Leaching Rate Of Metals Research Articles

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.

Synergistic effect of rhamnolipid and Bacillus mucilaginosus on detoxification and activation of municipal solid waste incineration fly ash

In recent years, the substantial increase in municipal solid waste incineration fly ash (MSWIFA) production has made its treatment a critical issue. However, the high toxicity of MSWIFA makes its utilization still in the exploratory stage. In this study, the heavy metal leaching rate, particle size distribution and activity index of MSWIFA were tested to investigate the detoxification and activation effects of Bacillus mucilaginosus on MSWIFA by introducing rhamnolipid. The results show that the microbial treatment can greatly increase the leaching rate of heavy metals in MSWIFA and its 28-day and 90-day activity indexes, especially by the synergistic treatment. For the Bacillus mucilaginosus and rhamnolipid treated MSWIFA (BR-MSWIFA), the maximum leaching rates follow the order from high to low of 85.57% Cr, 78% Cu, 76.38% Zn, 62.78% Pb and 37.65% Mn, while having a low mass loss of less than 5%, which is important for its reuse. Moreover, compared with the untreated MSWIFA (U-MSWIFA), the average particle sizes of Bacillus mucilaginosus treated MSWIFA (B-MSWIFA) and BR-MSWIFA decrease from 8.39 μm to 7.80 μm and 4.31 μm, and the 28-day activity indexes increase from 80.19% to 101.59% and 110.61%. The effect mechanism is that rhamnolipid not only can promote the growth, reproduction, and metabolic acid production of Bacillus mucilaginosus, but also disperse the extracellular polymeric substance (EPS) and MSWIFA particles, thus increase their contact area and the bioleaching. This study provided a theoretical foundation for the harmless treatment and resource utilization of solid wastes containing heavy metals.

Self-supporting CoFe2O4 nanoparticles on 2D g-C3N4/2D loofah activated carbon mediated peroxymonosulfate activation for tetracycline degradation

For antibiotic contaminants, biomass have been regarded as one of the most resource of functional carbonaceous materials due to its biocompatibility, biodegradability, and good adsorption/degradation performance. Herein, a self-supporting CoFe2O4 nanoparticles on 2D g-C3N4/2D loofah activated carbon (CoFe2O4/g-C3N4/BC) is successfully synthesized by simple hydrothermal method using loofah as carbon source and melamine as nitrogen source. The obtained CoFe2O4/g-C3N4/BC materials have a stable hierarchical sandwich structure with macroporous and mesoporous and a large surface area (189.52 m2/g), which can be used as an adsorbent/catalyst for the adsorption/degradation of organic pollutants. With these beneficial properties, the CoFe2O4/g-C3N4/BC material mediated peroxymonosulfate activation exhibits superior catalytic activity in the degradation of organic pollutants under ambient conditions. A model pollutant tetracycline (TC) can be rapidly degraded by 94.97 % within 25 min. The degradation efficiency was sustained at 88.21 % even after five operational cycles, with the cobalt metal leaching rate consistently below 50 μg/L. The inhibition experiment indicates that the main active species in the CoFe2O4/g-C3N4/BC + PMS system are SO4•−, HO• and 1O2, and the degradation of TC is achieved by the synergistic effect of free radical and non-radical pathways. This study provides a new perspective on the treatment of antibiotic wastewater via the sulfate radicals based-advanced oxidation processes (SR-AOPs).

Enhanced Fenton-like catalysis via interfacial regulation of g-C3N4 for efficient aromatic organic pollutant degradation

