Rare earth molten salt electrolytic slag is a rare-earth-based solid waste generated during the preparation of rare earth metals and their alloys by molten salt electrolysis,containing abundant rare earth metals,fluorine,and lithium resources.This paper reviews the present situation of valuable metal recovery and reuse from rare earth molten salt electrolytic slag,and introduces the technical advantages and problems of physical,acid,and alkali processes.The paper also focuses on the existing issues and future development trends of industrialized technologies of concentrated sulfuric acid roasting and sodium hydroxide roasting,hoping to provide reference for resource recycling of rare earth molten salt electrolytic slag.

In view of the characteristics and actuality of unbalanced utilization of Bayan Obo niobium concentrate,the electromagnetic action is introduced to realize the dual objectives of efficient separation of metallic iron resources and comprehensive utilization of niobium carbide in Bayan Obo niobium concentrate.In this research,the effect of electromagnetic action on the melting and separation of the niobium concentrate was studied by using self-designed electromagnetic melting and separation device.The results indicate that the electromagnetic action can promote the separation of slag and iron after the reduction of niobium concentrate to reduce the residual iron in the slag.When the current frequency is fixed,the yield of metallic iron increases significantly with the increase of the current intensity.When the current intensity is fixed,the iron yield decreases with the increase of the current frequency.The electromagnetic action promotes the contact between niobium carbide and iron.Under the same current frequency,the content of niobium carbide in iron increases significantly with the increase of the current intensity,while it decreases obviously with the increase of the current frequency under the same current intensity.The magnetic field produced by low frequency and high intensity current can improve the dispersion effect of niobium carbide in iron phase,and the niobium carbide particles in iron are obviously dispersed.

WC-Al₂O₃composite was prepared by vacuum hot-pressing sintering method.The corrosion behavior of the WC-Al₂O₃composite in NaCl solution with different concentrations was studied by electrochemical corrosion method,the open circuit potential,polarization curve and impedance spectrum were mainly mea-sured,and the corrosion surface of the sample was characterized by SEM and XPS.The results show that the corrosion mechanism of the WC-Al₂O₃composite in NaCl solution is the oxidation of WC phase and the dissolution of Al₂O₃phase.With the increase of NaCl solution concentration,the corrosion current density decreases from 19.2μA/cm²to 7.5μA/cm²,while the total impedance increases from 178702·cm²to 215342·cm²,gradually improving the corrosion resistance of WC-Al₂O₃.When the NaCl solution concentration is high,the decrease of dissolved oxygen content in the solution becomes the main factor to control the electrochemical corrosion.The low dissolved oxygen content inhibits the electrochemical reaction process of the cathode,thereby inhibiting the overall electrochemical corrosion rate.

Due to its excellent physicochemical properties of high strength at high temperature,good corrosion resistance,and strong radiation resistance,molybdenum coating has promising application prospects in metallurgy,aerospace,and nuclear industry.This paper reviews the main preparation methods of the molybdenum coating,including thermal spraying,physical vapor deposition and electrodeposition,and compares the advantages and disadvantages of different methods.In addition,the research status of the electrodeposition of the molybdenum coating in molten salt and aqueous solution is emphasized.The comparisons of the effects of active salt,support electrolyte,and additives on molten salt electrodeposition and molybdenum coating quality are also conducted.At present,the molybdenum coating prepared in molybdate-fluoride-oxide molten salt system has the best comprehensive performance.Aqueous solution electrodeposition has low preparation temperature and wide applicability,but it faces the difficulty of restraining hydrogen evolution and the problem of MoO₄^2-being sensitive to pH value,resulting in weak bonding between the molybdenum coating and the interface.

The effects of the combined addition of Sc and Zr on the microstructure and mechanical properties of ZL114A alloy were studied by polarized light microscope,DSC,SEM and Vickers hardness tester.The results show that for ZLll4A alloy with Al-Ti-B grain refinement,the nucleation temperature of primaryα-Al grains increases from 619.2 C to 621.6 C after the combined addition of Sc and Zr,and the number of nucleation cores also increases.The nucleation ofα-Al grains becomes easier and the grains are further refined,of which the size decreases by 9.8%from 319.2μm to 287.8μm.The combined addition of Sc and Zr has little effect on the eutectic Si of ZLll4A alloy,indicating that the change in mechanical properties of ZLl14A+Sc+Zr alloy is mainly attributed to the change in the size of primaryα-Al grains.After the combined addition of Sc and Zr,the hardness of ZL1l4A alloy increases due to grain refinement.

