China Nonferrous Metallurgy

Abstract:The spent carbon cathode(SCC) generated during the overhaul of aluminum reduction cell has been classified as hazardous solid waste, which contains C, F, Al and other valuable components with high recovery value,so it must be disposed of reasonably. Harmless treatment and resource utilization can reduce environmental pollution in the aluminum electrolysis industry, fostering its green and efficient circular development. This paper examines the emission patterns and resource-environmental characteristics of spent carbon cathode, with a focus on both pyrometallurgical and hydrometallurgical treatment methods. It reviews the comprehensive recycling approaches, highlighting pyrometallurgical processes such as microwave-assisted high-temperature roasting, vacuum roasting, and ultra-high-temperature graphitization, as well as hydrometallurgical methods like flotation, chemical leaching, and water leaching. Pyrometallurgical processes offer high processing capacity and simple flow but result in the combustion of significant carbon materials and flue gas emissions during roasting. In contrast, hydrometallurgical processes provide high-purity carbon recovery, large treatment capacity, and efficient resource utilization, though they face secondary pollution from managing complex acid-alkali wastewater. Future the harmless treatment of SCC should focus not only on pollution control but also on recovering valuable components and producing multi-purpose products to achieve a pollution-free, low-cost, low-energy, and high-value recycling outcome.

Abstract:Rare earth metals and their alloys have become essential strategic resources in today's society, and they are mainly prepared by molten salt electrolysis. This paper introduces the research progress on the electrolytic preparation of rare earth metals and their alloys by high-temperature molten salt and room-temperature molten salt (ionic liquids) systems. Regarding the high-temperature molten salt system, it introduces the electrolytic preparation of rare-earth metals by chloride molten salt and fluoride molten salt systems, the electrolytic preparation of rare-earth alloys by different cathodes (inert cathode, active solid cathode, active liquid cathode), and the research progress of China's rare-earth molten salt electrolysis on electrolytic cell, automation and intelligent technology. Regarding the ionic liquids system, the research progress on the electrolytic preparation of rare-earth metals and their alloys by several types of ionic liquids, such as halogen metalate type, air and water stabilized type, task-specific type, and deep eutectic solvent, is introduced. In the high-temperature molten salt system has been realized in a variety of rare earth metals and their alloys of industrial production, but with the “carbon peaking and carbon neutrality goals” strategy continues to promote, rare earth electrolysis, high energy consumption, high emissions of the problem is imminent, the development of energy-saving, environmentally friendly rare earth electrolysis of the new process and equipment is the direction of the future development of rare earth electrolysis. Ionic liquids system electrolysis products are mostly particles or thin films, the preparation of bulk metal is still difficult, continue to develop low-cost ionic liquids with low viscosity, high salt solubility, high stability and other excellent physicochemical properties, for the preparation of low-temperature electrolysis of rare earth metals and their alloys is of great significance.

Abstract:The production and stockpiles of copper slag in China continue to increase, posing significant challenges for large-scale treatment. Copper slag contains valuable elements including copper, iron, lead, and zinc. Most enterprises employ a slow cooling-grinding and flotation process to recover copper, while iron (with content exceeding 40%) and other resources in the resulting tailings remain largely abandoned. Numerous scholars have investigated the resource utilization of copper slag, with existing methods primarily encompassing beneficiation enrichment, hydrometallurgical leaching, pyrometallurgical treatment, direct utilization processes, and combined processes. Iron in copper slag primarily exists in the form of fayalite and magnetite. The magnetic concentrate obtained through magnetic separation often contains elevated levels of lead and zinc, making it unsuitable for direct application in blast furnace production. Although direct resource utilization represents an effective approach for large-scale copper slag utilization, the fluctuating composition of copper slag complicates this strategy. Controversies persist regarding the environmental release of arsenic and other hazardous elements during applications such as building materials, cement production, and mine backfill applications. The critical challenge for iron recovery lies in decomposing the fayalite. Methods such as alkali leaching-acid decomposition and reduction/oxidation treatments can effectively decompose and transform the fayalite phase, enabling subsequent iron recovery through smelting or magnetic separation processes. Nevertheless, treatment processes must account for the impacts of harmful elements like arsenic on both iron extraction efficiency and product quality. The integration of multiple processes emerges as an effective strategy to achieve comprehensive recovery of valuable components in copper slag while enabling tailings recycling. The combination of multiple processes serves as an effective approach for achieving comprehensive recovery of valuable components from copper slag and realizing resource utilization of tailings. Subsequent efforts should persistently strengthen research on theoretical frameworks for efficient copper slag recovery technologies, equipment research, and strategic development pathways. It is imperative to actively broaden application channels for comprehensive copper slag utilization, expand the scale of integrated utilization, and enhance the utilization efficiency of mineral resources.