For the efficient degradation of organic pollutants with the goal of reducing the water environment pollution, we employed an alkaline hydrothermal treatment on primeval g-C3N4 to synthesize a hydroxyl-grafted g-C3N4 (CN-0.5) material, from which we engineered a novel Fenton-like catalyst, known as Cu–CN-0.5. The introduction of numerous hydroxyl functional groups allowed the CN-0.5 substrate to stably fix active copper oxide particles through surface complexation, resulting in a low Cu leaching rate during a Cu–CN-0.5 Fenton-like process. A sequence of characterization techniques and theoretical calculations uncovered that interfacial complexation induced charge redistribution on the Cu–CN-0.5 surface. Specifically, some of the π electrons in the tris-s-triazine units were transferred to the copper oxide particles along the newly formed chemical bonds (C(π)-O-Cu), forming a π-deficient area on the tris-s-triazine plane near the complexation site. In a typical Cu–CN-0.5 Fenton-like process, a stable π-π interaction was established due to the favorable positive-negative match of electrostatic potential between the aromatic pollutants and π-deficient areas, leading to a significant improvement in Cu–CN-0.5's adsorption capacity for aromatic pollutants. Furthermore, pollutants also delivered electrons to the Cu–CN-0.5 Fenton-like system via a “through-space” approach, which suppressed the futile oxidation of H2O2 in reducing the high-valent Cu2+ and significantly improved the generation efficiency of •OH with high oxidative capacity. As expected, Cu–CN-0.5 not only exhibited an efficient Fenton degradation for several typical aromatic organic pollutants, but also demonstrated both a low metal leaching rate (0.12 mg/L) and a H2O2 utilization rate exceeding 80%. The distinctive Fenton degradation mechanism substantiated the potential of the as-prepared material for effective wastewater treatment applications.

Reducing the environmental impact of lithium-ion battery recycling through co-processing of NCM and LFP

Due to its potential environmental hazards and the importance of valuable metal supply, the recycling of spent lithium-ion batteries (LIBs) has attracted widespread attention. The hydrometallurgical process for recycling spent lithium-ion batteries faces the problem of excessive acid consumption and the need for different redox additives to improve the leaching rate of major metals which will result in issues such as resource waste and secondary pollution. In this study, using LFP and NCM as raw materials, the inherent oxidation/reduction characteristics between them were utilized to achieve leaching rates of over 99 % for Ni, Mn, Li, and over 95 % for Co, without the addition of any redox additives under near stoichiometric sulfuric acid. The leaching kinetics and reaction mechanism of different metals indicate that LFP rapidly dissolves in the sulfuric acid solution, with the released Fe2+ acting as a reducing agent. The subsequent slower reaction between Fe2+ and NCM becomes the rate-controlling step. Afterwards, the leachate regulated by solution control can be further used to prepare Ni-Co-Mn hydroxide precursors and lithium carbonate after the formation of FePO4. This method effectively reduces chemical consumption, mitigates environmental footprint, and achieves highly economical recovery of metals from spent lithium-ion batteries.

Innovative synthesis of low-carbon cemented backfill materials through synergistic activation of solid wastes: An integrated assessment of economic and environmental impacts

The accumulation of large amounts of steel slag (SS) and oil shale residue (OSR) causes serious pollution due to the lack of effective ways to utilize them. In this study, OSR, SS, and soda residue (SR) were used to synergistically prepare all-solid-waste low-carbon cemented backfill material (ALCCB). No cement and chemical additives were added to this material, and synergistic activation enabled full utilization of the solid wastes. The total solid waste utilization rate was 100 %. The mechanical characteristics of the ALCCB and the heavy metal leaching rates were determined. The unconfined compression strength of the ALCCB after 28 days was 5.97 MPa, while the slump was 205 mm. These results met the performance requirements for a filling material. The leaching rates for the heavy metals after 28 days conformed to the guidelines for Class III groundwater quality. The mechanism underlying synergistic hydration of the solid wastes was analyzed at the micro- and macroscale with X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). The results indicated that hydration of the ALCCB occurred continuously during curing, and the faster early hydration reaction stabilized heavy metal curing at 7 d. In addition, ALCCB offers greater economic and environmental advantages than cementitious materials. Notably, the economic and environmental benefits of ALCCB were found to supersede those of cement-based materials, with a cost reduction of 42.6 % and a CO2 emission reduction of 86.9 %. This innovative low-carbon mine backfill material effectively promotes the utilization of solid waste resources and supports sustainable development.

