China Nonferrous Metallurgy

Abstract:The ionic liquids formed by 1-ethyl-3-methylimidazole chloride (EMIC) and 1-butyl-3-methylimidazole chloride (BMIC) with aluminum chloride (AlCl₃) are the most promising ionic liquids for electrolytic aluminum. In this paper, linear voltammetry, chronoamperometry, chronopotentiometry, constant-voltage electrolysis, constant-current electrolysis and other electrochemical experiments are used to compare the anodic dissolution of aluminum in acidic AlCl₃-EMIC and AlCl₃-BMIC ionic liquids under stirring and non-stirring conditions, in order to screen out a better electrolyte system. The effects of stirring, temperature, current density, potential and other process parameters on the electrolytic process are investigated to provide basic data for industrial scale-up.

Abstract:Calcined petroleum coke is an important raw material of metallurgical carbon materials such as carbon anode for aluminum electrolysis. The existing research lacks of in-depth exploration of the microstructure evolution of calcined coke at different calcination temperatures, which makes it difficult to intelligently control and reduce the consumption of metallurgical carbon production. In order to solve the above problems, an intelligent extraction technology of lattice fringes of carbon materials based on HRTEM detection and mathematical fitting were used to investigate the evolution law of the microstructure of calcined coke at different calcination temperatures. When the temperature was below 600℃, the average lattice fringe length, total stacking frequency, and 45° contribution of the calcined cokes slightly deteriorated with the increase of temperature. While in the temperature range of 600 to 1600℃, the variation patterns of the characteristic values were consistent with the Sigmoid function model, which increased rapidly and then gently with the increase of temperature. The effective temperature intervals of the microstructure characteristics were obtained via the deduced formula of the fitting curves. The priority of the microstructure characteristics changing with temperature was as follows: lattice orientation ＞ lattice stacking ＞ lattice growth. The graphitization degree R of calcined coke varied from 0.86 to 0.59 in the temperature range of 25~1600℃ by Raman spectrum analysis. The evolution law of graphitization degree at different temperatures demonstrated the result of the variation patterns analysis of the above microstructure characteristics.

Abstract:The electrolysis of lunar soil in cryolite molten salts can realize the in-situ preparation of metals and oxygen, and it is of great significance to study the initial crystal temperature of cryolite molten salts containing lunar soil for the stable operation of the electrolytic cell. In this study, NEU-1 lunar soil simulant prepared from volcanic slag and basalt was used as raw material, mixed with cryolite to obtain electrolyte, which is used as sample to be tested, and the initial crystal temperature of cryolite molten salts with different NEU-1 lunar soil simulant addition and molecular ratios was measured by differential thermal analysis. The results indicated that when the molecular ratio was 2.2, the initial crystal temperature of the cryolite molten salts decreased from 974.9℃ to 932.0℃ with the increase of the addition amount of lunar soil simulant from 0% to 24%. The initial crystal temperature of the cryolite molten salts decreased by 1.79℃ as every 1% of the lunar soil simulant was added. When the addition amount of lunar soil simulant was 8%, the initial crystal temperature of the cryolite molten salts increased from 960.0℃ to 979.4℃ with the increase of molecular ratio from 2.2 to 2.7.

Abstract:Aluminum alloy has the advantages of corrosion resistance, easy processing, high strength, low density and so on. It has a large number of applications in all walks of life. Aluminum alloy prepared by molten salt electrolysis method has the characteristics of simple production process, high efficiency, low production cost and short production cycle. In recent years, it has been widely concerned, among which the selection of molten salt system has become the main research hotspot. This paper divides molten salt system into high-temperature molten salt and ionic liquid by temperature. The advantages, classification and some reaction mechanisms of these two molten salt systems are reviewed. Based on both molten salt systems, the preparation process of some aluminum alloys and related technological innovations are introduced respectively. Finally, the advantages and disadvantages of high-temperature molten salt and ionic liquid are described respectively, and their future development trend is prospected.

Abstract:Inert anodes are an important research direction to keep primary aluminum production low-carbon, and in recent years, considerable progress has been made in the study of inert anode materials. By classifying inert anode materials, the possible corrosion reactions of different types (alloy anodes, oxide ceramic anodes and metal ceramic anodes) of inert anodes in molten salt electrolytes are reviewed, mainly exploring the chemical and electrochemical corrosion that occurs and the possible effects on the anode after corrosion. To clarify ways to increase the corrosion resistance of anodes or to reduce the corrosion rate of inert anodes in cryolite molten salt by inhibiting the corrosion reaction, the development of viable inert anodes in the aluminum electrolysis industry was promoted.