Abstract:The titanium containing blast furnace slag and titanium extraction waste liquid contain various valuable metals. Recycling and utilizing them can not only solve environmental pollution problems, but also improve enterprise profitability by preparing industrial products during the recycling process. According to the leaching process, the titanium extraction waste liquid can be divided into sulfuric acid titanium extraction waste liquid, hydrochloric acid titanium extraction waste liquid, ammonium sulfate roasting sulfuric acid titanium extraction waste liquid, and nitric acid titanium extraction waste liquid. The waste liquid from sulfuric acid titanium extraction contains a large amount of Al³⁺, which is often extracted to prepare aluminum ammonium sulfate and aluminum hydroxide, and the waste acid is recycled for comprehensive utilization. However, the method of preparing by-products has a low aluminum removal rate, and the filtration of the resulting Al(OH)₃ colloids is difficult; For hydrochloric acid titanium extraction waste liquid, precipitation method is often used to recover metal ions, but this method ultimately treats the waste liquid containing Cl^-, which cannot achieve green discharge; The comprehensive utilization of ammonium sulfate titanium extraction waste liquid is often achieved through solvent recovery, solvent recycling, leaching, and crystallization separation of components such as aluminum and silicon, which has good industrial application value. However, this process requires high equipment requirements, and the flocculation product is a gel like liquid, which is difficult to filter; The method of preparing aluminum hydroxide, calcium carbonate, magnesium carbonate by precipitation and ammonium nitrate fertilizer by evaporating the mother liquor is commonly used for comprehensive utilization of nitric acid extraction waste liquid. This method does not consume nitric acid in the acid leaching process and has a simple process, which has good application prospects. In the future, while focusing on the efficiency of titanium element extraction, this field should also develop recycling processes for other valuable elements, research and develop more environmentally friendly treatment technologies such as biological leaching and electrochemical leaching, reduce the generation of harmful by-products, and achieve a more sustainable treatment process.

Abstract:Gallium is regarded as a crucial material for modern new energy and high-tech industries, with a growing demand. China's low rank coal reserves are abundant and associated with gallium metal, but China's low rank coal has the characteristics of high carbon-silicon content and low gallium content, which makes gallium leaching interference great, resulting in low leaching rate and difficult gallium separation. In this paper, a pretreatment process for the removal of carbon elements from low rank coal by Budor reaction is proposed, and on the basis of characterization analysis, TG-DSC analysis is carried out, and a single factor test of the CO₂ gasification and decarburization process of low rank coal is carried out, and the following main conclusions are obtained. The chemical composition of low rank coal is mainly carbon, oxygen, aluminium, silicon, gallium content is 13μg/g, and the main phase structure is kaolinite, quartz, calcite, hematite and organic matter. The mass loss of low rank coal in Ar atmosphere is about 29%, while the mass loss in CO₂ atmosphere is more than 75%, which is attributed to the Budor reaction in CO₂ atmosphere. Under the optimal decarburization conditions of 1100℃, 60minutes and CO₂ gas flow of 5L/min, the decarburization rate of low rank coal can reach 90.43%, and the gallium content is increased from 13μg/g to 99μg/g, which is 6.6 times enriched. In this method, the CO₂ waste gas generated in the industrial production process is used to convert the carbon resources that are difficult to be directly utilised in low rank coal into gas energy CO that is easy to collect and utilise, and the effective enrichment of gallium in low rank coal is realised.

