The preparation of high purity ammonium paratungstate not only has important economic value,but also has great strategic significance.Reasonable control of molybdenum content in ammonium paratungstate and guarantee of product pass rate are the key to affect the development and economic benefits of enterprises.The effects of washing water pH value,washing temperature,washing time,liquid-solid ratio and washing frequency on the elution rates of molybdenum and tungsten were studied by single factor tests.The results show that the optimal conditions for molybdenum reduction from ammonium paratungstate by washing with pure water are washing water pH value of 7.0,reaction time of 20 min,reaction temperature of 65℃,liquid-solid ratio of 3∶1 and washing frequency of once.At this time,the elution rate of molybdenum reaches 82.01%,and the loss of tungsten is small with an elution rate of 3.97%.This method has the advantages of no other impurities,simple operation,environmentally friendly process and low production cost,and has certain reference value and significance for enterprise development and process improvement of ammonium paratungstate preparation.

The response surface method was used to investigate the molybdic acid precipitation process by adding sulfuric acid in the ammonium molybdate solution system,as the existing process suffers from low raw material utilization and poor quality and non-uniform particle size of the product.A optimizated quadratic polynomial regression model was established for the three process parameters of acid precipitation temperature A,initial MoO₃ concentration B,and end pH value of acid precipitation C and their interactions,with the molybdenum direct yield Y as the response value.Based on the one-factor experiments,the optimized regression model was obtained as Y=-125.19+5.96A+0.30B-9.80C+4.63×10^-4AB+0.92AC-0.07BC-0.048A²-1.87×10^-3B²-24.80C².The experimental results reveal that the molybdic acid precipitation process is controlled by multiple factors and sensitive to the response of individual factors with significant interactions.The order of influence significance of single factor is C>A>B,and the order of influence significance of interaction is AC>BC>AB.The optimized acid precipitation conditions are as follows:a stirring intensity of 450 r/min,a acid precipitation temperature of 72℃,an initial MoO₃ concentration of 70 g/L,an end pH value of 1.09 controlled by the back-addition method,and a heat preservation time of 180 min.Under the above conditions,the average molybdenum direct yield of 94.53%is achieved with a relative standard deviation of only 0.44%.The obtained molybdic acid is of high purity,good morphology,and relatively uniform particle size.

A optimal production practice study was conducted to address the issues of outdated equipment,high production costs and poor product quality consistency in the pilot production line of PrNd metal prepared by molten salt electrolysis method in a certain company.The results from the production practice show that by upgrading high-frequency switch power supply,modifying electrolytic wires,optimizing the design of electrolytic cells and controlling the quality of raw materials and product carbon content,the output of each furnace increases by 5.6%,the unit consumption decreases by 0.28%,the electricity consumption decreases by 18.6%,the first pass rate increases from 85%to 95%,and the consistency of product quality improves after optimization and upgrade.The optimal production practice can achieve the goal of reducing electri-city consumption and unit consumption and solving the problem of poor product quality consistency.

The process and reaction principle of lithium extraction from lepidolite were analyzed.Thermodynamic calculation,energy consumption comparison and phase diagram analysis were carried out for the two key steps of lithium extraction process from lepidolite,namely roasting energy saving and hydrometallurgical salt precipitation.The results show that the energy consumption of ordinary tunnel kilns is slightly lower than that of ordinary rotary kilns.Considering both investment and heat exchange efficiency,hot air combustion-assisted rotary kiln process with grate cooler is the best sulfate roasting process for lithium extraction from lepidolite.Pure mirabilite can be obtained by crystallization of purified leaching solution at 0℃.Na₂SO₄·3K₂SO₄ double salt can be obtained by evaporation crystallization at 15~50℃,and the precipitated Na₂SO₄·3K₂SO₄ at 25℃is the most.Only lithium-containing mixed salt can be obtained by evaporation crystallization at 100℃.

The thermodynamic calculation and simulation of direct carbothermal reduction of germanium dioxide for preparation of germanium metal and the verification experiments were carried out to explore the feasibility of short process preparation of germanium metal.Firstly,the standard Gibbs free energy change of each reaction in GeO₂-C and GeO₂-C-O₂ systems was calculated.Secondly,the multiphase simultaneous equilibrium of the two systems was simulated.Finally,the reduction experiment was carried out with pure germanium dioxide and carbon powder as raw materials in an inert atmosphere at 900℃.The results show that in the inert atmosphere,the increase of temperature is conducive to the carbothermal reduction of GeO₂ to produce GeO and Ge,and more carbon result in greater Ge yield.In the oxygen atmosphere,carbothermal reduction products of CeO₂ include GeO and Ge.However,oxygen preferentially reacts with carbon to produce CO₂,which is not conducive to the control of GeO₂ reduction process.The product of the reduction experiment is pure germanium metal with a direct recovery rate of 87.56%,which proves the feasibility of direct carbothermic reduction of germanium dioxide to prepare germanium metal.

