Metal Leaching Research Articles

Stepwise extraction of zinc, indium and lead from secondary zinc oxide dusts experimental study

Secondary zinc oxide dust is rich in high-grade metals such as Zn, In, Pb, and Ga, and in the face of the depletion of ore resources at home and abroad, it is of great significance to seek an efficient process to realize the full resource recovery of valuable metals in secondary zinc oxide dust. In this study, on the basis of the thermodynamic analysis of the wet treatment process, three wet treatment methods, namely “low acid leaching”, “high acid leaching” and “chlorination leaching”, were used to explore the suitable parameters for stepwise extraction of Zn, In and Pb metals. The results showed that the three wet treatment methods could effectively extract the corresponding main elements, and the optimal leaching rates of Zn, In and Pb were 73, 90 and 94%, respectively. Thermodynamic analysis shows that under ideal conditions, the “cascade separation” of some or all metals can be theoretically achieved by using a suitable leaching solvent for zinc oxide dust. The concentration of sulfuric acid, the ratio of liquid solid volume to mass and temperature had great effects on the leaching rate of Zn and In, and the leaching rate of Zn and In also increased with the increase of the values of the three experimental parameters, which was positively correlated. The leaching rate of Pb will increase with the increase of sulfuric acid concentration, but when the pH of the solution system is < 2, Pb will form PbSO4 precipitate, which inhibits the leaching ability of Pb. In the chlorinated leaching system with “ammonium chloride + hydrochloric acid” as the leaching solvent, the excess Cl− and Pb2+ fully coordinated to promote the efficient leaching of Pb metal, and the initial pH value of the solution had a great influence on the Leaching Rate of Pb. The multi-stage combined wet treatment process is an effective solution to realize the full quantitative recovery of valuable elements in Secondary zinc oxide dust, In this paper, the suitable process conditions for stepwise extraction of Zn, In and Pb metals were obtained through wet treatment experiments, and the cascade separation of metals in zinc oxide dust was preliminarily realized, which provided an important idea for the efficient utilization of metallurgical dust and sludge solid wastes, and at the same time provided theoretical support for the industrial practice of recycling valuable elements in metallurgical dust.

Metals leached from aluminium foil into Clarias gariepinus muscles roasted at high temperatures: Potential contamination and controlling factors

Aluminium (Al) foil can leach metals into fish during roasting, potentially creating health implications, which informed this study. The roasted (using Al foil) and unroasted fish (control) samples (n = 48) were analysed for metals (Al, Co, Pb, Ni, Cr, Cd, and As) using ICP-AES. The following ranges were recorded for Al (5.51 - 6.35 mg/kg), Co (0.25 - 0.35 mg/kg), Pb (0.48 - 0.65 mg/kg), Ni (2.37 - 4.70 mg/kg), Cr (0.25 - 0.43 mg/kg), Cd (0.05 - 0.07 mg/kg), As (0.32 - 0.45 mg/kg). According to redundancy analysis, foil area had the most influence on metal leaching. The percentage weight loss of the foil after fish roasting indicates leaching of its metal contents into the fish. The EDI and THQ of As, and HI of metals indicate potential risk over time, as a result, roasting of fish with foil should be discontinued.

A novel acid resource: waste hydrochlorofluorocarbons refrigerants selective leaching Cu-In-Ga-Se (CIGS) and catalyzed mineralization under the hydrothermal atmosphere.

With the upgrading and obsoleting of electric refrigeration equipment, significant amounts of waste hydrochlorofluorocarbon (HCFCs) refrigerants are being generated, bringing serious ozone-depleting and global warming effects. HCFCs, containing chlorine and fluorine, have the potential to be converted into acids by mineralization. Hydrothermal technology possesses a tightly sealed environment and high thermal efficiency, providing significant advantages in treating volatile HCFCs. However, the stable C-F bonds and the by-product CClF=CH2 greatly impede the mineralization of HCFCs. Herein, an indium compound from waste CIGS (CuInxGa1-xSe2) was introduced to promote the process, and this strategy successfully increased the mineralization rates of organic chlorine and fluorine to 99.2% and 95.7%, respectively. The acid produced from HCFCs degradation was utilized for the selective leaching of metals in CIGS. Meanwhile, the leaching product InOOH catalyzed further degradation of HCFCs. We revealed that InOOH can adsorb reactants and provide interfaces, resulting in (i) the elongation of C-X (F, Cl) bonds; (ii) a reduction in the energy barrier of the CClF=CH2 degradation reaction. This study provides a promising approach and theoretical basis for the harmless treatment and resourceful utilization of waste refrigerants containing Cl and F.

