Metal Leaching Research Articles

The Toxicity Leaching and the Cement Admixtures Properties with Incineration Fly Ash of Different Furnace Types.

Incineration of fly ash is a hazardous solid waste, and there are two types of furnaces used for production. The impact of furnace types on the properties and toxicity of incineration fly ash was studied. The resource utilization of incineration fly ash has been tested. The results showed that circulated fluidized bed (CFB) ash and grate (GF) ash were alkaline materials, dioxin content ranged between 98 and 359 ng-TEQ/kg, and heavy metals exceeded 7700 ppm. The leaching of Zn in CFB ash was 110.474 ppm, and that in the GF ash was 5.985 ppm. The chlorine content in GF ash was 27.07%, 2.7 times that of CFB ash. When the content was 5%, GF ash promoted cement grinding and improved the 3-day compressive strength of cement, which was 35.55% higher than the control sample. CFB ash generates hydrogen gas during the hydration process, causing volume cracking. When 20% GF ash was added, the hydration heat release peak appeared 10.5 h ahead of time. According to the Chinese standard GB 175-2023, the maximum dosages of CFB ash and GF ash in cement were 0.22 and 0.57%. There was no risk of excessive leaching of heavy metals. During cement production with CFB and GF ash, attention should be paid to the issues of chlorine and dioxins.

High-Value Resource Utilization of Steel Waste to Prepare Uniform Micronano LiFePO4/C Cathode Material.

Steel slag is a promising secondary resource necessitating recycling and high-value utilization. This study innovatively converted steel slag into micronano FePO4 and well-performing LiFePO4/C through a selective two-step leaching process followed by fast coprecipitation in HMCRR under superior mass transfer, and a subsequent in situ carbothermal reduction afterward, thereby realizing a waste-to-resource conversion pathway. Besides, a metal leaching mechanism was proposed based on comprehensive slag composition analysis, affirming the process selectivity. Thermomechanical analysis for precipitation underscored the importance of controlling reaction pH to prevent the formation of impure sediments. Leveraging efficient leaching and superior mass transfer during precursor preparation, the further-made carbon-coated LiFePO4/C derived from steel slag exhibited favorable morphology and enhanced discharge capacity, especially at high rates, owing to fast ion diffusion kinetics, minimized Li+ migration distance, and improved structure stability. Notably, the discharge capacity could reach 167.44, 153.56, and 119.62 mAh/g at 0.1, 1, and 10 C, respectively.

Chemical Analysis and Flavour Distribution of Electronic Cigarettes in Australian Schools.

Adolescent usage of electronic cigarettes has increased globally. Inconsistent, or absent, labelling of nicotine and other ingredients requires chemical analysis to accurately determine the chemical composition of these products. Electronic cigarettes confiscated from public and private high school students (N=598) were provided for analysis from three regions in New South Wales, Australia. The products were examined for brand, model and flavour and a subset were further analysed for chemical composition (n=410) quantifying nicotine, synthetic cooling agents, flavouring chemicals and prohibited ingredients by gas chromatography-mass spectrometry (GC-MS). The majority of samples provided were fruity-flavoured disposable e-cigarettes across three main brands (IGET, HQD and Gunnpod). Nicotine was quantified in 97.3% of disposable samples with an average concentration of 40.0mg/mL while one refill e-liquid was found to contain nicotine at a low concentration. Almost all samples contained the coolant WS-23 in relatively high concentrations compared to other flavouring chemicals present. Chemicals prohibited under the TGO110 (Australian e-cigarette product standard) were identified in 3.4% of the samples which were chemically analysed. This included the presence of ethylene glycol in moderately high concentrations (up to 13.2mg/mL). Australian students' preferences for fruity, disposable e-cigarettes were identified regardless of region with the vast majority containing high concentrations of nicotine. WS-23 was found in most disposable e-cigarettes, potentially to reduce the throat irritation from nicotine and other flavouring chemicals. The inhalational safety of the samples is of concern due to health risks associated with detected prohibited compounds, particularly ethylene glycol. This is the first study to quantify nicotine, coolants and flavouring chemicals in ecigarette products seized from Australian high school students and has significant implications for future policy development. Students appear to be almost exclusively using disposable ecigarettes with high nicotine concentrations and predominately fruity flavours. WS-23 may potentially be added to disposable e-cigarettes to facilitate the uptake of these products by adolescents unaccustomed to the throat irritation from nicotine and intense flavours. The ecigarette coils were found to have degraded over time, potentially affecting the composition of the aerosol and leaching of metals.