GCr15 bearing steel with rare earth Y was prepared by vacuum arc melting method,and then heat treated with different process parameters.The phase,microstructure,Vickers hardness and frictional wear properties of the samples were characterized by X-ray diffractometer(XRD),scanning electron microscope(SEM),micro Vickers hardness tester and frictional wear tester.The results show that compared with GCr15 steel without rare earth Y,GCr15 steel with 0.036%Y has smaller grain size,greater lattice distortion,and more uniform carbide distribution.When the quenching temperature and holding time is 830℃and 20 min,and the tempering temperature and holding time is 160℃and 30 min,the GCr15-Y steel has the highest hardness of 814 HV and the smallest friction coefficient of 0.158.At this time,the furrow is shallow and narrow,the wear is the lightest,and the wear resistance is the best.The wear mechanism of GCr15-Y bearing steel under dry friction condition is mainly abrasive wear and adhesive wear.

In the production of high-quality regenerated brass alloys from scrap copper,Fe-rich phase segregates in the form of hard particles,affecting the machining performance of brass ingots.To improve the material yield ratio,La-B-Ti composite additive was used to improve the microstructure of brass ingots with high Fe content.By thermodynamic simulation and calculation,the effect of La-B-Ti on the microstructure of Cu-Zn-Pb-Fe system was analyzed,and the microstructure,hardness and electrical conductivity of brass ingots with different mass fractions of composite additive were experimentally investigated.The results show that La easily combines with Pb to form compounds,and Ti easily combines with Fe to form compounds.The composite additive can inhibit the aggregation and precipitation of Fe-rich phase and Pb phase,and refineαphase at the same time.In addition,La-B-Ti changes the number of grain boundaries and the morphology of precipitated phases in the Cu-Zn-Pb-Fe system.When the addition of the composite additive is 0.25%of the mass of high-Fe scrap copper,the regenerated brass ingot shows the highest hardness(181 HV)and relatively high electrical conductivity(11.85%IACS).This study provides a new idea to recover high-Fe scrap copper to regenerate brass ingots.

Nd₂Fe₁₄B/PrCo₅hybrid magnets were prepared by hot pressing and hot deformation with spark plasma sintering equipment,and their magnetic properties,microstructure and intergranular interaction were investigated.There are Nd₂Fe₁₄B and PrCo₅in both the hot-pressed and hot-deformed hybrid magnets.The anisotropy and magnetic properties of the hot-deformed magnets are significantly affected by the deformation amount.With the increase of the deformation amount,the anisotropy of the magnets increases,the grains are stretched into a lath shape along the direction perpendicular to the pressure,and the coercivity and maximum magnetic energy product decrease monotonously.At the same time,the intergranular exchange coupling of the magnets gradually weakens,and the long-range magnetostatic interaction strengthens.

A large-size niobium tube target was made by perforating and extruding of niobium ingot with a diameter of 300 mm,and then annealed at different temperatures.The recovery and recrystallization temperature of the niobium tube during annealing were determined by differential scanning calorimetry(DSC),and the texture evolution of niobium tube after extrusion and annealing was analyzed by electron backscattered diffraction(EBSD)technique.The results show that different annealing heating rates have little effect on the initial recrystallization temperature of niobium tube.The deformed microstructure of the extruded niobium tube is mainly<100>and<111>silk texture,and<110>predominant recrystallization texture is obtained after annealing.This study is helpful to improve the annealing process for the microstructure homogenization of extruded niobium tubes.

The effects of gradient extrusion on evolution of the grain orientation,grain size,and grain boundary orientation difference and mechanical properties of Ti₂AlNb-based alloy were studied by EBSD combined with microhardness test.The results show that preferred orientation<101>in the microstructure of Ti₂AlNb-based alloy gradually disappears after the gradient extrusion deformation,the grain size is gradiently distributed,and the structure of fine grains on the surface and coarse grains in the core is formed.The average grain size in the edge region decreases from the initial 20.64μm to 3.92μm,and the average grain size in the core region decreases to 11.24μm after gradient extrusion from two forming units.At the same time,the length of high-angle grain boundary in the edge region gradually increases from the initial 11166.5μm to 34905.8μm.The microhardness of the deformed sample shows an increasing gradient distribution from the core to the edge,and the average microhardness values of the first gradient and the second gradient increase by 9.9%and 11.5%respectively,compared with the initial sample.It provides theoretical support for the study of the large plastic deformation process of high temperature titanium alloy.