Optimum Leaching Research Articles

Chemical leaching of typical heavy metals from desulfurization sludge in a coal-fired power plant

The issue of excessive heavy metal content in desulphurized sludge from coal-fired power plants is addressed by conducting a study on samples collected from four coal-fired power plants in northern China. In this study, we focus on analyzing the physicochemical properties of the sludge and the concentrations of heavy metals such as Cr, Ni, Zn, Pb, and Cu. Various leaching agents, including citric acid, oxalic acid, tartaric acid, lactic acid, and deionized water, were tested for their effectiveness for removing Cr and Ni heavy metals, and oxalic acid showed the best leaching performance. The optimal leaching conditions were determined to be a concentration of 0.3 mol/L, a 6-h leaching time, and a solid-liquid ratio of 1:20, resulting in significant removal rates of Cr and Ni. The study also analyzed the distribution characteristics of Cr and Ni using the BCR sequential extraction method and investigated the removal mechanism of these heavy metals in oxalic acid leaching desulphurization sludge. These findings offer valuable insights for resource utilization and environmentally safe disposal of desulphurized sludge, particularly to mitigate environmental risks associated with Cr and Ni combined pollution.

Lithium and cobalt recovery from spent battery cathode by acid-reductive leaching using molasses: optimisation by response surface methodology

ABSTRACT The combination of molasses and sulphuric acid is reported for the first time as a leaching agent for lithium and cobalt recovery from spent lithium-ion batteries. The acid-reductive leaching process was optimised using a design of experiment with four input variables: sulphuric acid concentration, molasses concentration, leaching temperature, and leaching time. A response surface model with a central composite design determined the number of experiments, followed by quadratic regression modelling to analyze the relationship between input parameters and leaching recovery. ANOVA assessed the statistical significance of each variable, regression modelling, and optimal leaching conditions. The analysis showed temperature significantly affected lithium recovery, while both temperature and sulphuric acid concentration influenced cobalt recovery. The optimal conditions achieved 97.76% lithium and 99% cobalt recovery (2.5 M sulphuric acid, 60 g/L molasses, 54°C, 108 min). These findings highlight an eco-friendly and efficient approach to metal recovery.

Leaching of rare earth elements from phosphogypsum via citric acid medium: optimization through central composite design and kinetics studies.

Due to limited resources of rare earth elements (REEs) and their high demand, these are subjected to supply constraints. So it is important to recover REEs from potential secondary resources. Phosphogypsum is the waste generated on an enormous scale (300 million metric tons per year) from the fertilizer industry. It contains valuable REEs and its disposal has become a major environmental issue. The aim of this research work is to optimize the leaching parameters and determine the kinetics of leaching of REEs from phosphogypsum waste using citric acid. Response surface methodology (RSM) through central composite design (CCD) has been used to assess the influence of three key input variables, i.e., leachant concentration, temperature, and leaching time on the dissolution efficiency of REEs. The results of regression analysis and response surface plots revealed that with the increase in citric acid concentration as well as leaching time, the dissolution ratio of REEs would increase significantly. Under the optimum leaching conditions of 2mol/L citric acid, 343K temperature, and leaching duration of 180min, 90.11% dissolution efficiency was achieved. The kinetics of the leaching was elucidated with the use of shrinking sphere model and was found to be diffusion-controlled. This shows that the high leaching of REEs under moderate conditions is attainable, offering eco-friendly citric acid as a substitute to recover these critical elements from PG waste. The present work tends to develop efficient leaching protocols for the recovery of REEs, which are indispensable raw materials in numerous technological applications.

Selective extraction process of scandium from nickel laterite waste through hydrometallurgy.