The Fischer‐Lactonization‐Driven Mechanism for Ultra‐Efficient Recycling of Spent Lithium‐Ion Batteries

AbstractHydrometallurgy remains a major challenge to simplify its complex separation and precipitation processes for spent lithium‐ion batteries (LIBs). Herein, we propose a Fischer‐lactonization‐driven mechanism for the cascade reaction of leaching and chelation of spent LIBs. Citric acid undergoes a two‐step dissociation of the carboxylic acid (−COOH) and complexes with the leached metal ion, while the residual −COOH is attacked by H protons to form a protonated carboxyl ion (−COO −). Subsequently, the lone pair of electrons in the hydroxyl of the same molecule attack the carbon atom in −COO − to facilitate ester bonding, leading to the formation of a lactonized gel. The leaching rates of Li, Ni, Co and Mn are 99.3, 99.1, 99.5 and 99.2 %, respectively. The regenerated monocrystalline LiNi0.5Co0.2Mn0.3O2 (NCM523) has a uniform particle size distribution and complete lamellar structure, with a capacity retention rate of 70.6 % after 250 cycles at 0.5 C. The mechanism achieves a one‐step chelation reaction, and the energy consumption and carbon emissions are only 26 % and 44 %, respectively, of that of the conventional hydrometallurgical. The strategy achieves a double breakthrough in simplifying the process and improving environmental friendliness, offering a sustainable approach to the re‐utilization of spent LIBs.

Review of Heavy Metal Removal from Soil: Methods and Technologies

Soil health is vital for ecosystem functioning, agriculture, and human well-being, yet heavy metal contamination poses significant risks to environmental and public health. This review examines various methods for removing heavy metals from contaminated soils, focusing on physical, chemical, and biological remediation techniques. Sources of contamination, including industrial activities, mining, and improper waste disposal, are discussed, alongside the environmental and health impacts of heavy metals like lead, cadmium, and mercury. Physical techniques such as soil washing and excavation effectively reduce contamination but generate secondary waste and incur high costs. Chemical methods, including soil stabilization and chemical leaching, immobilize or extract metals but may risk recontamination. Biological approaches like phytoremediation and bioremediation leverage natural processes for eco-friendly remediation, though they often require longer timescales for significant results. Emerging technologies, such as nanotechnology and biochar application, show promise for enhancing remediation efficacy. However, challenges remain, including economic constraints, regulatory inconsistencies, and the need for sustainable, long-term solutions. Future directions include integrating various remediation techniques, developing eco-friendly technologies, and emphasizing long-term monitoring to ensure the effectiveness of remediation efforts. This comprehensive overview aims to inform future research and policy development to address heavy metal contamination sustainably.

Bioleaching of Printed Circuit Board Waste to Obtain Metallic Nanoparticles

In this work, a biological recovery of metals (copper and gold) from computer printed circuit board (PCB) waste was carried out by bioleaching using Aspergillus niger. Three bioleaching methods comprising one or two steps or using spent medium were tested in an incubator shaker at 30 °C and 160 rpm with different PCB waste concentrations (2.5 to 10 g/L). Glucose was used as the carbon source. The best condition evaluated was carried out in a stirred tank reactor. The FTIR spectrum confirmed the presence of oxalic, citric, and gluconic acids. A. niger showed an efficiency of bioleaching of up to 100% and 42.5% for copper and gold, respectively, using the two-step method with 2.5 g/L PCB waste after 14 days of the process. The efficiency of bioleaching in a stirred tank reactor was 83% for copper and 24% for gold. The mean metallic particle size obtained after bioleaching varied according to the PCB waste concentration (2.5–10 g/L) added in the experiments. A transmission electron microscope analysis confirmed the synthesis of metallic nanoparticles with spherical morphology. The results indicated that the PCBs bioleaching process with A. niger can be an environmentally friendly alternative to current mechanical and metallurgical processes for metal leaching.