Abstract:Scandium is an important rare earth element widely used in structural materials such as alloys and ceramics, as well as functional materials such as fuel cell electrolytes and radio frequency filters. In this paper, the preparation methods of scandium fluoride and anhydrous scandium chloride are introduced successively, and then the metal thermal reduction process of scandium halide and the treatment methods of different impurities in crude scandium distillation and purification are described in detail. Then, the further purification and impurity removal methods using zone melting, electromigration and vacuum electron beam melting technologies are discussed. Comparing with calciothermic reduction technology with scandium fluoride, the magnesiothermic reduction technology with scandium chloride to prepare metal scandium has the advantages of low temperature, environmental friendliness and low cost. In the future, the research on the preparation of metal scandium can be focused on the metal thermal reduction of anhydrous scandium chloride. The impurity elements can be removed by multiple high temperature vacuum distillation and electron beam melting, so that the purity of metal scandium can reach 4N or even 5N level. Vacuum electron beam melting, relay zone melting and other technologies have broad development prospects in the preparation of ultra-high purity metal scandium and other rare earth metals.

Abstract:Zinc leaching residue from zinc hydrometallargy is a kind of solid waste with both resource endowment and environmental hazard. Treating zinc leaching residue is of great significance for resource recovery and environmental protection. Various zinc leaching residue treatment technologies have been successfully applied in China, such as hot acid leaching, rotary kiln volatilization, fuming furnace fuming, top blowing smelting, side blowing smelting, and sulfur dioxide reduction leaching. However, there is still a certain gap in meeting the requirements of solid waste reduction, resource utilization, and harmless treatment. In this paper, characteristics of residue generated in the zinc leaching process and present industrial treatment of zinc leaching residue were discussed from the perspective of solid waste reduction, resource utilization and harmlessness. The difficulties of treatment for zinc leaching residue were discussed. Finally, suggestions and prospects were put forward.

Abstract:High purity sputtering targets are used as consumables in wafer foundries and LCD panel companies. The utilization rate of high purity sputtering target is low. The utilization rate of general flat targets is less than 30%, and it is difficult for rotating targets to exceed 70%. It is of great economic value and environmental significance to recycle the sputtered residual target. The research status of recovery of high purity target materials such as precious metals, ITO, titanium, tantalum, aluminum and copper were reviewed, and common problems in the recovery process of target materials were summarized. At present, there are still problems that need to be overcome and improved in the residual target recovery of high-purity target materials, such as low metal recovery rate, low purity of recovery, and long process flow, so the author anticipates that developing shorter process, environment-friendly process and exploring high-value uses are the directions for the improvement and development of high-purity residual target recycling and reuse technology in the future.

Abstract:The recovery of tin from low-grade tin middling by reduction smelting method was studied, and the recovery behavior of tin was investigated when copper oxide was used as an additive. The results show that under a certain conditions, increasing the melting temperature, increasing the amount of coke addition, extending the holding time and increasing the amount of copper oxide addition can improve the recovery of tin, however, when the temperature is too high, iron oxide in the slag is reduced to metallic iron and alloyed with reduced metal tin to form Fe-Sn alloy, which has a high melting point and is easily entrapped in the slag during the separation of slag and metal resulting in the loss of tin. With copper oxide as an additive, it can generate metallic copper by reduction reaction and then alloy with metallic tin to form Cu-Sn alloy, which thermodynamically reduces the activity of Sn in the product and promotes the reduction and recovery of tin. Under the conditions of 7% coke addition, 5.8% copper oxide addition, 1250℃ melting temperature and 150min holding time, the recovery of tin can reach 95.24%, and tin is distributed in copper-tin alloy (distribution ratio 90.20%) and tin containing dust (distribution ratio 5.04%), which realizes efficient recovery of tin from low-grade tin-bearing middling.

Abstract:Aiming at the problems of long drying cycle and large process pollution of the current lead-zinc smelting slag, this paper proposes a new technology of microwave enhanced drying. On the basis of analyzing the physical properties of the raw materials, the high temperature dielectric and microwave drying factors of the neutralized lead-zinc smelting slag were analyzed, and the drying process mechanism of the microwave-enhanced neutralized lead-zinc smelting slag was clarified. The results show that the phase containing crystal water in the neutralized slag is CaSO₄·0.5H₂O, the content of free water is 30.2%, and the content of crystal water is 7.2%. The wave-absorbing properties of free water and crystal water are similar, and obviously superior to other phases in slag. Under the conditions of particle size 8cm, thickness 2.2cm, microwave power 700W, and drying time 15min, microwave drying has the best effect of neutralized lead-zinc smelting slag, free water is completely removed, the removal rate of crystal water reaches 53.06%, and the total water loss rate is 34.02%. When the neutralized lead-zinc smelting slag is dried by microwave, it will cause cracking and stratification of the neutralized slag, which helps to achieve fast and efficient drying. Compared with conventional drying, microwave drying 1kg neutralized lead-zinc smelting slag saves energy by 16.98% (630kJ), removes 5.40% more water than conventional drying, and shortens drying time by 87.5%. The drying technology of neutralizing lead-zinc smelting slag established in this paper has obvious advantages.