Scandium (Sc) extraction from iron and aluminum waste is a promising technique for the recycling and valorization of laterite nickel ore waste. Iron and aluminum waste is one source of scandium during preparation of nickel and cobalt hydroxide by wet smelting of laterite nickel ore. The content of Sc is notably higher than that of the raw materials, as the element is enriched in the iron and aluminum waste. As the main element in the waste samples, Al exhibits significant interference in the selective separation of Sc. In this work, taking the production line for laterite nickel ore wet leaching as the research object, the trend and distribution of trace Sc were systematically analyzed. A series of leaching experiments was conducted under varied conditions of leaching pH (2.6-3.5), leaching time (0.5-2.0 h), volume of evaporated concentrated solution (0.2-1.0 L), mass of waste added (200-800 g), reaction temperature (240-260 °C), reaction time (0.5-1.5 h), H2SO4 addition amount (50-300 mL L-1) and (NH4)2SO4 addition amount (150-350 kg m-3). Experimental results revealed that the optimum leaching conditions were observed at a pH value of 3.0 and a leaching duration of 1 h. The optimum condition for evaporation and concentration was at 0.35 L, while the optimum conditions for impurity removal were at a waste mass of 300 g, a reaction temperature of 255 °C and a reaction time of 1 h. Under these optimum conditions, scandium content was approximately 14.67%. The product was identified as a complex salt of Sc through XRD, which could be converted to high-purity Sc2O3 after roasting.

Recovery of iron as hematite and separation of trivalent lanthanide ions from spent hard disk magnet leach liquor using [P66614][Cy272] ionic liquid.

The widespread use of neodymium-iron-boron (NdFeB) magnets has raised concerns about the environmental impact of their disposal, prompting the need for sustainable recycling strategies. Traditional solvents used in recycling are toxic and flammable, making them risky to use. Ionic liquids are safer and greener options with low vapor pressure, high stability, and less flammability. This study introduces an eco-friendly recycling approach utilizing the [P66614][Cy272] ionic liquid to selectively extract iron and recover rare earth elements (REEs) from the leach liquor of waste NdFeB magnets. Pre-treatment processes enhanced metal concentration before leaching, including demagnetization, grinding, and screening. Optimal leaching conditions: 2 mol L-1 HCl, 80 °C, 10 g L-1 pulp density, and 90 minutes, resulted in complete leaching of REEs (Dy, Pr, Nd), iron, and boron. Using 0.01 mol L-1 [P66614][Cy272] ionic liquid, 100% of the iron was removed from the leach liquor with minimal co-extraction of REEs (∼4%). Precipitation of iron leading to Fe2O3 (hematite) after calcination and is verified through XRD and SEM-EDS analyses. The ionic liquid also enabled 81.1% recovery of HCl from the leach liquor, reducing neutralization needs and operational costs. Subsequent REEs separation using 0.01 mol L-1 [P66614][Cy272] ionic liquid demonstrated high selectivity, achieving separation factors of 18.55 (Dy/Pr) and 15.52 (Dy/Nd) at pH 2.03. Dy(iii) was successfully separated from NdFeB leach solutions using counter-current extraction, leaving 6.0 mg L-1 in the raffinate, requiring two extraction stages at a 2 : 3 organic-to-aqueous phase (O/A) ratio. The reusability of the ionic liquid further enabled a sustainable, closed-loop recycling process. This approach highlights the potential for integrating ionic liquids into green technologies for NdFeB magnet recycling, ensuring resource recovery while minimizing environmental impact.

Effective recycling of mixed spent lithium ion batteries using sodium persulfate, and saponified Cyanex 272

ABSTRACT The presence of critical metals like lithium, manganese and cobalt is crucial in recycling spent lithium-ion batteries (SLIB). This study focuses on recovering these metals from SLIB powder through leaching, precipitation and solvent extraction. Key parameters affecting process efficiency were evaluated, along with the mechanism and kinetics of metal recovery. Optimal leaching rates of 96.8% lithium, 99.1% manganese, and 97.9% cobalt were achieved using 27% (v/v) HCl at 70°C and 10% (w/v) pulp density over 2 hours. Manganese was selectively precipitated with sodium persulphate at pH 1.3 for 4 hours. Lithium and cobalt were separated from the Mn-free solution using Na-Cyanex 272 at equilibrium pH 5.5, yielding a cobalt separation factor of 80.5. The McCabe-Thiele plot indicated two extraction stages with an aqueous-to-organic ratio of 1:1, achieving 99.6% cobalt extraction and 8% lithium co-extraction. Cobalt was back-extracted with 6% (v/v) HCl. The proposed process flow sheet offers a simple, effective method for metal recovery, supporting recycling businesses in extracting valuable resources efficiently.

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.