Impact of Acid Rain on Release Characteristics of Heavy Metals in Low-Sulfur Tailings with Strong Acid Neutralization Capacity: A Case Study from Northern Guangxi, China

Tailing ponds are major sources of heavy metal pollution. Previous studies primarily focused on tailings with high sulfur content, with limited attention to low-sulfur tailings. This study explored the release behavior of Pb, Zn, and Cd from low-sulfur tailings under simulated acid rain conditions, considering factors such as pH, particle size, and weathering degree. Samples were collected from a lead–zinc tailing pond in the karst regions of northern Guangxi, China. Batch leaching experiments indicated that even with high acid neutralization capacity (ANC = 166.57–167.45 kg H2SO4/t), substantial heavy metal leaching occurred under acidic conditions (pH 2–3), with Pb, Zn, and Cd concentrations increasing 4–6 times compared to neutral conditions. Leachate concentrations were slightly higher in coarser particles than in finer ones, while weathering further enhanced metal release, particularly for Cd. These findings suggest that acid neutralization alone may not be sufficient to prevent heavy metal leaching in low-sulfur tailings exposed to acid rain. However, due to the laboratory scale of this study, further validation through field-scale or mesocosm experiments is necessary to confirm the observed trends and assess their implications for environmental risk management in karst regions.

Enhanced inhibition of heavy metal leaching in incineration bottom ash through accelerated carbonation with ammonium carbonate

The increasing generation of incineration bottom residues poses environmental risks due to heavy metal leaching, while carbonation is one of the effective methods to immobilize heavy metals. This study introduces a novel approach to mitigate heavy metal leaching from incineration bottom ash (IBA) by accelerated carbonation with ammonium carbonate solution. The effect of ammonium carbonate concentration on carbonation efficiency and inhibition of heavy metal leaching was systematically investigated. X-ray fluorescence was used to analyze the composition of IBA, and thermogravimetric analysis (TGA) and inductively coupled plasma optical emission spectroscopy/mass spectrometry were used to determine carbonation capacity and heavy metal leaching, respectively. Results showed that maximum carbonation capacity was achieved at 8 wt% ammonium carbonate concentration at a solid/liquid ratio of 1:5 for 1 h, but the increase in carbonation efficiency slowed down when the concentration exceeded 4 wt%. Ammonium carbonate accelerated carbonation effectively inhibited heavy metal leaching, particularly copper, with an 89% inhibition rate at 10 wt% ammonium carbonate, while diminished effects were observed with chromiun. The effect of the ammonium carbonate concentration on heavy metal inhibition became less significant above 4 wt%, revealing a nuanced relationship between carbonation and heavy metal leaching inhibition. TGA and X-ray diffraction analyses confirmed the formation of insoluble CaCO3 during carbonation, elucidating neomineralization processes that immobilize trace heavy metals. In addition, the study explored the impact of carbonation on leachate pH, emphasizing the interplay between pH reduction and heavy metal leaching inhibition.

Selective leaching of rare earths, base metals and precious metals from used smartphones

ABSTRACT Discarded smartphones represent a valuable source of rare earths (REE), base metals and precious metals. This study focussed on the optimisation of three-stage selective leaching conditions for REE, copper and precious metals (Au and Ag), respectively, contained in printed circuit boards (PCBs) found in end-of-life smartphones. The effects of several leaching conditions, such as sulphuric acid and thiourea concentrations, were investigated using a statistical approach based on a design of experiments using Box–Behnken methodology. Optimum leaching efficiencies were achieved when PCB powder was contacted (solid concentration of 100 g/L) with (1) a 0.2 M H2SO4 solution for 30 min at a temperature of 20°C for REEs; (2) a 1 M H2SO4 solution with 67 g H2O2/L for 180 min at 80°C for Cu and (3) a solution of 42 g thiourea/L in 0.1 M H2SO4 and 9 g Fe2(SO4)3/L for 120 min at 20°C for Au and Ag. Using these optimal conditions, a complete leaching procedure included an REE solubilisation step and a base metal leaching step, both repeated twice, and a precious metal leaching step. This procedure solubilised 91% of the REE, 100% of the copper, 98% of the gold and 87% of the silver contained in the PCB powder during their respective leaching stages.