Abstract:With the gradual decline of copper concentrate grade, impurity elements gradually increase, and the harmful element arsenic is difficult to remove and accumulates in the copper smelting system, which has a great impact on the quality of copper cathode. Combined with the actual production of copper top-blown melting, the distribution ratio of harmful arsenic elements in the dust is 55%~75%, that in the matte phase is 5%~15%, and that in the slag phase is 20%~35%. In this paper, the distribution and direction of arsenic in the copper top-blown melting process is theoretically analyzed, and the influence law of process parameters such as Fe/SiO₂ in slag, oxygen-rich concentration, matte grade, CaO content in slag on the distribution rate of arsenic in different products is investigated under laboratory conditions, and effective control measures for arsenic entering the slag phase are obtained. After optimizing the process parameters, the proportion of As in slag is 30%~40%, the proportion in dust is 50%~60% and the proportion in matte is 10%~20%, which solves the problem that a large amount of arsenic enters the sulfuric acid system to form arsenic slag during copper smelting and improves the adaptability of raw materials, thus controlling the content of arsenic in each product.

Abstract:The copper anode mud smelting slag was an important rhodium resource. The rhodium in copper anode mud smelting slag was recovered by fire enrichment and wet extraction. The effects of various factors on the enrichment were investigated.Under the conditions of the addition of PbO 1.1 times wt. of smelting slag，the addition of B₂O₃1.1 times，the addition of Na₂CO₃ 0.9 times，1200℃ and 2h melting time, the Rh content of lead alloy was 7536.4g/t，and the enrichment times was 6.2；under the conditions that addition of silver was 1 time wt. of lead alloy, the ash blowing temperature was 1300℃, and the ash blowing time was 2.5h, the Rh content of silver alloy was 42208.1g/t , and the enrichment times was 35.7；under the conditions of leaching temperature 60℃, leaching time 1.5h and leaching liquid-solid ratio of 10∶1, the purity of rhodium powder was 91.2%, and comprehensive recovery of rhodium secondary resources was realized.

Abstract:The mixing and mass transfer performance of the multiphase system directly affects the multiphase reaction process. The team developed a new type of tubular stirred reactor that discharges gas from the impeller end. The steady-state sulfite method (FSM) was used to study the gas-liquid mass transfer performance of the reactor. The effects of ventilation flow rate Q, stirring Froude number Fr and liquid content on the volumetric mass transfer coefficient kLa were investigated. The results show that increasing Q and Fr can effectively improve k_La. The new inlet mode can enhance k_La, which is about 2 times higher than that of the traditional reactor. The gas-liquid mass transfer performance of the reactor is highest at ε=0.5, Fr=0.054, Q=1.6m³·h^-1, with k_La=0.0324s^-1. Based on the experimental data, a dimensionless correlation for k_La was established, and the error was basically within 25%, which has reference significance for improvement and application of the subsequent reactor.

Abstract:In the electrolytic process of rare earth molten salt, different electrification modes have different effects on the physical fields in the cell, which will also have a certain impact on the electrolytic efficiency of the cell. In this paper, the 8kA rare earth electrolytic cell of an enterprise is taken as the prototype, through the thermoelectric coupling module of Comsol, the single-side and multi-side power-on mode and the change of the internal parameters of electrolytic cell under the distribution of different positions of the electrified copper plate are studied to find the most suitable power-on mode. The purpose of this study is to provide reference for structure optimization of rare earth electrolytic cell. The results show that：when only the electrolytic efficiency is considered, the median distribution of the four sides of the conductive plate is the optimal structure, and the current density in the electrolytic cell is the highest, the electric energy loss is the lowest, and the electrolytic effect is the best. Considering the manufacturing cost and operability, the single-side median distribution of the conductive plate is the optimal solution. The electrolytic cell with this design has higher electrolytic efficiency and leaves more room for operation. The other distributions have drawbacks and need to be further better.

