Aiming at the problems of high acid consumption,acidic gas escape and difficult treatment of radioactive slag in the treatment of mixed rare earth concentrates by high-temperature concentrated sulfuric acid roasting process,a low-temperature concentrated sulfuric acid roasting-water leaching process was developed.The effects of roasting time,roasting temperature,acid-mineral mass ratio and iron-phosphorus mass ratio on the leaching of various elements in the mixed rare earth concentrates were systematically studied.The results show that under the conditions of roasting time of 60 min,roasting temperature of 300℃,acid-mineral mass ratio of 2.0 and without adjusting iron-phosphorus mass ratio,the leaching rates of RE and Th reach 94.34%and 95.05%,respectively,and the formation of radioactive waste residue is significantly reduced.However,white precipitate is generated after the leaching solution stands,resulting in a decrease in the content of RE and Th in the leaching solution.By adding Fe₂O₃ to regulate iron-phospho-rus mass ratio in the roasting raw material to 3.0,the leaching rates of RE and Th are 94.80%and 71.20%,respectively,and the precipitation of rare earth pyrophosphate in the leaching solution is effectively inhibited.According to thermodynamic analysis,under low temperature conditions(≤300℃),the reactions between sulfuric acid and rare earth minerals proceed more readily,and the emission of SO₂ and SO₃ acidic gases can be suppressed.Compared with the high-temperature concentrated sulfuric acid roasting method,the low-temperature concentrated sulfuric acid roasting process combines environmental friendliness and resource efficiency,providing a way for the green extraction of mixed rare earth concentrates.

The effects of roasting process parameters such as concentrate particle size,roasting temperature,roasting time,and material layer thickness on the oxidation rate of roasted ore,praseodymium and neody-mium content in the cerium-rich concentrates,and leaching rate of rare earths,using Yakping bastnaesite concentrate as the raw material.The results indicate that employing smaller concentrate particle size,appropriate roasting temperature(500~525℃)and roasting time(3 h),and controlled material layer thickness(1.1 cm),could enhance the leaching rate of praseodymium and neodymium and reduce the praseodymium and neodymium content in the cerium-rich concentrates.However,due to the additional processing steps and energy consumption required for crushing concentrates,the original concentrate is directly roasted for easier industrial implementation.Under the above optimum conditions,the oxidation rate of roasted ore reaches 95.29%,the leaching rate of praseodymium and neodymium reaches 95.89%,and the praseodymium and neodymium content in the cerium-rich concentrates is minimized to 1.23%.This study provides a reference for achieving efficient praseodymium and neodymium leaching from bastnaesite.

A novel low-alkali sodiumization-reduction roasting process was proposed for refractory tantalum-niobium ores with high silicon and iron content.Thermodynamic analysis was conducted on the thermal decomposition and reduction reactions of the sodiumizing agent,the sodiumization reactions of tantalum,niobium,aluminum,and silicon,as well as the reduction reactions of iron,tantalum,and niobium oxides,to verify the feasibility of the process.The analysis results indicate that within the roasting tempe-rature range of 1264~1546 K,the addition of a sodiumizing agent and a reducing agent enables the reduction of the iron oxides in the tantalum-niobium ore to metallic Fe,which is subsequently removed by magnetic separation.Most of Si,Al,W,and Sb impurities can be converted into soluble salts,which are leached out by water and remain in the magnetic separation tailwater.In contrast,tantalum and niobium do not react with the sodiumizing agent or reducing agent and are enriched in the magnetic separation residue.This study provides a new approach for the clean and efficient smelting of tantalum and niobium.

The preparation process was optimized of high-purity niobium hydroxide from high-purity nio-bium solution(H₂NbF₇ solution)for niobium oxalate synthesis.The results demonstrate that under the optimal process conditions,including a feed solution concentration(Nb₂O₅ content)of 120 g/L,ammonia neutralization time of 5 h,blowing time of 16 h,drying temperature of 60℃,and drying time of 5 h,the prepared niobium hydroxide product exhibits excellent quality with a Nb₂O₅ content exceeding 73%and superior solubility in oxalic acid solution.In addition,the process operates stably.