Abstract:At present, the most widely used method for preparing titanium metal in industry is the Kroll method. However, the Kroll method has the disadvantage of discontinuous production, long process, high energy consumption, and high cost, which leads to the high price of titanium metal and limits the application of titanium. Therefore, it has important meaning to develop new titanium smelting technologies with continuous production, short process and low cost. Hydrogen-assisted magnesiothermic reduction method transforms the Ti-O solid solution into Ti-O-H solid solution by introducing hydrogen into the system, breaking the thermodynamic limit of magnesiothermic reduction of TiO2. In this research, high purity low oxygen titanium hydride was prepared by hydrogen-assisted magnesiothermic reduction method using TiO2 with particle size of 0.05mm at 650℃ for 2h. The destabilizing effect of hydrogen on Ti-O solid solutions was studied by thermodynamic calculations. The presence of hydrogen makes the process of magnesiothermic reduction of titanium dioxide much lower in temperature, shorter in time and more thorough in reduction. The effect of particle size on the oxygen content of the product was studied by single factor experiment. The results show that the larger the particle size, the lower the surface oxygen content of the product. However, too large particle size will lead to poor reduction effect of lattice oxygen. The deoxygenation of the reduction product is the removal of its lattice oxygen. This study can support the further development of the hydrogen-assisted magnesiothermic reduction method.

Abstract:The hydrochloric acid leaching process of magnesium reduction residue by silicothermic method was studied in this paper. A two-stage hydrochloric acid leaching process was established to avoid the adverse effects caused by the formation of silica gel in the leaching process. The optimum technological conditions of two-stage leaching are determined, which meet the requirements of the designed leaching rate. The experimental results show that the decomposition rate of dicalcium silicate can reach 98.7% under the conditions of initial acid concentration 3mol/L HCl, liquid-solid ratio 5L/kg and leaching time 60min. Under the conditions of initial acid concentration 2.4mol/L HCl, liquid-solid ratio 5L/kg and leaching time 30min, the leaching rates of calcium, magnesium, iron and aluminum can reach 99.15%, 96.45%, 58.43%, 90.21%, respectively. The efficient utilization of magnesium reduction slag is realized.

Abstract:To optimize the treatment process of secondary ammonia leaching residue from molybdenum smelting and enhance production efficiency, this study investigated the leaching efficiency and economic benefits of three treatment schemes for ammonia leaching residue: atmospheric NaOH+Na2CO3 leaching, oxygen-pressure Na2CO3 leaching, and low-temperature pressurized NaOH+Na2CO3 leaching. The following key conclusions were obtained. The molybdenum species in the ammonia leaching residue primarily consist of 6.73% molybdenum oxide, 0.67% molybdate, and 0.36% molybdenum sulfide. Oxygen-pressure leaching significantly shortens the leaching time and improves molybdenum recovery. Under optimized conditions, the molybdenum leaching efficiencies for the three schemes were 91.70%, 97.22%, and 94.21%, with residual molybdenum contents of 0.89%, 0.265%, and 0.60%, respectively. The oxygen-pressure Na2CO3 leaching scheme demonstrated the best performance. Its optimized parameters include a Na2CO3 concentration of 50g/L, liquid-to-solid ratio (L/S) of 4, temperature of 210℃, oxygen pressure of 0.5MPa, and leaching duration of 1h. Under these conditions, the operating cost for treating 1 ton of ammonia leaching residue is 1441 RMB, with a profit of 37300 RMB, which offsets the higher initial equipment investment compared to the other two schemes. The oxygen-pressure Na2CO3 leaching method offers advantages such as high molybdenum recovery, low reagent consumption, minimal impurity leaching, and significant economic benefits, providing a valuable reference for the treatment of molybdenum-containing ammonia leaching residues.

