China Nonferrous Metallurgy

Abstract:Aluminium slag belongs to hazardous waste generated by the aluminium industry， containing a large amount of Al， while impurity elements such as Ca， Si， and Mg limit its high-value utilisation. Based on the mechanism that Fe， Ca， Si， Mg and other elements can form pyroxene-type magnetic substances which can then be removed by magnetic separation， this study adopts a roasting-magnetic separation process to investigate impurity removal from aluminium slag. Thermodynamic software was used for analysis to obtain the appropriate elemental ratio for forming pyroxene-type magnetic substances， and aluminium slag was then prepared according to this ratio； the effect of temperature on the roasted products of the prepared aluminium slag was studied， and thermogravimetric-differential thermal analysis and characterisation analysis were used to explore the phase reconstruction characteristics； finally， magnetic analysis was conducted to verify the formation of pyroxene-type magnetic substances. the main temperature range for the formation of iron-bearing pyroxene-type magnetic substances is concentrated between 1 100-1 300℃. Under the roasting temperatures of 1 250℃ and 1 350℃， the roasted products of the prepared aluminium slag were Ca（Fe， Mg）Si₂O₆ and Ca（Mg， Fe， Al）（Si， Al）₂O₆， respectively； magnetic analysis of the generated pyroxene substances showed that they have soft magnetic material characteristics， with remanent magnetisation of 0. 12 T and 0. 07 T at temperatures of 1 250℃ and 1 350℃ respectively， meeting the requirements for magnetic separation processes. The aluminum ash slag was used for roasting verification， and the test results were consistent with the prepared aluminum ash slag. That is， the Ca， Si， and Mg impurities in the aluminum slag can generate magnetic material pyroxene products， which are separated from the roasted sample by magnetic separation process. After magnetic separation at 1 250℃ and 1 350℃， the content of SiO₂， CaO and Fe₂O₃ in aluminum slag decreased （the proportion of magnetic substances at 1 250℃ was 6. 5%， and the proportion at 1 350℃was 5. 3%）. The aluminum ash after magnetic separation can be used as high aluminum material in the field of advanced ceramics. The results show that the roasting process of aluminum slag can generate magnetic substances， and the impurity removal and quality improvement can be further realized， which provides a new idea for the high-value utilization of aluminum slag.

Abstract:In view of the frequent ringing problem in the process of secondary aluminum dross smelting in rotary kiln， this study used low-salt secondary aluminum dross as raw material for sintering experiment. The densification sintering temperature and the composition volatilization temperature were determined by thermogravimetric analysis， high temperature deformation analysis and the relationship between liquid volume and volatile matter and temperature. A two-stage roasting process was proposed and verified. When the rotary kiln roasts the low-salt secondary aluminum ash， the main reason for the ringing phenomenon is the excessive liquid phase generated at the high temperature stage. At 710℃， the secondary aluminum dross emits a lot of heat due to violent combustion， which leads to the rapid heating of the local micro-area to produce liquid phase， which promotes the densification of sintering， and the densification is completed at 850℃. At 939. 5-1 194. 9℃， Cl， F， K， Na and other elements volatilize. With the increase of temperature， the total liquid phase increases first and then decreases， reaching a maximum of 10. 66% at 1 000℃， and the total molten salt liquid phase decreases to 7. 16% at 1 300℃. The twostage roasting process， i. e. low-temperature roasting at 850℃ for 3 h， is used to complete the balling densification and let the nitrogen escape smoothly. The purpose of high temperature roasting at 1 300℃ for 3 h is to concentrate and volatilize Cl， F， K， Na and other salt elements that easily lead to ring formation. The verification test showed that compared with single temperature roasting， the ring quality under two-stage roasting （850℃，3 h；1 300℃， 3 h） is only 0. 41 g， which is 28. 07% lower than that of scheme 1（850℃，3 h） and 14. 58% lower than that of scheme 2（1 300℃，3 h）， and the effect of inhibiting the ring formation is obvious. After two-stage roasting， the content of Na and Cl in the sample decreased to 1. 21% and 0. 03%， respectively， and Al₂O₃ increased to 81. 44%. In addition， the mass fraction of Cl， K₂O， SO₃ and F also decreased significantly， and the roasting effect was better. The results of this study provide theoretical guidance and technical reference for the ringing formation inhibit in roasting of low-salt secondary aluminum dross by rotary kiln.