Taking the weak acid leaching solution of secondary zinc oxide that is a by-product from the lead-zinc smelting system as the research subject,solvent extraction was employed to recover In,Ga,and Ge from it.The effects of solution pH value and the synergistic extractant YW100 on the extraction rates of In,Ga,and Ge were investigated through a series of extraction experiments.Suitable stripping agents and selective extraction separation processes for In,Ga and Ge were determined.The experimental results reveal that Fe³⁺significantly impacts the extraction of Ga and Ge,so it is necessary to reduce the Fe³⁺in the leaching solution before extraction.In the P204 extraction system,the extraction rate of In reaches 99.99%,while Ga and Ge are hardly extracted.The In-loaded organic phase is stripped with 6 mol/L hydrochloric acid,and the In stripping rate is close to 90%.Subsequently,the synergistic extraction system of P204+YW100 is used to extract Ga and Ge from the raffinate.The extraction rates of Ga and Ge reach 93.30%and 98.90%,respectively.The Ga-and Ge-loaded organic phase is first stripped with 6 mol/L sulfuric acid to recover Ga(achieving a stripping rate of 65%),followed by Ge stripping using sodium hypochlorite or ammonium fluoride solution,which yields a Ge stripping rate of approximately 90%.The selective extraction separation of In,Ga and Ge from the weak acid leaching solution of secondary zinc oxide have been realized,and the goal of efficient recycling and utilization of resources has been achieved.

To promote the recovery and utilization of aluminum and iron resources from red mud,the lea-ching behaviors of Al and Fe were studied in a dual-acid(H₂SO₄+HCl)system.The effects of dual-acid concentration,volume ratio of sulfuric acid to hydrochloric acid,leaching temperature,liquid-solid ratio,and leaching time on the leaching rates of Al and Fe were systematically investigated.The optimal leaching conditions are determined as follows:total volume fraction of sulfuric acid and hydrochloric acid of 28%,volume ratio of sulfuric acid to hydrochloric acid of 1∶1,leaching temperature of 100℃,liquid-solid ratio of 9 mL/g,and leaching time of 60 min.Under these conditions,the leaching rates of Al and Fe can reach 97.5%and 73.8%,respectively.The dual-acid leaching exhibits effective synergistic effect.Hydrochloric acid can form a stable complex with Fe³⁺,while sulfuric acid provides the necessary acidity and oxidizing ability to promote the dissolution of Al³⁺,which significantly enhances the leaching efficiency of aluminum and iron,and provides a novel approach for the resource utilization of red mud.

During the preparation of magnesium metal and its alloys by traditional molten salt electrolysis,the use of anhydrous MgCl₂ as the electrolytic raw material faces the problems of high dehydration cost and the generation of corrosive chlorine gas,while the direct use of MgO as the electrolytic raw material has been pursued in the field of magnesium metallurgy.Therefore,the system of Cu cathode|MgF₂-LiF-MgO molten salt|graphite anode was established to realize the direct preparation of Cu-Mg alloys by molten salt electrolysis,and the electrochemical behaviors of the ions in the molten salt system and the settling beha-vior of MgO in the molten salt were systematically investigated.The results show that during preparing Cu-Mg alloy by the molten salt electrolysis method,the cell voltage should be controlled within 1.5~4.5 V.Underpotential deposition of Mg²⁺occurs on the Cu cathode and O^2-is preferentially oxidized over F^-on the graphite electrode.The low solubility of MgO causes the molten salt after electrolysis to exhibit a stratified distribution state,namely,the bottom MgO settling layer,the middle MgO suspension diffusion layer,and the upper MgO-depleted layer.The depletion of MgO is likely to lead to the attenuation of the current intensity or the occurrence of an anode effect.Using Cu as the cathode,a Cu-Mg alloy with a Mg mass fraction of 19.98%is obtained after constant voltage electrolysis at 2.5 V for 11 A·h,and the current efficiency is 96.67%.The alloy product is mainly composed of Cu₂Mg phase and contains a small amount of CuMg₂ phase.