Enhanced elevated-temperature performance of LiMn2O4 cathodes in lithium-ion batteries via a multifunctional electrolyte additive

LiMn2O4 is a promising cathode material for lithium-ion batteries (LIBs) due to its low cost, environmental friendliness, and high voltage operation. However, its electrochemical performance deteriorates at elevated temperatures, primarily by reason of the structural degradation during cycling and proliferation of adverse reactions at the electrode/electrolyte interface. One of the main reasons is that the hydrolysis and decomposition of the LiPF6 at high temperatures produces HF, which leads to corrosion at the electrode/electrolyte interface and accelerates manganese dissolution. In this work, we report a multifunctional silane-based electrolyte additive, trimethoxyphenylsilane (TMPS), to solve these problems. Theoretical calculations and experimental results both demonstrate that TMPS can eliminate HF, stabilize PF5, and inhibit LiPF6 hydrolysis, thereby mitigating transition metal leaching. Additionally, TMPS improves the stability between cathode and electrolyte by constructing a highly stable and homogeneous cathode-electrolyte interfacial. The LiMn2O4//Li cell using the electrolyte containing 1 wt% TMPS retains 95.5 % and 83.7 % of its capacity after 500 cycles at 25 °C and 60 °C, respectively. Moreover, 18650-type cylindrical cells with this electrolyte also exhibit enhanced electrochemical performance at elevated temperatures. It demonstrates that TMPS is a promising multifunctional additive for manganese-based cathodes in LIBs.

Enhanced heavy metal immobilization in cementitious materials through CO2 mineralization: A kinetic analysis and physicochemical evolution

The leaching of heavy metals (HMs) from industrial solid waste during its treatment and utilization has garnered extensive attention within the scientific community. The incorporation of cementitious materials to both consume waste and immobilize HMs within the construction sector is a promising strategy. Traditional suppression techniques, employing additives, incur higher costs and may adversely affect the mechanical performance of cement. This research introduces a CO2 mineralization technology synergistically enhancing the immobilization of HMs, which inhibiting the leaching channels in cement-based materials and strengthening the chemical chelation of HMs, thereby suppressing their leaching. The results indicated that the cementitious materials, with a carbonation rate of 10 %-12 %, demonstrated enhanced physical adsorption and chemical chelation capabilities, achieving a 98 % reduction in Pb leaching and a decrease of over 50 % for Mn. Conversely, the post-mineralization reduction in free Ca2+ ions adversely affected the immobilization of soluble HMs like Cr(VI). Overall, this study aimed to enhance the efficacy of current methods for utilizing solid waste and sequestrating HMs whilst simultaneously pioneering innovative concepts for the mineralization application of cement-based materials.

Long-term soil remediation using layered double hydroxides: Field evidence for simultaneous immobilization of both cations and oxyanions