Abstract:The harmless treatment and resource utilization of secondary aluminum dross have become increasingly urgent due to its massive production， low-added-value applications， and insufficient basis for large-scale effective utilization. Secondary aluminum dross is mainly composed of oxides of aluminum， silicon， magnesium， aluminum nitride and other components， which show a high compositional matching degree with cordierite， thus possessing raw material advantages for preparing cordierite composite porous ceramics. In this study， secondary aluminum dross was used as the main raw material， with silicon dioxide and magnesium oxide as additives， to prepare cordierite composite porous ceramics by solid-state reaction sintering. Firstly， the desalination process was optimized through low-temperature roasting， then the effects of sintering temperature and holding time on the microstructure， phase composition and properties of the ceramics were systematically investigated . The results show that 750℃ for 6 h is the optimal desalination process， which can effectively remove soluble salts while retaining the aluminum nitride pore-forming component. Sintering temperature and holding time significantly affect the firing loss rate， phase composition and properties of the ceramics. The firing loss rate reaches the minimum value of 6. 38% at 1 350℃ for 3 h. With the increase of sintering temperature and the extension of holding time， the cordierite phase in cordierite composite porous ceramics gradually decomposes， the number of mullite whiskers in cordierite porous ceramics increases significantly， and the material strength is greatly improved. When the sintering condition is 1 350℃×3 h， the molar ratio of cordierite/mullite in the prepared cordierite composite porous ceramics is about 6∶1. At this time， the material exhibits the best performance， with a porosity of 49. 16%， a bulk density of 1. 16 g/cm3， and a compressive strength of 12. 0 MPa. This research provides a new approach for the harmless treatment and resource utilization of secondary aluminum dross， as well as experimental evidence and technical references for preparing cordierite composite porous ceramics with high porosity and high strength.

Abstract:Beryllium resources in China are primarily occur in association with other minerals， exhibiting poor mineralogical characteristics and low utilization rates. China is rich in beryllium resources， but the resources primarily occur in association with other minerals with poor low grades， resulting in low utilization rates. The overall level of development and utilization remains low. As the market demand for beryllium continues to rise， the country is facing a shortage of beryllium supply. With growing scarcity of beryllium resources and rising prices， China faces an impending beryllium supply shortage of beryllium in the future. The main beryllium ore resources include beryl， phenacite and bertrandite， rare earth ore， chrysoberyl，etc. Beryl， the main source of beryllium production in China， is mostly processed using the traditional sulfuric acid method， which suffers from drawbacks such as long process flow， difficulty in lithium-beryllium separation， high beryllium loss， high energy consumption， and poor economic viability. Although the fluorination method offers advantages such as low energy consumption， less corrosion to equipment， and fewer impurities in the product， it is not suitable for ores with high calcium content. Other leaching processes of beryl include direct acid leaching and alkaline leaching. For bertrandite， the sulfuric acid-solvent extraction method is mainly used to separate beryllium and uranium， but it still requires a high-temperature smelting step； thus， researches focus on eliminating the smelting process through methods such as sulfuric acid curing leaching and high-pressure alkaline leaching with silica solidification. The extraction of beryllium from rare earth ores has poor universality and mostly adopts a “leaching first， separation later” approach. Chrysoberyl has high impurity content and stable crystal structure， and no effective method is currently available. Tailings of tungsten， uranium， fluorite， and other minerals often contain beryllium， which are typically leached with sulfuric acid. Beryllium extraction processes generate large amounts of waste such as fly ash and residue， which still contain high levels of beryllium， which can be directly leached by HF or NaOH. Currently， beryllium extraction processes in China face significant challenges， including misalignment between industrial capabilities and national strategic needs， complex procedures， and low recovery rates. There is an urgent need for coordinated efforts in policy guidance， basic research investment， extraction technology development， and resource expansion to achieve green and efficient development of Chinese beryllium resources.