Abstract:The current quality inspection process of finished praseodymium and other rare-earth alloy ingots uses manual drilling method and chemical analysis method, which has defects such as long quality inspection period, high cost and serious reliance on manual experience. This paper proposes a non-destructive physical inspection method based on the technology of acoustic feature analysis, combined with the theory of sensors, signal processing and classical engineering control. Firstly, the smelting process of praseodymium alloy obtained by molten salt electrolysis is analyzed to determine that its carbon content index can be used as a classification characteristic of metal quality, and the acoustic signal can be relied on to determine the metal carbon content. Secondly, the acoustic signal of praseodymium alloy is collected when it is excited by external pulses, and the inner correlation model between the carbon content of praseodymium alloy and its acoustic signal characteristics is established by analyzing the time domain waveform of the acoustic signal. Finally, the results of the orthogonal experiments show that the time domain characteristics of the acoustic signal can better distinguish the difference between high and low carbon of praseodymium alloy.

Abstract:The removal of uranium from water is a topic that requires research due to its harmful effects on human health. Using low-cost CaCO3 and (NH4)2HPO4 as raw materials, hydroxyapatite (OP-HAP) was synthesized in a one-pot method and applied for the removal of uranium from solutions. The adsorption performance of OP-HAP on uranium was explored through single-factor and orthogonal experiments, and its characteristics were characterized using SEM, EDS, XRD, FTIR, and XPS. The results showed that under optimal conditions, OP-HAP achieved a maximum removal rate of around 97% for 10mg·L-1 uranium, with a fitted maximum adsorption capacity of 1584.79mg·g-1. The adsorption process of uranium by OP-HAP followed the Langmuir isotherm adsorption model and the pseudo-second-order kinetic model. Thermodynamic studies indicated that the adsorption process was endothermic and spontaneous. Characterization of the Zeta potential and OP-HAP before and after uranium adsorption revealed that the main mechanisms of adsorption were electrostatic adsorption, ion exchange, complexation, and dissolution precipitation. OP-HAP exhibited a high adsorption capacity for uranium and is a potential uranium adsorbent.

Abstract:The chromium in the electroplating sludge occurred mainly in forms of oxides and/or hydroxides, which could be recovered through a combined process of Na₂CO₃ assisted oxidizing roasting and water leaching in this research. The results show under the condition of Na₂CO₃ amount of 100%, roasting temperature of 700℃, and roasting time of 90min, the Cr recovery rate reached 97.8% in the subsequent water leaching process; in a certain range, the Cr recovery rate increased with the increase of Na2CO3 amount, roasting temperature and time; in the Na₂S reduction of Na₂CrO₄ leaching solution, the chromium yield increased with the increase of the amount of Na₂S addition, reaction temperature and reaction time; however, excessive Na₂S amount would increase the pH of the leaching solution, resulting in the reverse dissolution of Cr₂O₃ and the decrease of chromium recovery; under the optimized condition of reaction temperature of 60℃, n(CrO^2-₄)/n(S^2-) of 8∶9, and reaction time of 80min, the chromium recovery reached 92.3%. The study achieved an efficient recovery of chromium from electroplated sludge.

Abstract:Waste printed circuit boards are rich in metal and non-metal resources, which have high resource recovery value and potential environmental hazards. In this study, under the conventional and microwave pyrolysis conditions, the influence of the detinning pretreatment and related pyrolysis conditions on the distribution and mechanism of pyrolysis products were studied. The results show that detinning pretreatment has a positive effect on the pyrolysis of waste computer circuit boards, which can make the organic materials in the waste circuit boards pyrolyze more fully. After detinning pretreatment, the Sn content is reduced from 4.10% to 1.54%, and the recovery rate of Sn can be reached 68.49%. Under conventional and microwave pyrolysis conditions, more liquid and gas products can be obtained with the temperature increasing, but more solid products can be obtained by microwave pyrolysis at the same temperature.After conventional pyrolysis, the copper content increased from 19.17% before pyrolysis to 25.37%, and after microwave pyrolysis, the copper content increased from 19.17% before pyrolysis to 23.32%.And the recovery rate of copper is over 99.22%. After pyrolysis, most of the bromine element enters the pyrolysis oil and pyrolysis gas. The content of phenolic in microwave pyrolysis oil is greater than that of conventional pyrolysis, and the content of furans is less than that of conventional pyrolysis. The pyrolysis gas contains a large amount of combustible gas. The total amount of H₂, CO and CH₄ in the conventional and microwave pyrolysis gas reach 76.4% and 80.7%, respectively. The heating value of the pyrolysis gas is 18.78MJ/Nm³ and 19.97MJ/Nm³, respectively. The calorific value of pyrolysis gas is between coal gas and natural gas and can be used as gas. Comprehensive comparison between conventional pyrolysis and microwave pyrolysis, microwave pyrolysis has a higher metal recovery rate, less furans in the pyrolysis gas, and a higher calorific value of the pyrolysis gas, which is more conducive to the comprehensive recovery of valuable metals in electronic waste use.