Abstract:Alkaline fuel cells have attracted much attention in recent years due to their high energy conversion efficiency, relatively low operating temperature, and green green environment-friendly advantages. However, the sluggish kinetics of oxygen reduction reaction (ORR) at the cathode is a key limiting factor for alkaline fuel cells. It is of great significance to develop ORR catalysts with high activity, stability and low cost. In this study, a novel cobalt-based catalyst with two-dimensional leaf structure, denoted as Co@NC-L-Co_xZn_y, was prepared by direct pyrolysis of precursors with different proportions of Cobalt-Zinc bimetallic as metal sources. The morphology and structure of the catalysts were characterized by SEM, TEM, SAED, EDS-Mapping, XRD, XPS, BET, ICP-MS, and Raman. The electrochemical performance of Co@NC-L-Co_xZn_y was tested in an alkaline environment. The results show that Co@NC-L-Co₃Zn₁ exhibits a leaf-like structure with excellent electrocatalytic activity and stability. The E_on-set and E_1/2 in 0.1mol/L KOH electrolyte are 0.918V and 0.853V, respectively. After running for 10000s by chronoamperometry (i-t), 87.3% of the initial current is maintained, and its performance is comparable to that of commercial catalytic material 20wt% Pt/C.

Abstract:Hydrogen storage alloys can significantly alleviate the problem of component leaching during intermittent power supply from electrolysis water hydrogen production using wind energy and solar energy. Compared with rare earth-based hydrogen storage alloys, vanadium-based solid solution hydrogen storage alloys have a unique reversible hydrogen absorption and desorption process at room temperature, which can more effectively prevent the leaching of electrode components during power outage.This paper starts from two aspects: enhancing the anti-intermittent power supply ability of the electrode and reducing the overpotential of hydrogen evolution. Using vanadium, titanium and nickel metal powders as raw materials, vanadium-based porous alloy hydrogen evolution materials were prepared by powder solid-state sintering method. The influence of the preparation process conditions on the surface morphology and hydrogen evolution catalytic ability of the materials was investigated.The results show that the thermodynamic calculation results indicate that the Ti2-Ni phase disappears at a temperature of 700℃, while the Ti-Ni phase reaches its peak content of approximately 26%. At temperatures ranging from 950℃ to 1000℃, the Ti-Ni phase melts and forms a liquid phase. Under the conditions of adding 30% ammonium bicarbonate as the pore-forming agent, a forming pressure of 150MPa, a sintering temperature of 950℃, and a holding time of 4 hours, the prepared vanadium-based alloy has good performance, with a porosity of 52.99% and an open porosity of 32.56%. This can provide more active sites for the hydrogen evolution reaction;The hydrogen evolution overpotential of this vanadium-based alloy is 268mV, the charge transfer resistance is 92.7Ω, and the electrochemical active surface area (ECSA) is 5.69cm2. The hydrogen evolution overpotential is lower than that of the iron sheet electrode and the copper sheet electrode.

Abstract:Palladium resource market in China has a large demand but lack of reserves. The recovery of secondary palladium resources is of great significance to the industrial development of our country. Palladium ash is the product of palladium containing secondary resources recovery. Establishing a rapid, accurate and easy-to-master detection method provides a strong guarantee for improving palladium recovery and trade. In this paper, the sample was melt with sodium peroxide at 750±10℃, The impurities are separated after palladium complexation by diketoxime is precipitated, and then through hydrochloric acid-hydrogen peroxide resolubilization of palladium butanedione oxime precipitated，the contents of palladium were determination by inductively coupled plasma emission spectrometry (ICP-OES) under optimal operating conditions. It is selection wavelength Pd340.458nm to result computation.The results of this method are highly consistent with alkali melt-telluriumco-precipitation, acid dissolution and volumetric method. The recoveries were 98.2%~100.8% and the relative standard deviation (RSD) was 0.36%~0.80% and the measurement range was 1%~15%. This method is a simple, efficient and accurate method.