Abstract:Laser cladding technology has demonstrated remarkable advantages in enhancing materials’ hightemperature resistance， corrosion resistance， wear resistance， and enabling material recycling. However， experimental observation of transient evolution processes within the molten pool remains challenging， which hinders in-depth understanding of microstructure formation mechanisms. Numerical simulation techniques have emerged as powerful tools to address this limitation. Thermophysical parameters， such as temperature gradients and cooling rates， play a critical regulatory role in determining grain geometric characteristics including size and morphology. Concurrently， hydrodynamic behaviors within the molten pool influence solute redistribution and preferred dendrite growth orientations， further shaping the microstructure. The non-equilibrium solidification process during laser cladding triggers competitive evolution of grain structures， with morphological evolution， size distribution， and crystallographic orientations being closely correlated with the anisotropic mechanical properties and functional characteristics of the coatings. Notably， topological morphology evolution at the dendrite growth front not only determines microscopic structural features like dislocation density and phase boundary characteristics but also exerts cross-scale effects on macroscopic service performance. This review systematically examines multiscale computational models in numerical simulations， elucidating the solidification dynamics during laser cladding processes. It particularly focuses on analyzing core issues such as coupled thermal-mass transport， grain topological structure evolution， non-equilibrium solute distribution， and dendrite morphology development， Future research in this field should place greater emphasis on refined multiphysics coupling， the integration of microstructural evolution with macroscopic performance， and the modeling of multicomponent alloy systems. Numerical simulation is expected to advance toward higher resolution， multidimensional characterization， and datadriven approaches， thereby providing stronger support for the development of high-performance coating materials and the optimization of processing parameters.

Abstract:Solid oxide fuel cell （SOFC） is considered as an important direction to promote the utilization of renewable energy， due to its advantages of clean operation， high efficiency and fuel flexibility. Biogas is a highquality anode fuel for SOFC because of its wide sources and abundant reserves. The SOFC anode acts as a critical component for fuel oxidation， electron transfer and ion conduction， which directly determines the electrochemical performance and long-term stability of the single cell. In this paper， the working principle， technical bottleneck and recent research breakthroughs of biogas SOFC anode were systematically reviewed， and carbon deposition， sulfur poisoning and interference of tar impurities were pointed out as the three major core challenges to improve performances of SOFC. In view of the above challenges， the current researches mainly focused on three major strategies： to enhance sulfur resistance and carbon deposition resistance through nickel （Ni）-based anodes and perovskite material modifications； to optimize fuel transport pathway by anode structure design； to inhibit side reactions by combining model-based theoretical calculations with experimental investigations through thermodynamic regulation （e. g. steam reforming） and kinetic study （e. g. alkali metal doping）. Future efforts should be devoted to advancing multiphysics coupling models， innovating poison-resistant anode materials， and establishing AI-powered adaptive control systems.

Abstract:Low-grade oxidized lead‐zinc ores are characterized by complex ore structure， low lead and zinc grades， high oxidation rate， high mud content， and fine particle size. The separation and enrichment of valuable metals via mineral processing technologies face challenges including high processing costs and low separation efficiency. Current literature on the processing of such ores still exhibits limitations such as small processing capacity and difficulty in meeting environmental protection requirements. This paper studied the comprehensive utilisation of a complex， low-grade， oxidized lead-zinc ore in Yunnan Province. The rotary kiln reduction process was used to investigate the impact of important smelting parameters， such as reaction temperature， coal ratio and reaction time， on the behaviour of volatile metals， such as lead， zinc， germanium and silver， during recovery. Combining FactSage thermodynamic calculations with XRD， SEM-EDS， ICP， and other analytical methods， the study revealed the phase evolution rules during the reduction process and the key mechanisms affecting metal volatilisation efficiency. Under the optimised conditions of 1 200℃ and a coal ratio of 20%， the zinc volatilisation rate reached 97. 40%， whereas the lead volatilisation rate was only 47. 87%. Germanium in the raw ore enters smoke dust via the reduction volatilisation process， whereas silver is primarily present in slag. Phase analysis indicates that， at high temperatures， the iron and lead sulfide phases are closely combined due to good wettability， which significantly inhibits the further volatilization of lead. Further exploration of the preoxidation-reduction volatilisation combined process could improve the recovery efficiency of lead and enhance the comprehensive utilisation level of such difficult-to-process resources.