Highly efficient resource recovery from polymetallic sulfide ores under neutral-alkaline conditions: Chemical oxidation and coordination leaching

Nickel (Ni), cobalt (Co), and copper (Cu) are commonly co-associated in polymetallic sulfide ores, which typically contain substantial amounts of Ca and Mg as alkaline gangue. This composition presents significant challenges for economic recovery via conventional flotation-pyrometallurgical or acidic leaching techniques. This study introduces a novel neutral-alkaline lixiviant system based on the principle of “oxidation-coordination” to recover valuable metals from alkaline gangue-type polymetallic sulfide ores. Under optimal leaching conditions, the leaching extents of Ni, Co, and Cu from Jinchuan ore (200-mesh) achieved 87.7%, 81.5%, and 74.7%, respectively, whereas the dissolution rates of Ca and Mg impurities were limited to only 2.2–5.2%. During the ore oxidation stage, the advanced oxidation system formed by the activation of peroxydisulfate by both the original minerals and the leaching liquor plays a crucial role. In the coordination leaching stage, nitrilotriacetic acid (NTA) selectively coordinated with Ni, Co, and Cu, minimizing the dissolution of impurity metals. This study provides a theoretical foundation for the efficient and environmentally friendly utilization of alkaline gangue-type polymetallic sulfide ores.

Effect of H3PO4 coordination on vanadium extraction and iron separation in a H2SO4 leaching system.

The selectivity of the full wet leaching process for vanadium extraction using H2SO4 is low, resulting in a high impurity content in vanadium extracted from vanadium-bearing shale. This study focused on vanadium extraction and iron separation from vanadium-bearing shale, involving the coordination of H3PO4 in an H2SO4 leaching system. The effects of the ratio and quantity of H2SO4-H3PO4, leaching time, leaching temperature, and liquid-to-solid ratio on vanadium-bearing shale leaching were investigated. The dissolution processes of various minerals and the mechanism of iron coordination precipitation were analyzed. Results showed that vanadium leaching efficiency was 91.07% and iron leaching efficiency decreased from 84% to 23.86% under optimal leaching conditions-H2SO4-to-H3PO4 ratio of 2 : 1, H+ content of 8 mol kg-1, liquid-to-solid ratio of 0.8 L kg-1, and leaching time of 12 h at 95 °C. Leaching kinetics showed that the leaching process of vanadium shale was a mixed-control process in the H3PO4-H2SO4 leaching system; additionally, the leaching process was mainly controlled by a chemical reaction with an activation energy of 67 kJ mol-1. The preferential dissolution order of minerals in the vanadium-bearing shale was calcite, apatite, magnetite, muscovite, and pyrite. Under the H2SO4-H3PO4 leaching system, the iron content was reduced by inhibiting the dissolution of pyrite and coordination precipitation of Fe3+ with PO4 3-, thus separating iron and vanadium from the source. This provides guidance for vanadium extraction and impurity separation from vanadium-bearing shale using an all-wet method.

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.

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.

Study on the thermal field material of FZ-Si crystal waste graphite purified by ultrasonic enhanced acid leaching

This study examines the acid-leaching and purification process of waste graphite in the production of Czochralski monocrystalline silicon. The optimal leaching conditions are identified as a liquid-to-solid ratio of 6, a leaching temperature of 70 °C, an acid concentration of 8 mol, and a leaching time of 60 min. The use of hydrofluoric acid, sulfuric acid, and nitric acid in the acid-leaching process increases the fixed carbon content of waste graphite from ∼94 % to ∼98.5 %. To address the low fixed carbon content that cannot be achieved through conventional acid-leaching, a method combining ultrasonic intensification with hydrofluoric and hydrochloric acid leaching is proposed and successfully implemented. Under ultrasonic enhancement conditions, the leaching effect is optimal at a temperature of 60 °C, acidity of 4 mol, and leaching time of 60 min. These results demonstrate that the introduction of ultrasound significantly strengthens the acid-leaching process. The method proposed in this study not only purifies waste graphite through acid-leaching but also elucidates the reaction behavior of various impurity elements during the leaching process. Overall, these findings provide a foundational basis for the recovery of waste graphite in the thermal field.

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.

