macropores affect the migration of manure-sourced veterinary antibiotics (VAs) in agricultural soils. This study used a series of techniques, including field dye tracing experiments, measurements of soil water retention curves (SWRCs), and micro-CT scanning, to explore macropore characteristics for a typical Entisol. The leaching behavior of sulfadiazine (SDZ) and sulfamethazine (SMZ) was then investigated using undisturbed columns (15 cm ID × 20 cm) under simulated rainfall. The results revealed the great lateral diffusion ability of the soil (up to 65 cm) as compared to vertical penetration (50 cm depth) in the field. The soil was abundant in macropores with equivalent diameter > 200 µm, and the macroporosity was higher in the lower layer (40–60 cm) than the upper layers, where cultivation may lead to the fragmentation of the soil structure and the formation of more isolated pores. Breakthrough curves (BTCs) and hydrological modeling indicated a faster penetration time and greater leaching of sulfonamides with increased macropores in the soil. Such an effect was, however, strengthened under rainstorm conditions (25 mm h⁻¹). Antibiotics leaching was strongly correlated with the mean macropore diameter (MD), compactness (CP), and connectivity (Γ) parameters and significantly affected by MD and CP (p < 0.05), particularly at a moderate rainfall intensity (11 mm h⁻¹). This study has linked antibiotics migration with the soil structure and highlighted macropores’ contribution to their accelerated leaching, thus providing evidence for environmental risk assessments and promoting sustainable soil and water management in real scenarios of soil macropore flow. Full article

CoFe₂O₄ loaded onto red brick powder (CoFe₂O₄@RBP) was synthesized via coprecipitation followed by post-calcination and employed as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for the degradation of methylene blue (MB), thereby valorizing red brick demolition waste within a circular economy pathway and aligning the study with sustainability-oriented resource recovery. The effects of pH, PMS concentration, catalyst dosage, and coexisting substances on MB removal were systematically investigated. Complete MB removal was achieved within 30 min, and the apparent rate constant for the CoFe₂O₄@RBP/PMS system was 0.22 min⁻¹—slightly lower than that of CoFe₂O₄/PMS—while Co leaching was markedly reduced. The process performed well across a broad pH range (3.0–9.0). EPR and radical-quenching experiments indicate that SO₄•⁻ and HO• play a minor role, whereas the Co(II)–PMS complex is primarily responsible for MB degradation; accordingly, common coexisting species (SO₄²⁻, Cl⁻, NO₃⁻, humic acid) exert negligible effects. The catalyst also maintained strong durability across numerous repetitions. These results highlight a cost-efficient route to PMS activation by coupling CoFe₂O₄ with construction waste-derived supports. Full article

The concentrations of natural radioactive elements in the groundwater environment are regulated by several factors, including aquifer geology, groundwater hydrochemical properties, and changes in environmental conditions. Many studies have explored these factors, but few have systematically elucidated the mechanisms underlying the dissolution of radioactive elements from their host minerals into groundwater. This study investigated the petrological, mineralogical, and weathering properties of aquifer materials and their effects on the leaching of uranium (U) and thorium (Th) into groundwater. The time required for the U concentration to reach the drinking water standard (30 μg/L) was estimated through artificial weathering experiments performed under diverse environmental conditions. Rock core samples were obtained from three sites differing in their geology and groundwater U concentrations. Mineralogical analyses revealed that thorite, a representative radioactive mineral that contains large amounts of U and Th, was present in samples from all collection sites. Thorite minerals differed in terms of their sizes, shapes, cracks, and chemical compositions between samples from different sites, indicating that geological features, mineral alteration characteristics, and environmental conditions controlled the behavior of U and Th. These factors appear to play crucial roles in regulating the mobility and potential long-term leachability of U and Th. Artificial weathering experiments confirmed that a neutral pH with surplus bicarbonate ions favored U leaching. Under these environmental conditions, aquifer U concentrations were estimated to require 8.7–226 years to reach the drinking water standard, depending on the groundwater dissolved oxygen content. Our results provide scientific evidence that may be used for managing radioactive elements in the groundwater environment, and are likely to inform new environmental policies and regulatory standards. Full article

Nutrient losses through leaching and low nutrient use efficiency are major challenges limiting crop productivity and causing environmental pollution. Biochar has been widely studied as a soil amendment to improve nutrient retention; however, the combined effects of pyrolysis temperature and post-production oxidation on soil nutrient dynamics and plant performance remain unclear. In this study, wheat straw and wood residue biochars were produced at two pyrolysis temperatures (350 and 450 °C) and subsequently modified by hydrogen peroxide (H₂O₂) oxidation to enhance surface functionality. A pot experiment with fava bean (Vicia faba L.) was conducted to evaluate the effects of pristine and oxidized biochars on soil chemical properties, nutrient leaching, and plant nutrient uptake. Results showed that pristine biochars increased soil pH from 6.82 (control) to 8.73–9.12 and EC from 2.15 to 3.06–4.71 dS m⁻¹, with wheat straw biochars having stronger alkalizing effects. In contrast, oxidized biochars decreased soil pH to 5.62–5.93 due to the introduction of oxygen-containing functional groups. All biochars reduced NO₃⁻-N, NH₄⁺-N, and PO₄³⁻-P leaching, with the most pronounced reductions observed in oxidized wheat straw biochar produced at 450 °C (O-BWS₄₅₀). Improved nutrient retention translated into higher plant nutrient uptake: fava bean plants grown in O-BWS₄₅₀-amended soil achieved the greatest N (6.71%) and P (3.89%) uptake, significantly higher than the control. These findings highlight the potential of oxidation-modified biochars, particularly wheat straw biochar produced at moderate pyrolysis temperature, to improve soil nutrient conservation and enhance crop nutrition simultaneously. Such modifications represent a promising approach for developing biochar-based soil amendments that promote sustainable nutrient management. Full article