Electro-controlled membrane coupling heterogeneous electro-Fenton (EM-HEF) in treating acetaminophen: performance, mechanism, DFT calculation, and application

The utilization of hybrid electro-Fenton (EF) processes has gained considerable attention, which can combine the advantages of two or more treatment methods resulting in efficient removal of refractory pollutants from water. Here, an electro-controlled membrane coupling heterogeneous EF (EM-HEF) system was constructed for the degradation of acetaminophen (APAP) in water. In the EM-HEF system, a bifunctional ACF/CC-FeOCl-Cu cathode material was synthesized to enhance the HEF reaction, while a tubular Ti microfiltration membrane was used as both cathode and membrane. Degradation experiments indicated the EM-HEF system exhibited remarkable removal efficiency (97.0 %) towards APAP within 30 min under the conditions of flow rate at 60 mL min−1, initial pH at 7.1, and current density at 3 mA cm−2. Notably, the cathode materials showed low metal leaching rate and high APAP removal rate in the 10 cyclic experiments. The common inorganic anions (Cl−, HCO3−, HPO42−, and NO3−) did not inhibit the removal of APAP significantly, whereas humic acid exhibited a more pronounced inhibitory effect only at concentrations exceeding 10 mg L−1. Quenching experiments and electron spin resonance (ESR) tests confirmed the pivotal role of hydroxyl radicals in the decomposition of APAP. Combining density functional theory (DFT) and LC-MS results, three pathways were proposed. The overall toxicity of intermediates was relieved during EM-HEF degradation of APAP. Furthermore, it also achieved good performance in the treatment of landfill leachate, with increasing BOD5/COD ratio from 0.11 to 0.34. This work provides an efficient strategy for the removal of refractory pollutants in water.

Heterogeneous metallaphotocatalytic Cross-Coupling reactions by a carbon Nitride-Nickel catalyst

The integration of heterogeneous photocatalysts with nickel catalysis is garnering considerable interest for their capacity to enable distinct metal-photoredox processes for organic synthesis. However, the challenge about robustness and recyclability of the photocatalyst persists. Herein, a crystalline carbon nitride (MCN-B) photocatalyst with intentionally introduced defects and a dedicated designed active site has been presented. Results reveal by incorporating the deprotonated cyano-group (N-–CN) sites, this host material could provide stable binding sites for Ni (II) ions through the Hard-Soft Acid-Base (HSAB) effect, thereby facilitating charge transmission between semiconductor and metal centers. Consequently, the integrated carbon nitride nickel (Ni/MCN-B) heterogeneous photocatalyst demonstrates high effectiveness in diverse photocatalytic C-N coupling reactions (21 examples, up to 93% yield) under conditions free from organic ligands and additives, which shows competent performance to the homogeneous catalysts. Moreover, the Ni/MCN-B catalyst demonstrates remarkable recyclability, maintaining its photoredox efficiency after 10 cycles with minimal loss of activity and a diminished metal leaching rate, which signifies a substantial advancement in the field of photocatalytic system design.

Cadmium, zinc, and copper leaching rates determined in large monolith lysimeters

Soil mass balances are used to assess the risk of trace metals that are inadvertently applied with fertilizers into agroecosystems. The accuracy of such balances is limited by leaching rates, as they are difficult to measure. Here, we used monolith lysimeters to precisely determine Cd, Cu, and Zn leaching rates in 2021 and 2022. The large lysimeters (n = 12, 1 m diameter, 1.35 m depth) included one soil type (cambisol, weakly acidic) and distinct cropping systems with three experimental replicates. Stable isotope tracers were applied to determine the direct transfer of these trace metals from the soil surface into the seepage water. The annual leaching rates ranged from 0.04 to 0.30 for Cd, 2.65 to 11.7 for Cu, and 7.27 to 39.0 g (ha a)−1 for Zn. These leaching rates were up to four times higher in the year with several heavy rain periods compared to the dry year. Monthly resolved data revealed that distinct climatic conditions in combination with crop development have a strong impact on trace metal leaching rates. In contrast, fertilization strategy (e.g., conventional vs. organic) had a minor effect on leaching rates. Trace metal leaching rates were up to 10 times smaller than fertilizer inputs and had therefore a minor impact on soil mass balances. This was further confirmed with isotope source tracing that showed that only small fractions of Cd, Cu, and Zn were directly transferred from the soil surface to the leached seepage water within two years (< 0.07 %). A comparison with models that predict Cd leaching rates in the EU suggests that the models overestimate the Cd soil output with seepage water. Hence, monolith lysimeters can help to refine leaching models and thereby also soil mass balances that are used to assess the risk of trace metals inputs with fertilizers.