Electrochemical Deterioration of a Gold Thin Film in Bicarbonate Solution: Correlative Optical, Nano-Mechanical, and Chemical Considerations.

The electrochemical dissolution of metals in liquid electrolytes is of great concern for various electrochemical technologies. However, it is also the focus for boosting metal recovery processes, e.g., from electronic wastes, one of which is the extraction of gold (Au) using eco-friendly electrolytes. To shed more light on the possibility and improvement of such metal leaching, this work presents the investigation of electrochemical deterioration of a Au nanofilm coated on a silicon (Si) support─ubiquitous materials in electronic components─in aqueous potassium bicarbonate (KHCO3) electrolyte, a solution widely used in food products. In addition to the time-dependent in situ Raman spectra revealing the reduced reflectivity of Au associated with its molecular degradation, the significant role of the electric double layer (EDL) at the metal/electrolyte interface is also indicated. Analyzing surface adhesion maps and force-distance spectra acquired using atomic force microscopy and spectroscopy (AFM/AFS), metal degradation is related to nanoscale worm-shaped reconstructed surface features that act as local sites of reduced refractive index. Complemented by the non-negligible fraction of K observed on the treated Au surfaces using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), an electrochemical framework of metal degradation is proposed, depicting the electric-field-induced transport of K+ and H+ ions toward the Au surface regardless of bias polarity and implying the formation of ternary gold hydrides. The consideration of faradic current in the EDL circuit also suggests the occurrence of ternary gold oxides. Such determination is reinforced by the attributability of the polar and electrostatic characteristics of the worm-like features to residual negatively charged anionic clusters of the hydrides and the oxides. The analysis process and the new understanding of metal degradation provide a potential route for inspecting other metal/solution systems.

Hydrodeoxygenation of Isoeugenol-Derived Model Compound over Carbon-Supported Pt and Pt-SnS Catalysts for the Production of Sustainable Jet Fuel.

This study focuses on the sustainable production of bio-jet fuel through the catalytic hydrodeoxygenation (HDO) of isoeugenol (IE). Sucrose-based activated carbon supported bimetallic Platinum-Tin metal sulphides (PtO-SnS/AC) catalyst was prepared for HDO process. Physicochemical properties of catalysts with different spraying synthesis methods (in situ and ex situ metal doping) and Pt loading (0.1-1.0 %) were further investigated. The PtO-SnS/AC catalysts were characterised using various techniques such as X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). Both HRTEM and FESEM results show the successful preparation of a spherical nanoparticles doped over activated carbon, and Pt was dispersed on the outer shell of the particles. The catalytic HDO of IE was evaluated in a batch system and showed a high yield and conversion as follows: IE conversion of 100 %, liquid-phase mass balance of 95.92 %, dihydroeugenol (DH) conversion of 99.32 %, propylcyclohexane (PCH) yield of 88.94 % and 2-methoxy-4-propylcyclohexanol (HYD) yield of 76.19 %. Moreover, the PtO-SnS/AC catalyst exhibited high reusability with low metal leaching and high coke resistance for 10 cycles. The catalyst was evaluated in a continuous flow reactor for 100 h at different reaction temperatures, and interestingly, the catalyst showed low deactivation with a high half-time.