Lead (Pb(II)) contamination in water poses severe environmental and health risks due to its toxicity and persistence. This study compares almond shell-derived biochars produced by slow pyrolysis (SP) and microwave pyrolysis (MW), with and without KOH activation, focusing on structural properties and Pb(II) adsorption performance. Biochars were characterized by proximate and elemental analysis, BET surface area, FTIR spectroscopy, and adsorption experiments including pH dependence, kinetics, and equilibrium isotherms. Non-activated SP exhibited the highest surface area (S_BET = 693 m²·g⁻¹), pronounced mesoporosity (≈73% of total pore volume), and the largest observed equilibrium capacities. KOH activation increased surface hydroxyl content but degraded textural properties; in MW samples, it induced severe pore collapse. Given the very fast uptake, kinetic modeling was treated cautiously: for non-activated biochars, Elovich adequately captured the time-course trend, whereas activated samples returned non-physical kinetic constants (e.g., negative k₂) likely due to high post-adsorption pH (>11) and probable Pb(OH)₂ precipitation. Equilibrium data (fitted over 50–500 mg·L⁻¹) were better captured by the Freundlich and Redlich–Peterson models, indicating a mixed adsorption behaviour with contributions from heterogeneous site distribution and site-specific interactions. Optimal Pb(II) removal occurred at pH 4, with no measurable leaching from the biochar matrix. Overall, non-activated SP biochar is the most effective, sustainable and low-cost option among the tested materials for Pb(II) removal from water, avoiding aggressive chemical activation while maximizing adsorption performance. Full article

This paper investigated the tunnel slags generated from a specific tunnel project to systematically assess their environmental risk through phase composition, chemical composition, acidification potential, and heavy metal speciation. Leaching experiments were conducted under various influencing factors, including particle size, time, liquid-to-solid ratio, pH, temperature. The release concentration of heavy metals from the tunnel slag particles follows the following order: Zn > Cu > Cr. This is primarily attributed to the preferential release of Zn under acidic conditions due to its high acid-soluble state, while Cr, which is predominantly present in the residual state, exhibits very low mobility. Furthermore, decreased particle sizes, increased liquid-to-solid ratios, elevated leaching temperatures, extended leaching times, and lower pH values can effectively promote the dissolution of heavy metals from the tunnel slag. The cumulative leaching curves of Cr, Cu, and Zn from the three types of tunnel slags conform to the Elovich equation (R² > 0.88), indicating that the release process of heavy metals is primarily controlled by diffusion mechanisms. The S- and Fe/Mg-rich characteristics of D3 confers a high acidification risk, accompanied by a rapid and persistent heavy metal release rate. In contrast, D2, which is influenced by the neutralizing effect of carbonate dissolution, releases heavy metals at a steady rate, while D1, which is dominated by inert minerals like quartz and muscovite, exhibits the slowest release rate. It is recommended that waste management engineering prioritize controlling S- and Fe/Mg-rich tunnel slags (D3) and mitigating risks of elements like Zn and Cu under acidic conditions. This study provides a scientific basis and technical support for the environmentally safe disposal and resource utilization of tunnel slag. Full article

The growing demand for lithium-ion batteries (LIBs) requires efficient and sustainable recycling solutions. This study investigates bioleaching as an alternative to conventional hydrometallurgical methods, focusing on (i) organic acid-mediated leaching with Gluconobacter oxydans and (ii) sulfuric acid bioleaching with Acidithiobacillus thiooxidans. Experiments were conducted at 26 °C with leaching durations of one to three weeks, depending on the microbial system, at pH 1.35 for sulfuric acid treatments, and with liquid-to-solid ratios equivalent to 100 mL g⁻¹ (A. thiooxidans) or 100 mL g⁻¹ in culture medium (G. oxydans). Results show that indirect bioleaching with G. oxydans achieved high recovery rates for cobalt (96%), manganese (100%), nickel (65%), and lithium (68%), while the direct approach was less effective due to microbial inhibition by black mass components. Similarly, biologically produced sulfuric acid exhibited moderate leaching efficiencies, but chemically synthesized sulfuric acid outperformed it, particularly for nickel (93%) and lithium (76%) after one week of leaching. These findings suggest that bioleaching is a promising, eco-friendly alternative for LIB recycling but requires further process optimization to improve metal recovery and industrial scalability. Future research should explore hybrid approaches combining bioleaching with conventional leaching techniques. Full article