Abstract:The treatment of uranium-containing wastewater by adsorption technology has the advantages of simple operation, green and clean, and excellent removal performance. The development of new adsorption materials with high efficiency and simple preparation is an important research topic in this field. Bimetallic hydroxides have the characteristics of simple synthesis and excellent adsorption performance, and have become potential adsorption materials for efficient treatment of metal ion-containing wastewater. However, the maximum adsorption capacity of cobalt-magnesium bimetallic hydroxides for uranium reported in the literature is only 9.84mg·g-1 and the cost is expensive. In this study, a new type of iron-barium bimetallic hydroxide adsorption material was prepared by one-step synthesis method. It was characterized and analyzed, and the single factor condition test was carried out to optimize the process parameters. The following main conclusions were obtained: The Fe-Ba bimetallic hydroxide is an irregular particle-like structure and has certain pores. It is mainly composed of Fe(OH)3, Ba(OH)2 and BaCO3, and is rich in hydroxyl and carbonate. The complexation of hydroxyl and carbonate to uranium is the main adsorption mechanism. The optimum conditions for the removal of U(VI) in wastewater by the adsorbent were temperature of 25℃, pH=5.5, solid-liquid ratio of 0.2g·L-1, and time of 50min. Under this condition, the removal rate of uranium in wastewater containing 10mg·L-1 U(VI) was 96.52%. The adsorption material is less affected by interfering ions and humic acid, and has certain selectivity for uranium in the treatment of wastewater containing U(VI) 10mg·L-1. The adsorption model analysis showed that the removal of uranium by the adsorbent was mainly monolayer and chemical adsorption, and the maximum adsorption capacity could reach 163.93mg·g-1. The adsorption material is suitable for the treatment of wastewater containing uranium 5~10mg·g-1, and has the advantages of simple preparation, no secondary pollution and low cost, and has industrial application value.

Abstract:As an important ore for extracting lithium, lepidolite will produce a large amount of fluorine-containing wastewater and leaching residue in the smelting process, which will cause serious pollution to the environment. In this paper, the lemica leaching residue was used as the basic skeleton and modified by high-temperature roasting and aluminum sulfate solution soaking to prepare a new type of defluorination material. The morphology and structure of the modified material were analyzed by SEM, TEM, XRD and FTIR, and its defluorination performance was studied by static adsorption experiment. The adsorption mechanism was studied by adsorption kinetics and isothermal adsorption line model. The results show that the modification does not remove fluorine from the leucite residue, and greatly changes the surface morphology and increases the number of active sites on the surface. Under the conditions of roasting temperature 450℃, roasting time 2h, concentration of aluminum sulfate solution (Al³⁺) 12g/L, dosage of adsorbent 5g/L, reaction temperature 25℃, initial concentration of fluorine-containing solution 5mg/L, and so on, the RAA adsorbent prepared by roasting-aluminum sulfate solution soaking-alkali modification was prepared for 1min. The defluorination rate reached 91.56%, the adsorption equilibrium was reached in 180min, and the final defluorination rate was up to 95.12%. The adsorption process was highly fit with Langmuir model and quasi-second-order kinetic model, that is, single-molecular layer adsorption and chemisorption were the main processes. The modified lemica leaching residue shows good adsorption capacity for fluorine in water and can effectively remove fluorine pollution, and the fluorine in the slag will not be removed during the modification process, so it can be applied to the treatment of other high fluorine groundwater.

Abstract:China produces a large amount of electric furnace Ferronickel iron slag (FNS), which has certain alkaline hydration activity and can be used as an auxiliary cementitious material. Ground granulated furnace slag (GGBS) has excellent hydration cementitious activity and is one of the best performing auxiliary cementitious materials. In order to maximize the utilization of FNS, this paper prepared active composite micro powder (CMP) by adding FNS into GGBS, and investigated its activation performance and mechanical properties. The main conclusions are as follows. Increasing the specific surface area of FNS can improve the mechanical strength of FNS-cement mortar specimens, but it will reduce toughness. When the proportion of FNS in the CMP is less than 20%, the CMP can meet the activity requirements of grade S105 GGBS. When the proportion is between 20% and 40%, it can meet the S95 level. The addition of FNS can reduce the grindability, so before mixing into CMP, the FNS needs to be pre-ground to a certain fineness. The addition of FNS can lead to early strength loss of mortar, but the its hydration activity gradually becomes apparent with increasing curing age. When the specific surface area of the CMP is between 410 and 432m2/kg, the activity can reach the level II composite admixture standard; when the specific surface area increases to 519m2/kg, the activity can reach the level I standard. The price of FNS is lower than that of GGBS, and adding FNS can reduce the production cost of CMP, but the proportion of addition should not exceed 20%. At this time, the cost can be reduced by about 10%, and it has good technical and economic efficiency.