A highly-efficient peroxymonosulfate activator using a sewage sludge derived biochar supported cobalt oxide: Mechanism and characteristics

The application of biochar derived from sewage sludge (BS) in Fenton-like reactions for contaminant removal has attracted considerable attention. Herein, a BS-supported Co3O4 (BS-Co3O4) catalyst was synthesized using a simple two-step hydrothermal-calcination process to achieve highly efficient activation of peroxymonosulfate (PMS). The introduction of biochar effectively inhibited the aggregation of Co3O4 and reduced cobalt leaching. Compared to Co3O4, the mesoporous BS-Co3O4 exhibited an 8-fold increase in specific surface area (SSA) to 111.92 m2∙g−1, and a 46 %-66.4 % reduction in crystal plane size. The interaction between biochar and cobalt oxide resulted in several notable enhancements in the BS-Co3O4 composite. Specifically, there was an increase in sp2 carbon content, a 42.69 % rise in capacitance, and a 79.99 % reduction in charge transfer resistance. These improvements contributed to enhanced PMS activation performance. The BS-Co3O4 also contained a higher content of Co(II), sp2 carbon, and oxygen vacancies (OV). Co(II) played a crucial role in the redox reaction, accelerating the formation of SO4•− and 1O2 during the PMS activation process. Additionally, OV acted as electron capture centers, further promoting the generation of 1O2. Evidence from reactive species investigations and electron paramagnetic resonance (EPR) tests indicated that SO4•− and 1O2 were the main reactive radicals for eliminating tetracycline (TC). Based on the identification of TC intermediates, two potential degradation pathways were proposed, and a reduction in intermediate toxicity was observed. Experiments involving interference and repetition demonstrated that the BS-Co3O4 catalyst was stable and reusable. This work provides a solution with low metal leaching, high recycling performance, and safety for antibiotic wastewater treatment.

A Dual Effect Additive Modified Electrolyte Strategy to Improve the Electrochemical Performance of Zinc-Based Prussian Blue Analogs Energy Storage Device.

Prussian blue analogs (PBA) exhibit excellent potential for energy storage due to their unique three-dimensional open framework and abundant redox active sites. However, the dissolution of transition metal ions in water can compromise the structural integrity of PBAs, leading to significant issues such as low cycle life and capacity decay. To address these challenges, we proposed a dual-effect additive-modified electrolyte method to alleviate such issues, introducing sodium ferrocyanide (Na4Fe(CN)6) into aqueous alkaline electrolytes. It could not only capture Zn2+ dissolved on the surface of Na1.86Zn1.46[Fe(CN)6]0.87 (ZnHCF) electrode material during the cycling process but also conduct redox reactions on the electrode surface to provide additional capacitance. Through experiments and molecular simulation calculations, it showed that Na4Fe(CN)6 can restrict the movement of Zn dissolution into the electrolyte on the electrode surface. Based on this, an asymmetric supercapacitor based on ZnHCF//activated carbon was assembled with a modified electrolyte. The assembled supercapacitor displayed a specific capacitance of 1,329.65 mF cm-2, a power density of 2,900 mW cm-2, and an energy density of 388.28 mW h cm-2. This study provides a new idea for the design and construction of stable and efficient PBA energy storage materials by inhibiting the leaching of transition metals in PBA.

Disintegration of commercial single-use plastics from synthetic and biobased origins and effects on plant growth

Many single–use plastic (SUP) options made of synthetic polymers, bio-based materials, and blends of both are available in the market and used in large quantities. The disintegration of eleven commercial SUP, marketed in Mexico as cups and plates, was investigated in an aerobic home compost environment at a laboratory scale over 180 days. An evaluation of chemical changes, surface morphology, and thermal and mechanical properties was conducted to ascertain the original composition of SUP and the progression of disintegration in samples that are challenging to clean from soil contamination. Furthermore, the impact of residual compost on barley (Hordeum vulgare) plant growth and its correlation with the leaching of heavy metals were explored. The bio-based SUP, but not those made of expanded polystyrene foam, showed a correlation between the disintegration degree (measured by weight loss into particles <2 mm) and a decrease in functional groups (observed by FT-IR), mechanical-thermal stability loss, and surface wear over disintegration time. For instance, the highest disintegration at 180 days was approximately 70% for wheat bran and palm leaf plates, followed by wheat plates and cellulose-PLA cups (60%). In addition to the components listed by the manufacturers, the FT-IR and DSC analysis revealed the presence of polyethylene and polypropylene in cellulose cups and sugarcane plates. These components, impede disintegration but contribute to preserving thermal resistance and hydrophobicity during utilization. Compost derived from expanded polystyrene foam SUP, with 90 days of disintegration, was rich in zinc and chromium and significantly decrease in the root length of the barley plant compared to the control. This demonstrates the necessity of considering the impact of the leaching of additives and secondary microplastics into the environment.