GCrl5 bearing steel with different Y contents was prepared by vacuum induction furnace,and the effects of rare earth Y on the fatigue and wear resistance of the GCrl5 bearing steel were investigated by bending fatigue test and sliding wear test.The results show that the fatigue life of the test steel significantly increases with the addition of the rare earth Y.The fatigue fracture morphology of the test steel without Y addition is mainly fluvial and slightly dimpled,and the fracture mode is brittle fracture.The fatigue fracture of the test steel added with a small amount of Y exhibits fatigue striations,and its width decreases with the increase of rare earth Y.In addition,the fatigue fracture inclusions of the test steel without Y addition are MnS-Al₂O₃ composite inclusions with irregular angles,which are modified into spherical Al-O-Y-Mn-S rare earth inclusions with the addition of a small amount of Y,thereby improving the fatigue performance of the test steel.With the increase of rare earth Y,the wear loss of the test steel gradually decreases,its friction coefficient gradually decreases as well,and the wear resistance is enhanced.The wear mechanism of the test steel is a joint action of abrasive wear and fatigue wear,and with the increase of rare earth Y,the abrasive wear and fatigue wear gradually reduce.

Bayan Obo rare earth tailings are composed of hematite,bastnasite,fluorite,quartz and magnetite,in which rare earth element Ce and transition metals Fe,Mn are the active elements required for catalyst.In this paper,activated rare earth tailings were modified by Ce using impregnation method,and the effects of Ce modification on the performance of activated rare earth tailings catalyst were investigated by SEM-EDS,XRD,BET,NH₃-TPD,H₂-TPR and XPS.The results show that the Ce-modified activated rare earth tailings catalyst is dominated by mesoporous structure and Ce element is highly dispersed on the catalyst surface.There is a synergistic effect between Ce and Fe,and the existence of a redox couple between them promotes the transformation between different valence states of Ce and Fe ions,enhances the redox ability of the catalyst and increases the number of acid sites,which provides favorable environment for the adsorption and activation of NH₃,improving the denitration efficiency of the catalyst.After being modified by 15%Ce,the denitration efficiency of the activated rare earth tailings increases from 70%to 82%,the N₂selectivity is above 90%,and the reaction temperature window is widened to 275~450℃.

The properties of rolling-modified Pb-Ag-Ca-Sr-RE anode were studied.The effects of rolling direction,deformation and temperature on the anode resistivity were investigated,as well as the anode potential,cell voltage,current efficiency,energy consumption,corrosion rate and hardness under different crossrolling deformation.The results show that compared with the rolling temperature,the rolling direction and deformation have a greater impact on the anode resistivity.The anode modified by cross rolling under the conditions of rolling deformation of 60%and rolling temperature of 35℃has the best comprehensive properties:stable anode potential of 1.296 V,cell voltage of 3.08 V,current efficiency of 91.1%,electrolytic energy consumption for producing zinc of 2771.43 kW.h/t,corrosion rate of 4.8 g/(m².h),and hardness of 35.4 HV.

Using Bayan Obo iron concentrate and Al₂O₃powder as the main raw materials,Fe and FeAl₂O₄were generated in situ by controllable carbothermal reduction of iron concentrate and sintered at high temperature under normal pressure to prepare Fe/FeAl₂O₄cermet.The effects of Nb₂O₅,content on the properties and microstructure of the cermet were discussed.The results show that the two phases in the prepared cermet are uniformly distributed.The addition of Nb₂O₅can both activate the surface/interface of the cermet particles to facilitate sintering and promote the formation of columnar micro-nano crystals in the ceramic phase.When the content of Nb₂O₅,is 2%,the mechanical properties can be significantly improved,and the Vickers hardness and bending strength of the cermet under the optimized conditions reach 596 MPa and 132 MPa,respectively.At this time,the fracture of the cermet belongs to ductile fracture.The research can provide a process route for the low-cost preparation of cermet and fully utilize the unique key strategic element niobium resources of Bayan Obo mine.

Selective laser melting(SLM)was used as the forming process of high temperature titanium alloy,and the influence of heat treatment temperature on the microstructure and mechanical properties of the SLM-formed high temperature titanium alloy was studied.The experimental results show that with the increase of input laser energy,the defects inside the formed alloy change from irregular unfused defects to regular spherical hole defects.The optimal forming process parameters include laser power of 190 W,scanning speed of 560 mm/s,powder layer thickness of 0.03 mm,and scanning spacing of 0.06 mm.When the heat treatment temperature is lower than the phase transformation temperature,the alloy exhibits basketweave microstructure composed of lathαandβresidual microstructure.In addition,the content of the lathαin the alloy microstructure decreases with the increase of temperature,its length-width ratio decreases,and part of the lath a gradually spheroidizes.When the heat treatment temperature is higher than the phase transformation temperature,the basketweave microstructure in the alloy is transformed into Widmanstatten microstructure.With the increase of heat treatment temperature,the tensile strength of the alloy is basically unchanged,the yield strength is increased,and the plasticity shows a trend of decreasing at first and then increasing.The best strength-plasticity matching of the alloy is achieved under the heat treatment conditions of 995℃×2 h/AC:the tensile strength is 972 MPa,the yield strength is 774.5 MPa,and the elongation is 16%.