Superior performance of oxygen vacancy-enriched Cu-Co3O4/urushiol-rGO/peroxymonosulfate for hypophosphite and phosphite removal by enhancing singlet oxygen

The treatment of wastewater containing hypophosphite [P(I)] and phosphite [P(III)] is challenged by limitations of traditional Fenton oxidation such as low efficiency, secondary pollution and high costs. This study introduced a facile solvent-thermal method to synthesize Cu-Co3O4 nanoparticles uniformly loaded on graphene (Cu-Co3O4/U-rGO) through the reduction and coordination effects of urushiol (U). As prepared Cu-Co3O4/U-rGO exhibited excellent activity in activating peroxymonosulfate (PMS) for the oxidation of P(I)/P(III) to phosphate [P(V)] (0.229 min−1), along with high stability and reusability (91.5 % after 6 cycles), low metal leaching rate (Co: 0.2 mg/L, Cu: 0.05 mg/L), insensitivity to common anions in water and a wide pH range (3–11). The activation mechanism involved the synergistic effects from both urushiol and graphene, which promoted redox of Cu+/Cu2+ and Co2+/Co3+ and induced abundant oxygen vacancies for PMS activation to produce singlet oxygen. Furthermore, the Cu-Co3O4/U-rGO/PMS was also excellent in the oxidative removal of organic phosphorus. This study is expected to advance strategies for the treatment of P(I)/P(III)-rich wastewater and provide new insights for the development of low-cost, highly efficient heterogeneous catalysts with abundant oxygen vacancies.

Performance and Heavy Metal Analysis of Graphite Tailings Cured Using Cementitious Materials

The massive accumulation of graphite tailings causes serious environmental pollution, mainly from heavy metal pollution. Therefore, this article introduces a method of using graphite tailings as a high-content main material, cement as a small component of the auxiliary cementitious material, and clay as a substitute for cement. The compressive strength and permeability of graphite tailing–solidified material (GT, GT–Clay) were tested, and the effect of clay partially replacing cement as an auxiliary cementitious agent on GT–Clay performance was compared. In addition, inductively coupled plasma mass spectrometry (ICP) was used to analyze the effect of the graphite tailing placement time on the heavy metal content, as well as the changes in the GT heavy metal leaching concentration and its heavy metal content under outdoor freeze–thaw conditions. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to elucidate the microstructural changes in the GT–Clay. The experimental results show that, as the substitution of clay for cement increased from 0 to 50%, the compressive strength of the 90% GT–Clay gradually decreased, and the permeability also increased. The compressive strength of 95% GT–Clay did not show significant changes, but the permeability increased, and when mixed with quicklime, gypsum, and silica fume, the permeability decreased. The Ni and As in graphite tailings fluctuated significantly with the placement time. The heavy metal leaching concentrations of the 90% GT and 95% GT were below the standard limit, and Cd, As, and Ni in GT were potential sources of pollution. The analysis of the microscopic test results showed that the hydration products of the GT–Clay included ettringite, Ca(OH)2, and calcium silicate hydrates. The hydration product stabilized and filled the gaps between the tailing particles, thereby cementing them together. Not only did it improve the mechanical strength of GT, it also reduced the permeability and heavy metal leaching rate. This study provides a new analytical approach to applying graphite tailings for environmental treatment.

Insight on the degradation of P-chlorophenol based on the Co-g-C3N4/diatomite composite photo-Fenton process

The non-metallic photocatalyst g-C3N4 is characterized by non-toxicity and straightforward preparation. Still, the drawbacks of low specific surface area and fast carrier complexation rate limit its practical application in photocatalysis. In this work, Co-doped g-C3N4 was prepared on the surface of diatomite (DE) through a simple one-step calcination method and used to degrade 4-chlorophenol (4-CP). Photocatalytic experiments showed that Co-g-C3N4/DE removed up to 98.7% of 4-CP. The doping of Co could capture the photogenerated electrons, thereby reducing the recombination of photocarriers and accelerating the oxidation–reduction reaction of Co3+/Co2+ and H2O2, promoting the generation of OH. Introducing DE improved the aggregation of g-C3N4 and expanded its surface area. Moreover, the Co-g-C3N4/DE composite material exhibited a low metal leaching rate and good reusability throughout the experiments. In addition, based on DFT calculations, the ROS attack mechanism of 4-CP degradation was speculated and calculated. The final product of 4-CP was found to pose a more minor environmental threat, according to the T.E.S.T. In short, the prepared Co-g-C3N4/DE composite realized the capture of photogenerated electrons and the acceleration of photocatalytic reactions, which are expected to solve the challenges in wastewater treatment.