A novel approach for immobilizing Ag/ZnO nanorods on a glass substrate: Application in solar light-driven degradation of micropollutants in water

One of the main challenges in applying photocatalysts for water treatment is the complex separation and recycling process. In this study, we developed highly stable, porous zinc oxide nanorods (ZnO NRs) immobilized on glass vials using a solvent exchange process (SEP) and hydrothermal calcination. Key parameters, including oleic acid concentration and hydrothermal growth time, were optimized to maximize the active surface area, significantly enhancing photodegradation performance. Under the best conditions, ZnO NRs-coated vials achieved nearly 100% degradation of sulfamethoxazole (SMX) in 10 h of simulated solar irradiation. Depositing silver nanoparticles on the surface of ZnO NRs (Ag/ZnO NRs) further improved performance, reducing degradation time to 4 h and increasing photocatalyst stability. The Ag/ZnO NRs-coated vials, optimized with an Ag precursor concentration of 0.05 M, also demonstrated high degradation rates (>99%) for eight organic micropollutants at environmentally relevant concentrations over multiple reuse cycles and with minimal metal leaching. This study presents an innovative, tunable method for immobilizing photocatalysts on glass substrates, offering high surface area, excellent photocatalytic activity, and mechanical properties, making it highly suitable for water treatment applications.

Enhanced catalytic performance of ethyl-levulinate to γ-valerolactone: Effect of copper loading on Ni/KIT-5 catalyst

A facile wet impregnation method was employed to prepare a bimetallic Ni–Cu catalyst on a mesoporous KIT-5 support, keeping the nickel loading constant (5 wt%) while varying the copper wt.% (xCu, where x = 8, 10, 12, 14). Several physico-chemical techniques, including X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed reduction of hydrogen (H2-TPR), and X-ray photoelectron spectroscopy (XPS), were utilized for catalyst characterization. An environmentally friendly NiCu bimetallic-supported catalyst system was developed in response to many problems, including metal leaching, sintering, and cost. A mesoporous KIT-5 silica support with a large surface area was used. The hydrogenation of ethyl levulinate to gamma-valerolactone was studied utilizing a high-pressure stirred reactor and a range of reaction temperatures (120–160 °C), hydrogen pressures (10–30 bar), and reaction periods. Various catalysts were used in the investigation. Among all tested catalysts, the 12Cu–5Ni/KIT-5 one shows excellent activity. The best GVL yield is 84% at a conversion of 100% after 8 h of treatment at 150 °C and 25 bar H2 pressure; the promotion is also 76.1%. Optimization of reaction conditions was shown to correlate the physicochemical parameters of the catalyst with its activity.

Preparation of green and durable magnesium oxysulfate cement using sewage sludge ash: Physical properties, microstructure, and leaching behavior

The aim of this study was to explore the application of sewage sludge ash (SSA) as a substitute for light-burnt magnesium oxide (LBM) in the preparation of magnesium oxysulfate cement (MOSC), in order to achieve the harmless treatment of SSA and improve the performance of MOSC. By adjusting the SSA dosage, a series of MOSC samples were prepared, and their setting time, compressive strength, water resistance, and heavy metal leaching rates were then systematically evaluated. Additionally, their crystal phase composition, relative content, and microstructure were characterized using XRD, TGA, FTIR, and SEM in order to elucidate the mechanism by which SSA affects the properties of the MOSC. The results indicate that the addition of SSA prolongs the setting time of MOSC and reduces its compressive strength. However, pozzolanic SiO2 in SSA can hydrate with MgO to form magnesium-silicate-hydrate gel, effectively improving the water resistance of MOSC. In particular, when SSA replaces 30 % of LBM, MOSC not only meets the heavy metal leaching standards for Class IV surface water in China, but also has a compressive strength of up to 67 MPa and a significant improvement in water resistance by 44 %. This study not only opens up new avenues for the harmless treatment of SSA, but also provides scientific basis and practical reference for optimizing the water resistance of MOSC.