Layered double hydroxides (LDHs) have great potential for immobilizing potentially toxic elements in soil. Nevertheless, their practical effectiveness under field conditions remains largely unknown. In this study, we conducted a 2.5-year field trial using pristine Mg-Al LDHs, Ca-Al LDHs, and iron (Fe)-modified LDHs to simultaneously immobilize both oxyanions (including As and Sb) and cations (including Cd and Pb) in historically contaminated soil affected by mining activities since the 1950s. The immobilization performance of LDHs was examined using various batch tests, including water and DTPA extraction, and by measuring metal(loid) concentrations in Coriandrum sativum (coriander). We found that both pristine and Fe-modified LDHs showed promising initial immobilization performance 7 days after application, achieving significant reductions in DTPA-extractable concentrations of As, Sb, Cd, and Pb by 45.6%–68.3%, 55.4%–94.2%, 11.2%–50.9%, and 62.9%–64.9%, respectively, compared to the control soil without amendment. Notably, pristine LDHs showed diminished immobilization performance in the long term, while Fe-modified LDHs exhibited long-term stability over 2.5 years. A conditional probability-based model was used to depict long-term metal(loid) leaching characteristics in LDH-amended soils. Temporal changes in metal(loid) concentrations in the aboveground edible parts (namely, stems and leaves) of coriander corroborated well with DTPA extraction results. Coriander grown in Fe-modified LDH-amended soils had much lower metal(loid) concentrations compared to those grown in pristine LDH-amended soils. As a result, reductions of 35.1%–42.2% for As, 54.4%–66.2% for Sb, 8.5%–22.8% for Cd, and 56.0%–62.7% for Pb concentrations in coriander were still observed 2.5 years after soil amendment with Fe-modified LDHs. To the best of our knowledge, this is the first field-based evidence using LDHs to simultaneously stabilize both cations and oxyanions in soil. The findings support the potential of LDHs for long-term immobilization of metal(loid)s in soil.

Liquid Metal Leaching for Rare Earth Magnet Recycling

This study investigates the optimization of liquid metal leaching for recycling rare earth elements (REEs) from NdFeB magnets, a critical step in addressing the increasing demand for these materials in various high-tech applications. We explored the effects of leaching time, stirring, and magnet demagnetization on the yield of the leaching process using molten magnesium. Conducted at 900 °C, our experiments assessed the leaching process over periods of 2, 3.5, and 5 h, with and without the application of stirring. Our findings show that longer leaching times considerably increase neodymium (Nd) and praseodymium (Pr) leaching yield, with a notable peak in efficiency found at 5 h. Stirring improved the uniformity of REEs significantly and resulted in up to 80% yield. Furthermore, our data show that pre-leaching magnet demagnetization improves leaching specificity, significantly reducing the presence of non-target metals like nickel and copper. These insights offer a pathway to more cost-effective recycling of REEs from magnet scrap, which is essential for environmentally conscious management of resources amid the escalating global demand for REEs.

Efficient degradation of ciprofloxacin by peroxymonosulfate activated with Co-loaded waste biomass: Efficiency, stability, and mechanism

Waste-derived biochar (BC) loaded with transition metals holds promising potential for remediation of wastewater, owing to the high efficiency and minimal risk of metal leaching. Herein, gold passion fruit shell (PFS) derived biochar loaded with cobalt (Co-PFSBC) was synthesized for removal of ciprofloxacin (CIP) from water by activating peroxymonosulfate (PMS). Both the pyrolysis temperature and the Co doping load significantly influence the physicochemical property of Co-PFSBC, thereby affecting the removal efficiency of CIP. 98.51 % of CIP (10 mg/L) is removed within 120 min under the optimal conditions with 100 mg/L of 4 %Co-PFSBC-400 and 1.5 mM of PMS. In addition, 4 %Co-PFSBC-400 shows excellent catalytic performance for a wide range of refractory organics. Based on the quenching experiment and electron paramagnetic resonance (EPR), both radical and non-radical process (singlet oxygen, 1O2) are involved in the 4 %Co-PFSBC-400/PMS system. The total concentration (2.44 mM) of 1O2 generated in the first 30 min reaction indicates that 1O2 plays a major contribution in the CIP degradation. Moreover, the toxicity of CIP and its degradation intermediates were calculated and a plausible mineralization pathway is proposed according to the intermediates.

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.