Extraction of valuable critical metals from coal gangue by roasting activation-sulfuric acid leaching

ABSTRACT Coal gangue is a bulk industrial solid waste produced in the process of coal mining and washing, with the dual attributes of resourcefulness and hazardousness. It can be used as a reserve resource for valuable critical metals such as aluminum (Al), lithium (Li), gallium (Ga), and rare earth elements (REEs). In this paper, the occurrence modes of Li, Ga, and REEs in coal gangue were studied by sequential chemical extraction method. The extraction of valuable critical metals from the coal gangue was systematically studied by roasting activation-sulfuric acid leaching process, and the activation mechanism was elucidated. The results showed that roasting can destroy the inert kaolinite structure in coal gangue and significantly improve the leaching rate of valuable critical metals. Under the optimum conditions, the leaching rates of Al, Li, Ga, and REEs reached 86.51%, 74.46%, 95.45%, and 77.14%, respectively, and the leaching behaviors of Al, Li, and Ga were highly similar. In addition, the characterization of the leaching residue revealed 83.96% silicon oxide content with a loose and porous surface, which could be used to prepare silicon-based products. This study provides the theoretical basis and technical support for the utilization of valuable metals in coal gangue.

Optimization of Synergistic Leaching of Valuable Metals from Spent Lithium-Ion Batteries by the Sulfuric Acid-Malonic Acid System Using Response Surface Methodology

A new environmentally friendly and economical recycling process for extracting metals from spent lithium-ion batteries (LIBs) using sulfuric acid and malonic acid as leaching agents is proposed. By applying Box-Behnken design (BBD) and response surface methodology (RSM) optimization techniques, the global optimal solution of the maximum leaching rate of metals in spent LIBs is realized. The results show that under the optimal conditions of 0.93 M H2SO4, 0.85 M malonic acid, liquid/solid ratio of 61 g·L–1, the temperature of 70 °C and 5 vol% of 30% H2O2, 99.79% Li, 99.46% Ni, 97.24% Co and 96.88% Mn are recovered within 81 min. The error between the theoretical value and the actual value of the metal leaching rate predicted by the regression model is less than 1.0%. Additionally, the study of leaching kinetics reveals that the leaching process of Li, Ni, Co, and Mn in spent cathode materials was affected by the synergistic effect of interfacial mass transfer and solid product layer diffusion. Economic analysis reveals that evaluation index should be fully considered when formulating recovery processes for different metals. This process can reduce the environmental risks of heavy metal disposal, and allow the reuse of metals recovered from spent LIBs.

Mechanical activation for sulfidic tailings treatment by tailings: Environmental aspects and cement consumption reduction

Sulfidic mine tailings are one of the massive hazardous solid wastes, containing large amounts of toxic heavy metals. Poor management of tailings can lead to the production of acid mine drainage and the heavy metal transfer emissions into the environment. Thus, in this study, mechanical activation was used to reuse a combination of carbonate tailings (TC) and sulfidic tailings (TS) for concrete construction purposes and to effectively immobilize heavy metals. The results showed that after tailings treatment, the heavy metal leaching rate was significantly below the allowed criteria based on the toxicity characteristic leaching procedure (TCLP). The mercury intrusion porosimetry (MIP) test results on the specific surface area and porosity after the activation pointed out increase and reduction, respectively. In the concrete sample containing 20 % cement-replacing activated tailings, the critical pore diameter after 28 curing days was 60 nm, which was less than that of the control sample with a critical pore diameter of 150 nm. According to X-ray diffraction (XRD) and scanning electron microscopy (SEM), ettringite and calcium silicate hydrate gel acted as hosts for heavy metals ions and played an inevitable role in stabilizing metal pollutants. Results revealed that the compressive strength of the sample containing 20 % of the activated tailings after 28 curing days was 31.2 MPa, which was higher than the strength of the control sample (26.99 MPa). Overall, it was concluded that the combined mechanically activated mine tailings can be a viable substitute for cement (up to 40 %) for constructing concrete samples. The utilized combined approach led to diminish adverse effect of sulfide content in concrete samples besides the cement consumption reduction.