Abstract:The high-temperature melting and harmless disposal of incineration fly ash can achieve the decomposition of organic compounds such as dioxins and the solidification of heavy metal elements. The degree of harmless disposal of fly ash is high, but the large amount of chloride salts contained in fly ash will greatly hinder the melting process. This article aims to separate slag and salt melting in fly ash, and designs and selects an ideal low melting point slag type, CaO-FeO-SiO2-Al2O3-Fe2O3 five element slag, CaO∶SiO2∶FeO∶Al2O3∶Fe2O3=36∶34∶21∶7∶2, the complete melting temperature of the slag is around 1250℃. The results of the hot state test indicate that the optimal slag ratio scheme effectively suppresses the volatilization of chloride salts while achieving efficient separation of slag and salt. After the melting and separation of slag salt, the proportion of Cl, Na, and K elements enriched in the molten salt phase reaches 76.40%, 97.54%, and 88.19%, respectively. Slag water quenching achieves solidification of heavy metals such as Pb and Zn. Compared with raw material fly ash, the leaching concentration of Pb, Zn, Cr and other elements in water quenched slag can be reduced by 99.48%, 90.00%, and 72.00%, respectively. The leaching toxicity test of water quenched slag meets the requirements of vitrified products. After separating fly ash salt, the tailings and incineration bottom slag can be co processed to prepare vitrified products, which can achieve “zero emission” of ash in the process of garbage incineration power generation.

Abstract:Aiming at the low oxidation rate and difficult utilization of magnesium flue gas desulfurization products, this paper studied the influence of the process system on the oxidation behavior of magnesium sulfite under pressure by using the method of forced oxidation of magnesium sulfite under pressure, and calculated the diffusion coefficient (D) of oxygen in solution by means of molecular dynamics (MD) simulation method, and explored the mechanism of system relative pressure (System pressure is 0.1MPa) on the diffusion behavior of oxygen in solution. The results show that high temperature and acidic environment in high pressure system can increase the diffusion coefficient of oxygen. In addition, with the increase of temperature, the oxidation rate of magnesium sulfite increased first and then decreased, and reached the highest when the temperature was 318K, while with the increase of pH value, the oxidation rate of magnesium sulfite decreased first and then increased, and reached the highest when pH=7.0. When the system relative pressure is 0.3MPa, the temperature is 301K and pH is 7.0, the oxidation rate of magnesium sulfite can reach 91.58%, and the oxidation rate is 3.99 times that of atmospheric bubbling reaction, which plays an important role in the resource utilization of magnesium desulfurization products.

Abstract:It is of great significance to explore the characteristics of the copper-containing phases in the slag to improve the utilization rate of subsequent resource recovery treatment such as high-temperature reduction, flotation and wet leaching. In this study, MLA, SEM-EDS and particle size analysis were used to reveal the existence of each copper phase in the slag and its relationship with each phase. The results show that the copper-containing phases in slag include Cu₂S、Cu₅FeS₄ Cu and CuSb, with contents of 3.01%, 0.28%, 2.38% and 0.04%, respectively. The main distribution intervals of the particle sizes of Cu₂S and Cu₅FeS₄ are 6.8~75μm (69.74%) and 3.4~27μm (79.46%), respectively. The proportion of metallic copper particles with particle size larger than 53μm was 58.4%.The particle size of CuSb particles was smaller, with 93.32% of the particles in the range of 6.8~38μm.Cu₂S and Cu5FeS4 were mainly in a consecutive or encapsulated state with Fe₃O₄, Fe₂SiO₄, and (Pb,Zn,Fe,Al,Ca,K)SiO4 in the slag, and the proportions of their free surface areas were respectively 79.57%, 74.74%. The natural Cu was consecutive with or encapsulated by Fe₃O₄ Fe₂SiO₄ Cu₂S, and partially encapsulated a small amount of PbS, with a free surface area ratio of 50.40%. CuSb was low in the slag phase and was mainly encapsulated by Cu₂S, Cu, Fe₃O₄ and Fe₂SiO₄ with a free surface area ratio of only 28.14%. The results provide a reference basis for the development of efficient separation and recovery process of different copper-containing phases in slag.