Bromic acid-thiourea synergistic leaching of sulfide gold ore

Abstract Bromate–thiourea coordinated leaching of gold sulfide ore for gold sulfide ore as leaching object. The effects of leaching reagent, stirring speed, and leaching time on gold leaching were investigated in this article. The results showed that the optimum leaching conditions were potassium bromate 0.1 M, thiourea 0.6 g·L−1, hydrochloric acid 0.2 M, agitation speed 250 rpm, ratio of liquid to solid 4, and leaching time 10 min. Under these conditions, high efficiency and rapid leaching of gold can be achieved, and reagent consumption is reduced. The research results have theoretical and practical significance for expanding new green gold extraction technology.

Iron removal from red clay using oxalic acid leaching for enhanced ceramic industry applications

This work focused on removing iron with oxalic acid from red clay samples collected from Kapasia Upazila, Gazipur District, Bangladesh. To characterize the red clay, the study employed several techniques: particle size analysis, WDXRF (wavelength-dispersive X-ray fluorescence), AAS (atomic absorption spectroscopy), XRD (X-ray diffraction), TGA (thermogravimetric analysis), and FESEM (field emission scanning electron microscopy). Additionally, leaching experiments were conducted with varying concentrations of oxalic acid, temperatures and times. After leaching, the red clay composition changed significantly: SiO₂ increased from 53.6 % to 63.13 %, Fe₂O₃ decreased from 17.1 % to 3.64 %, Al₂O₃ remained relatively stable at 18 %–18.22 %, and other oxides showed minor variations. 78.71 % of the iron was removed at optimal leaching conditions (1.0 M oxalic acid, 100 °C, 150 min, and 250 rpm). Mineralogically, the red clay samples are composed of illite, kaolinite, quartz, feldspar, hematite and chlorite. Thermal analysis showed significant weight loss at temperatures between 300 and 600 °C. Ceramic trials were conducted at firing temperatures of 900 °C and 1100 °C to evaluate the mechanical properties of tiles. The results obtained showed significant improvements in red clay quality for ceramics. Being a low-cost and eco-friendly process, this becomes a very prominent alternative to conventional iron removal techniques and helps produce high-quality ceramic tiles, contributing towards economic growth in Bangladesh.

High-efficiency leaching process for selective leaching of lithium from spent lithium iron phosphate

With the arrival of the scrapping wave of lithium iron phosphate (LiFePO4) batteries, a green and effective solution for recycling these waste batteries is urgently required. Reasonable recycling of spent LiFePO4 (SLFP) batteries is critical for resource recovery and environmental preservation. In this study, mild and efficient, highly selective leaching of lithium from spent lithium iron phosphate was achieved using potassium pyrosulfate (K2S2O7) and hydrogen peroxide (H2O2) as leaching agents. The leaching rates of lithium and iron were 99.83 % and 0.34 %, respectively, at the optimal leaching conditions of 4 vol% 30 wt% H2O2, 0.08 mol/L K2S2O7, 25℃, 5 min, and a solid–liquid ratio of 20 g/L. Meanwhile, the mechanism of the leaching process was explored by thermodynamic, XRD, XPS, FTIR, and SEM analyses. The leaching solution was concentrated and purified, with the addition of potassium carbonate (K2CO3) to convert lithium into lithium carbonate (Li2CO3). A small amount of sulfuric acid (H2SO4) is added to the saline wastewater after precipitation, which can be converted into a leaching agent for recycling after heat treatment. This study provides a sustainable green process for the recovery of lithium iron phosphate and a new idea for resource recovery.

Development of a process for extracting rare earth elements from phosphogypsum by dissolving them in deep-eutectic solvent

ABSTRACT The exploitation of deep-eutectic solvents (DESs) offered a potential substitute for water-based solutions when it came to leaching REEs from phosphogypsum (PG). The REEs leachate from PG obtained by DES which comprised choline chloride (ChCl) and diglycolic acid (DGA) or lactic acid (LA). The data offered a successful method for REEs leaching by DES ChCl:LA. The optimal leaching conditions included 150 min, 70°C, ChCl:LA 1:2 molar ratio of 800 rpm, a 15:1 L/S ratio, and 15% additional water. Cyanex 923 was used to assess REEs extraction from DES leachate. The best parameters were 900 rpm, 0.8 M Cyanex/toluene at 25°C, with 15 min extraction time and 1/1 A/O ratio. The REEs were stripped from the REEs/Cyanex after equilibrating for 20 minutes using 0.7 M citric acid, 1/2 A/O ratio, and 1000 rpm at 25°C. The RE ions precipitated from the obtained stripping solution by 30% oxalic acid and pH 1. The RE oxalate was precipitated and then burned at 700°C to gain RE oxide. The RE oxide powder was subjected to analysis to determine the REEs; it was possible to determine that the REEs were 80.98% in RE oxide concentrate, resulting in a purity of 94.76%.