Exploring dealkalization and Cr removal from red mud through freeze-thaw and acid washing: an experimental approach

Red mud (RM) is an industrial solid waste produced during the extraction of alumina from bauxite. The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization. This paper proposes a method for dealkalization and chromium (Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM. This study focused on the Bayer RM and investigated the effects of freeze-thaw (FT)-acid washing (AW) for dealkalization and Cr removal. The variables were the eluent concentration and FT cycles. The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal. After five FT cycles with 0.5 mol/L oxalic acid, the dealkalization and Cr removal rates reached 97.5% and 65.38%, respectively, 16.1% and 7.40% higher than those achieved at room temperature. The repeated FT disrupted the structure of the RM particles, leading to an increase in the pore space between the soil particles. This enables complete eluent contact and reaction with Cr and alkali, thereby enhancing the removal rate. The FT-AW process is suitable for practical engineering applications. It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.

Efficient leaching of valuable metals from spent lithium-ion batteries using green deep eutectic solvents: Process optimization, mechanistic analysis, and environmental impact assessment

The accumulation of over 11 million tons of spent lithium-ion batteries (LIBs) by 2030 highlights a critical environmental challenge posed by their large-scale retirement. The efficient recycling valuable metals from spent LIBs can both reduces environmental impact and mitigates the pressing issue of metal resource scarcity. In this context, deep eutectic solvents (DESs) have become a promising option as an eco-friendly solvent, exhibiting great potential for recycling spent LIBs. Therefore, this work proposed an innovative green DES system consisting of choline chloride (ChCl), DL-malic acid (MAL), and glycerol for the efficient leaching of valuable metals from spent LIBs. Comprehensive experiments were conducted to determine the optimum leaching conditions (130 °C, 60 g/L, MChCl:MAL:Glycerol of 1:1:3, 3 h), achieving high leaching efficiencies of 94.6% for Ni, 96.8% for Co, 93.8% for Mn, and 96.4% for Li. Through characterization techniques, kinetics studies, and density functional theory (DFT) calculations, the leaching process was predominantly governed by surface chemical reaction (1-(1-x)1/3 = kt) within the shrinking core model, exhibited activation energies of 49.89 kJ/mol, 47.66 kJ/mol, 50.51 kJ/mol, and 22.24 kJ/mol for Ni, Co, Mn, and Li, respectively. The propensity for DES to leach metal ions followed the order: Li > Co > Ni > Mn, determined by binding energy and energy gaps. Cl− and −COOH within the DES were capable of forming stable complexes with reduced transition metal ions, revealing an efficient coordination leaching mechanism. Additionally, a life cycle assessment (LCA) was conducted on the environmental impacts of the DES leaching process, confirming it as an effective and environmentally friendly method for recycling spent LIBs. This work avoided the employment of corrosive acids and alleviated the generally harsh conditions associated with DESs leaching, providing a viable solution for recovering spent LIBs.

Dissolution of metals in NCM622 cathode through the Dissimilatory process with Na-lactate by Shewanella putrefaciens

Objectives:The objective of this study is to confirm the possibility of reduction and consequent dissolution of Li, Ni, Co, and Mn from NCM622 cathodes in spent Li-ion batteries through the anaerobic respiration with Na-lactate by Shewanella putrefaciens.Methods:The method involves using anaerobic microbial respiration to mimic dissimilatory metal oxide reduction, allowing metals to be leached from NCM622 cathodes (LiNi0.6Co0.2Mn0.2O2) under near-neutral pH conditions (~7.5).Results and Discussion:The results show that approximately 26 wt% of the total Li, Ni, Co, and Mn were successfully leached into the solution within two weeks. This approach differs significantly from conventional acidic leaching processes, offering a more environmentally friendly and sustainable alternative. In addition, we provide quantitative information regarding the dissolution of NCM622 when it is exposed in environmental systems.Conclusion:In conclusion, microbial-based metal leaching presents a novel, sustainable pathway for recovering metals from spent Li-ion batteries, addressing environmental concerns and reducing dependence on traditional energy-intensive recovery methods.