Abstract:The properties of carbonaceous reductants have a significant influence on the product quality and production indicators of titanium slag smelting in electric furnaces. Semi-coke has advantages such as high fixed carbon content， strong reactivity， low ash content， and low sulfur content. However， there have been no literature reports on the use of semi-coke for titanium slag smelting. To investigate the effect of semi-coke on titanium slag smelting， this study compared and analyzed the gasification reactivity， thermogravimetric analysis， thermogravimetric analysis after mixing with ilmenite concentrate， and graphitization degree of semi-coke. A comparative analysis was also conducted between titanium slag smelting using pure coke breeze and that using a mixed reductant， leading to the following main conclusions. The analysis results show that the weight loss rate of semi-coke （89. 7%） is significantly higher than that of coke powder （44. 1%） at the same time， and the volatilization temperature of semi-coke and the graphitization degree is lower， indicating that the gasification reaction speed of semi-coke is faster and the reaction activity is higher， which is beneficial to accelerate the reduction process of titanium slag smelting. The industrial test results show that the content of TiO₂ in titanium slag is 74. 93% after using mixed reducing agent （ coke powder∶semi-coke = 8∶2， mass ratio）， which is slightly lower than the coke powder smelting index of 74. 96%， but the content of FeO in slag increases by 12. 28%， and the content of CaO， MgO， SiO₂ and Al₂O₃ decreases by 10. 76%. The average CO concentration of the gas produced by the mixed reducing agent smelting is increased by 2. 69%， the H₂ content is increased by 0. 51%， and the gas quality is steadily improved. The power consumption of smelting per ton of slag by mixed reducing agent is reduced by 25. 19 kWh/t， and the smelting cycle is shortened by 0. 61 h. Adding an appropriate amount of semi-coke to coke powder as a reducing agent for titanium slag smelting can improve the quality of titanium slag， shorten the smelting cycle and reduce the smelting cost. However， due to the faster gasification reaction speed and high reactivity， the internal gas discharge conditions of electric furnace should be optimized as far as possible to reduce the concentrated gas production. Considering the safety， semi-coke is more suitable for continuous charging smelting process.

Abstract:To address the problems of low grade of crude cobalt hydroxide and severe magnesium co-precipitation in the conventional magnesium oxide （MgO）-based wet cobalt precipitation process， an ammonium salt-MgO synergistic cobalt precipitation process was proposed in this study. By introducing ammonium salts such as ammonium sulfate， ammonium chloride， and ammonium bicarbonate， the cobalt precipitation efficiency was improved and impurity entrainment was suppressed. Using the iron-removal liquor from the hydrometallurgical treatment of copper-cobalt ores in the Democratic Republic of the Congo as the raw material， the effects of different ammonium salt types， ammonium sulfate concentration （0. 1-0. 3 mol/L）， and slurry-conditioning time （0-3 h） on cobalt precipitation rate， product grade， and residual magnesium ion content were systematically investigated. In addition， the synergistic mechanism of the ammonium salt-MgO system for cobalt precipitation was explored. The results showed that the ammonium sulfate-MgO synergistic system exhibited the best performance. Under the conditions of 0. 2 mol/L ammonium sulfate concentration，5% addition，0. 5 h slurry-conditioning time，25℃， and a stirring speed of 300 r/min， the cobalt grade of the product reached 52. 45%， while the magnesium ion content decreased to 1. 23%， representing a 78. 4% reduction compared with the conventional process， and meeting the first-grade standard （Co≥30%， Mg≤3%）. The role of ammonium sulfate in the MgO-based cobalt precipitation system can be attributed to two aspects. On the one hand， it suppresses excessive local alkalinity through dynamic pH buffering， thereby reducing the formation of magnesium hydroxide. On the other hand， it accelerates MgO hydration through interfacial activation， promotes the selective precipitation of cobalt ions， and inhibits magnesium co-precipitation. This process resolves the key problem of magnesium entrainment in the traditional MgO cobalt precipitation process， and provides an innovative solution for the efficient recovery of low-grade cobalt resources and the sustainable development of new energy materials， with significant economic and environmental benefits.