A series of Ag-xSc silver-based alloys were prepared using a vacuum medium-frequency induction melting furnace,followed by rolling and annealing.The metallographic microstructure of the alloy ingot was observed using an optical microscope(OM).For the annealed alloy,the phase composition was analyzed by a X-ray diffractometer(XRD),the electrical conductivity was measured using a conductivity meter,the hardness was tested by a micro-Vickers hardness tester,and potentiodynamic scanning was performed using an electrochemical workstation.Corrosion experiments were conducted in Na₂S solution and H₂S atmosphere,followed by analysis of the corrosion surface morphology and sulfur content using scanning electron microscope(SEM)coupled with energy-dispersive spectrometer(EDS).The results show that scandium in silver exists primarily in the form of the metallic compound Ag₄Sc,with a small amount of scandium atoms dissolved in the silver matrix.The addition of scandium can refine the silver grains.With the increase of scandium content,the electrical conductivity of the silver-based alloys gradually decreases,the hardness continuously increases,and the corrosion resistance first improves and then declines.The silver-based alloy with 0.75%(mass fraction)Sc exhibits the best corrosion resistance,with a self-corrosion current density of 676μA/cm² and a hardness of 114.4 HV_0.1.

High-strength aluminum alloy Al-9.0Zn-2.5Mg-2.2Cu-0.2Zr-xSc was designed,and its as-cast alloy was subjected to homogenizing annealing,hot rolling,solid solution and aging treatments.The reasons for adopting the two-stage homogenizing annealing and its effects on the microstructure of the as-cast alloy were analyzed,and the influence of the solid solution temperature on the microstructure and mechanical properties of the alloy,as well as the Sc content on the mechanical properties of the alloy,were also stu-died.The results show that the use of two-stage homogenizing annealing can not only eliminate the casting stress of the alloy and make the distribution of Zn,Mg and Cu elements more uniform,but also reduce the width of the grain boundary precipitate-free zone(PFZ),which is conducive to the improvement of alloy properties.As the solid solution temperature increases,the degree of recrystallization of the alloy sheet increases,and the number of residual second phases in the alloy decreases.Compared with other solid solution temperatures(450℃,460℃,480℃),the tensile strength of the alloy after solid solution treatment at 470℃for 2 h and aging treatment at 120℃for 24 h is the highest.With the increase of Sc content from 0 to 0.6%,the tensile strength of the alloy first increases and then decreases,and the elongation at break shows a decreasing trend.When the Sc content is 0.42%,the tensile strength of the alloy is the highest.

The influence of rare earth Ce on theα-Al grain size and eutectic Si morphology in the solidification microstructure,phase composition,and hardness of ZL114A aluminum alloy was investigated through a sand casting process simulation experiment.The results indicate that theα-Al grain size in the solidification microstructure of ZL114A aluminum alloy initially decreases and subsequently increases with the increase of the addition amount of rare earth Ce,while the Vickers hardness of the alloy exhibits an opposite trend of first increasing and then decreasing.The optimum mass fraction of rare earth Ce is 0.3%.Under this condition,the average grain sizes at the core and edge of the ingot decrease from the original 157μm and 143.2μm to 125.7μm and 122.6μm,respectively,corresponding to decreases of 19.9%and 14.4%.The morphology of eutectic Si transforms from the original lath shape to fine rod shape.Additionally,the addition of rare earth Ce promotes the preferred orientation growth of Al and Si atoms along the〈100〉and〈110〉directions.The Vickers hardness values at the core and edge of the ingot increase from the original 62.9 HV and 68.3 HV to 70.3 HV and 75.3 HV,respectively,corresponding to enhancements of 11.8%and 10.2%.