A three-stage process of Mn(VII)-Fe(III)/PDS system for enhancing sludge dewaterability: Effective driving of Fe(II)/Fe(III) cycle and adequate assurance of ROS

Sludge dewatering helps to reduce the cost of sewage treatment plants and environmental impact. Hence, we used a type of permanganate (Mn(IV)) activated ferric chloride (Fe(III))/ peroxydisulfate (PDS) system to enhance sludge dewaterability. At optimal dose, the simultaneous addition of Mn(IV), Fe(III) and PDS (MFP treatment) reduced the value of specific resistance to filtration (SRF) from 6.76 × 108 s2/g to 2.01 × 108 s2/g. There is a three-stage process during MFP conditioning: oxidation/flocculation, adsorption/oxidation, and reflocculation. X-ray photoelectron spectroscopy (XPS) and Electron spin resonance (ESR) analyses were employed to investigate the oxidation mechanism. Meanwhile, the analysis of Mn valence was improved by considering metal leaching rates. The cycles of Mn(II)/Mn(III)/Mn(IV) were initiated under the reaction between Mn(VII) and extracellular polymeric substances (EPS)/PDS. This process sustained the cycle of Fe(II)/Fe(III) to promote activation of PDS, which continuously promoted to generate OH•, SO4-•, •O2–, 1O2 and Fe(IV). Additionally, sludge EPS was proven to be the primary electron donor of Fe(II)/Fe(III) cycle, resulting in the increasing of Fe(II) proportion. Notably, the hydrophilicity and water-holding capacity of EPS declined significantly following excellent oxidation, which promoted the conversion of bound water. The effective destruction of hydrogen bonds and protein secondary structures explained the outstanding effects. Meanwhile, XDLVO calculation revealed that sludge coagulation performance enhanced through Fe(III) flocculation, MnO2 adsorption and hydrophobic flocculation. Raw and converted free water would be effectively removed through the more hydrophobic surface of large and tough drain pores formed after the reflocculation process. The efficient drainage of sludge water created strong sludge dewaterability. This study verified the practicality of MFP treatment by exploring the oxidation and coagulation mechanisms to clarify the dewatering mechanism.

Recycling lead from copper plant residue (CPR) using brine leaching – Precipitation - Calcination process

Copper plant residue (CPR) is a hazardous industrial by-product possessing both high toxicity and valuable metal content, necessitating its high value-added utilization. Traditional practices in smelters involve stockpiling and landfilling of CPR, leading to substantial land occupation and water contamination. This study focused on the preparation of PbO and Pb3O4 using the HCl–NaCl leaching–conversion–thermal decomposition process, employing CPR as the primary raw material. The effect of various leaching process conditions on the metal leaching rate was explored. A maximum lead leaching rate of 87.65% was achieved under optimal conditions including leaching temperature, liquid–solid ratio, leaching time, HCl molar concentration, NaCl mass concentration, and particle size. The lead content in the leachate was 15.85 g/L. Experimental data indicated that ash diffusion control served as the rate-limiting step in the HCl–NaCl leaching process. The apparent activation energy was determined to be 18.374 kJ mol−1, with a reaction order of 0.8986 concerning the HCl concentration and an L/S ratio of 0.8124. Additionally, response surface methodology enabled the determination of technological parameters for refining PbCl2 into PbCO3 precursors, yielding a conversion rate exceeding 96.50%. Moreover, the technical indicators of PbO and Pb3O4 obtained through low-temperature thermal decomposition of PbCO3 were investigated. The fabricated PbO and Pb3O4 exhibited purities of 99.65% and 99.26%, respectively, effectively transforming CPR from hazardous waste residue into valuable products. The process ensures the efficient recovery of lead to its maximum extent and promotes residue recycling.

Enhanced degradation of tetracycline hydrochloride by activated peroxymonosulfate through Ni-doped LaFeO3