Enhanced Recovery of Lithium and Cobalt from Spent Lithium-Ion Batteries Using Ultrasound-Assisted Deep Eutectic Solvent Leaching

This study investigates the ultrasound-assisted leaching of Li and Co from spent batteries using a deep eutectic solvent (DES) composed of polyethylene glycol and thiourea. The synergistic effect of ultrasound and DESs was explored to enhance the efficiency of Li and Co recovery. The experimental results demonstrated that ultrasound significantly accelerates the leaching process, achieving up to four times higher recovery rates compared to traditional methods. Optimal leaching conditions were identified at a solid-to-liquid ratio of 0.02 g/g, a temperature of 160 °C, and periodic ultrasound exposure. Under these conditions, the leaching efficiency reached 74% for Li and 71% for Co within 24 h. A kinetic analysis revealed that the ultrasound application shifts the rate-limiting step from a mixed control of mass transfer and chemical reactions to predominantly chemical reaction control, reducing the activation energy by approximately 27%.

Separation of valuable metals from low nickel matte to prepare NiCo2O4 materials: Optimization of oxidative leaching process and improvement of electrochemical properties of materials

The economical and efficient utilization of intermediate low nickel matte has become an important goal of nickel smelting industry. In this work, an innovative process of oxidative leaching of valuable metal from low nickel matte to prepare NiCo2O4 materials was proposed based on the materials utilization of mineral. The addition method and speed of ammonium persulfate in the oxidative leaching process was investigated to improve the extraction of valuable metals. The key factors affecting the leaching of valuable metals and the optimum leaching condition were determined by orthogonal experiments, and the extraction of Ni, Cu, and Co was 92.3 %, 97.1 % and 96.6 %, respectively. The leaching mechanism was clarified and the advantages of the leaching process were compared and analyzed. The kinetics of oxidative leaching process was studied by timing sampling method, and the control model, activation energy and kinetic equation of Ni, Cu and Co leaching were determined by analyzing the data with unreactive shrinkage model. The effects of Ni:Co ratio and calcination temperature of precursor on the properties of NiCo2O4 were investigated using the leaching solution removing iron and copper as raw materials. The NiCo2O4 material with the Ni:Co ratio of 1:2 prepared by calcining precursor at 750 ℃ for 3 h has a specific capacitance of 864F/g when the current density is 1 A/g. The prepared NiCo2O4 materials show good capacitance performance and has potential to be used as capacitor electrodes. This work combines metal extraction with product materialization, which is expected to help the metallurgical industry effectively shorten the industrial production process and reduce production costs.

Nitrogen recovery from biogas slurry with high ammonia nitrogen concentration through struvite precipitation utilizing acid leaching solution of collophanite tailings

ABSTRACT The high concentration of ammonia nitrogen (NH4+) and chemical oxygen demand (COD) in biogas slurry pose great challenges to the efficiency of traditional wastewater treatment systems. Collophanite tailings are solid waste, characterized by significant concentrations of phosphorus (PO43-) and magnesium (Mg2+), represent a potential resource for the reduction and recovery of NH4+ in biogas slurry via struvite precipitation. This study systematically explored the optimal leaching parameters employing sulfuric acid for the extraction of PO43− and Mg2+ from collophanite tailings. The effect of [PO43-]:[NH4+] molar ratio and pH on the recovery of NH4+ in biogas slurry was investigated. The physicochemical properties of the precipitates were confirmed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis. Results suggested that the highest removal efficiency of NH4+ (88.5%) was achieved when employing a [PO43-]:[NH4+] molar ratio of 1.0 at pH 9.5. Evaluation of effluent quality demonstrates a significant enhancement in the biodegradability of the treated biogas slurry, evidenced by an increase in the COD/TN ratio increased from 2.1 to 10.4. Economic analysis shows that the net income would be approximately 21.33 USD/m3 for proposed produces. These findings underscore the potential of utilizing collophanite tailings for NH4+ recovery from biogas slurry.