Target immobilized phases of heavy metals in hazardous waste based lightweight aggregate

The potential leaching risk poses a concern for the large-scale recycling of hazardous waste as lightweight aggregates (LWAs). This paper investigated the combination state of heavy metals in target immobilized phases of LWA through both theoretical calculations and experimental verification. Results reveal that Pb can enter the feldspar crystal cell to form stable interstitial solid solutions, while Cu, Cr, and Ni can replace specific ions in spinel to form replacement solid solutions. The addition of target immobilized phases generally weakened the physical performance of LWAs, while reducing the leaching risk. The appropriate amount of the spinel phase favored the immobilization of Cu, Cr, and Ni, whereas albite contributed to the immobilization of Pb with low leaching values. Due to the lower melting temperature, albite could facilitate the introduction of a high-temperature liquid phase, enhancing the migration of Pb²⁺ for better immobilization in glassy phase. In contrast, anorthite exhibited a higher viscosity at 1100 °C, leading to ineffective physical encapsulation of heavy metal ions by the liquid phase. Heavy metal ions react with additional spinel phase at high temperatures to form stable solid solution phases. This study provides a novel method for regulating heavy metal leaching in hazardous waste-based LWA.

Zero Valent Iron/Ni (FeNi) bimetallic heterostructure for scalable fabrication of polyvinylidene fluoride/FeNi films and efficient organic contaminant removal under UV/persulfate system

Surface heterogeneity on nano zero-valent iron (nZVI) with an additional metal is expected to enhance the catalytic performance and stability by inhibiting metal corrosion and leaching. The influence of passivation by Ni/NiO on the stability of nZVI is examined through degradation performance of uniformly aged nZVI and nZVI/Ni (FeNi) samples via photo-Fenton like reactions under UV/potassium persulfate (PS) system. FeNi bimetallic nanoparticles (BNPs) exhibits enhanced degradation than bare nZVI as thin layers of Fe3O4 and NiO which contribute towards photocatalytic degradation and anticorrosive effects by nickel inclusion. FeNi BNPs achieve 98 % degradation for pharmaceutical antibiotic levofloxacin (LEVO) within 120 min and 93 % degradation for Methylene Blue dye (MB) within 60 min, outperforming nZVI. To overcome secondary pollution, a stable polyvinylidene fluoride (PVDF)/FeNi film was fabricated to treat the contaminated water. The free-floating PVDF/FeNi film achieved 95 % degradation of MB and 98.3 % degradation of LEVO, maintaining a degradation efficiency of 95.9 % after five successive cycles. FeNi BNPs are also immobilized in the dialysis membrane resulting in 99.9 % and 99 % removal of MB and LEVO respectively. MB degradation using PVDF/FeNi film is validated through the micro reactor model developed in COMSOL Multiphysics. The parameters determined from the Langmuir-Hinshelwood (L-H) kinetic model include an intrinsic rate constant of 2.18 ×10−6 mol m−3 min−1 and an adsorption constant of 1.43 ×1019 m3 mol−1. This work introduces a cost-effective and scalable technique for the efficient remediation of contaminants in wastewater.

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.

Leaching Kinetics of Valuable Metals from Calcined Material of Spent Lithium-Ion Batteries.

This study aimed to investigate the leaching kinetics of valuable metals contained in the calcined black mass derived from the incineration of spent lithium-ion battery (LIB) modules. The effects of sulfuric acid (H2SO4) concentration (0.5-3 M), hydrogen peroxide (H2O2) concentration (0.5-2.0 vol %), solid/liquid (S/L) ratio (25-75 g/L), leaching time (10-120 min), and leaching temperature (30 °C-70 °C) on metal leaching efficiency from black mass were investigated. The optimal leaching conditions were achieved with 1 M H2SO4, 1 vol % H2O2, and a S/L ratio of 50 g/L at 60 °C for 60 min. Under these conditions, Li, Ni, and Mn had leaching efficiencies of 100%, with Co at 97.17%, respectively. An investigation of the leaching kinetics utilizing H2O2 as an additive revealed that the Avrami model fits the metal leaching process. The results of this study suggested that diffusion and surface chemical reactions controlled the leaching mechanisms of these metals, with activation energies of 7.829, 5.646, and 5.077 kJ mol-1 for Li, Ni, and Co, respectively.

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.

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.

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

Hydrometallurgy 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.

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.