To achieve efficient degradation of tetracycline hydrochloride (TC), we employed a straightforward hydrothermal method to enhance the physicochemical properties of the initial lanthanum ferrite by substituting different ratios of Ni for Fe. Ni doping significantly reduced the energy band band gap of LFNO-5 from 1.93 eV to 1.76 eV, enhanced the visible light response range and photocurrent response, reduced the impedance, and generated more oxygen vacancies. The photocatalytic activity of the target materials was investigated using tetracycline hydrochloride as a model pollutant under the activation of a minute amount of potassium persulfate (PMS) and visible light. After 60 min of exposure to light, LFNO-5/PMS achieved a 90% degradation of TC (k = 0.03374 min−1), surpassing PMS (k = 0.00710 min−1) by a factor of 4.75 and LFO/PMS (k = 0.01781 min−1) by a factor of 1.89. The redox cycling of FeIII/FeII and NiIII/NiII in LFNO-5 facilitated an effective synergistic photocatalytic process. Vacancies (h+) and sulphate radicals (SO4−) played a crucial role in pollutant degradation within the LFNO/PMS system. Furthermore, the LFNO-5/PMS system exhibited excellent resistance to various inorganic ions and humic acids, while delivering noteworthy performance even in the presence of environmental disturbances. The degradation efficiency of the catalyst did not decrease significantly after several cycles, and the metal leaching rate was low, with good stability and reusability. Furthermore, Ni-doped LFO not only improved the activation efficiency for PMS, but also demonstrated the superiority of the LFNO-5 catalyst as a promising activator for PMS effluent remediation.

Study on the synergistic mechanism of sulfuric acid and ammonium sulfate on the extraction of metals from ferronickel slag by roasting

Due to the complex occurrence state of valuable metals in ferronickel slag, the metal extraction rate of the ammonium sulfate roasting process is insufficient. This study proposes a more cost-effective strategy to extract ferronickel slag valuable metals by mixed roasting with sulfuric acid and ammonium sulfate. The effects of the reagent dosage, roasting temperature and roasting time on the metal extraction rate of (NH4)2SO4 roasting, H2SO4 roasting and (NH4)2SO4 and H2SO4 mixed roasting were compared and analyzed. XRD, SEM and TG-DSC were used to reveal the mechanism of mixed roasting to optimize the metal extraction effect from ferronickel slag. The results showed that mixed roasting with a mass ratio of ammonium sulfate to sulfuric acid of 1:1 could reduce the dosage of ammonium sulfate roasting by 2.5 times, and the leaching rates of valuable metals Mg, Fe, Al and Cr increased by 17.46%, 42.8%, 26.06% and 24.89%, respectively. Likewise, comparing to sulfuric acid roasting, the acid consumption of mixed roasting was reduced by two-thirds, and the metal leaching rate was increased by 10.08%, 12.98%, 18.76% and 45.18%, respectively. The “synergistic” mechanism of sulfuric acid and ammonium sulfate on metal extraction by roasting is as follows: ① Before roasting, sulfuric acid partially destroys the surface structure of ferronickel slag particles, forming more pores and channels, creating conditions for the rapid diffusion of ammonium sulfate and sulfuric acid into the slag particles. ② Sulfuric acid reacts with ammonium sulfate to form NH4HSO4, which is more acidic and can accelerate conversion to soluble metal complexes. ③ The addition of sulfuric acid greatly advances the initial temperature of the reaction between ammonium sulfate and metals, widening the temperature range of sulfation roasting and reducing the difficulty of the reaction between ammonium sulfate and metals in ferronickel slag. ④ The liquid–solid reaction increases the reaction interface, improves the mass and heat transfer efficiency and enhances the degree of metal acidification.

A mechanochemical method for one-step leaching of metals from spent LIBs

A one-step system based on mechanochemical activation and the use of grape skins (GS) was proposed to recover metals from lithium-ion batteries (LIBs) cathode waste. The effects of the ball-milling (BM) speed, BM time, and quantity of added GS on the metal leaching rate were explored. The spent lithium cobalt oxide (LCO) and its leaching residue before and after mechanochemistry were characterized by SEM, BET, PSD, XRD, FT-IR, and XPS analysis. Our study shows that mechanochemistry promotes the leaching efficiency of metals from LIBs battery cathode waste by changing the cathode material properties (that is, reducing the LCO particle size (12.126 μm ∼ 0.0928 μm), increasing the specific surface area (0.123 m2/g ∼ 15.957 m2/g), enhancing the hydrophilicity and surface free energy (57.44 mN/m2 ∼ 66.18 mN/m2), promoting the generation of mesoporous structures, refining grains, disrupting the crystal structure, and increasing the microscopic strain, while deflecting the binding energy of the metal ions). A green, efficient and environmentally friendly process for the harmless and resource-friendly treatment of spent LIBs has been developed in this study.