Abstract:Industrial primary ammonium rhenate is often accompanied by a variety of impurities. The traditional purification methods has the problems of low efficiency， high cost and strict equipment requirements. In this study， a crude ammonium rhenate product was used as the raw material， and its main impurities were copper， sulfur， selenium， iron， arsenic， etc. The high-purity ammonium rhenate was prepared by the multi-technology synergistic process of ‘pure water dissolution + ultrasonic assisted crystallization + hydrogen peroxide oxidation impurity removal + electrodialysis depth impurity removal’， and the process parameter optimization test and verification test were carried out. In the process of pure water dissolution， most of the copper sulfide and copper selenide impurities that are not easily soluble in water can be removed by filtration under the condition of stirring and dissolving at 85℃ for 1 h，because of ammonium rhenate easily dissolved in water at high temperature. Ultrasonic assisted crystallization process can improve the formation rate of crystal nucleus by the cavitation effect of ultrasonic wave， and it is difficult for impurity elements to adhere to the surface of the nucleus by its highfrequency vibration， and this process removes most of the arsenic and iron in the solution. Hydrogen peroxide oxidation impurity removal process can oxidize S^2- ， Se^2- ， Cu⁺ and other low valence impurity ions， so that it can produce high valence insoluble matter， and then filter to remove. The electrodialysis deep impurity removal process uses the ion exchange performance of the activated membrane to remove the potassium， sodium and other elements that are difficult to remove in the solution， as well as the residual copper and iron ions. In this process， crude ammonium rhenate with a grade of about 30% was used as raw material， and 5 N high-purity ammonium rhenate was successfully prepared which meeting the requirements of standard YS/T 894—2018. The process abandons the use of complex chemical agents， and the synergistic effect is significant， which greatly improves the impurity removal efficiency； and the process can stably and efficiently prepare high-purity ammonium rhenate products， which provide a new idea for the preparation of high-purity ammonium rhenate.

Abstract:The light sum method is one of the ideal ways to deal with high arsenic copper solution. The existing literature believes that the copper precipitation of arsenic sulfide slag is mainly the sulfide precipitation reaction of As₂S₃ with copper ions. However， the arsenic sulfide slag used in the field contains a large amount of As₂S₅ in addition to As₂S₃. In order to clarify the copper precipitation reaction mechanism of multivalent arsenic sulfide slag， this study used a high arsenic copper leaching solution and arsenic filter cake of an enterprise as raw materials to investigate the effect of factors such as arsenic sulfide dosage， reaction temperature and reaction time on the behavior of copper precipitation and arsenic leaching. The product was characterized and analyzed， and the following main conclusions were obtained. The amount of arsenic sulfide， reaction temperature and reaction time had a great influence on copper precipitation rate， arsenic leaching rate and arsenic content in slag. In general， with the increase of arsenic sulfide dosage， reaction temperature and reaction time， copper precipitation rate and arsenic leaching rate showed an upward trend， and arsenic content in slag showed a downward trend. Under the conditions of arsenic sulfide slag dosage 1. 3 times， reaction temperature 85℃ and reaction time 60 min， the copper deposition rate is more than 99%， and the arsenic content in the slag can reach 14. 64%. It is necessary to continue to extend the reaction time to soak arsenic. When the reaction time is extended to 255 min， the arsenic content in the slag is 4. 05%. The reaction process can be divided into copper precipitation stage and arsenic leaching stage. The copper precipitation stage （15-60 min） is dominated by the copper precipitation reaction of As₂S₃ and As₂S₅ and the copper precipitation reaction of As₂S₃ with sulfuric acid. The reaction kinetics is zero-order reaction， which is the control step of chemical reaction. In the arsenic leaching stage （75-255 min）， the conversion reaction of As₂S₅ to low valence arsenic sulfide and the sulfur generation reaction of As₂S₃ and As₂S₅ are the main reactions. The reaction kinetic model conforms to the Boltzmann model. In the later stage， the arsenic leaching rate changes little， and the arsenic content in the slag changes little. The results of this study complement the existing copper deposition mechanism of arsenic sulfide slag， that is， for multivalent arsenic sulfide slag with high As（V） content， in addition to As（III） participating in the copper deposition reaction， As（V） also participates in the copper deposition reaction， and there is a conversion to low valence arsenic sulfide to continue the copper deposition reaction.