A scheelite ore in Henan was processed by soda pressure boiling leaching.In order to reduce the tungsten content in the leaching residue from original 4%to less than 0.5%,the effects of roasting time,sodium carbonate concentration,pressure leaching time and stirring speed on the loss rate of tungsten in the scheelite leaching residue were investigated.The results show that under the conditions of 40 min roasting time,160 g/L sodium carbonate concentration,120 min pressure leaching time,300 r/min stirring speed,205℃pressure leaching temperature and 5∶1 liquid-solid ratio,the tungsten content in the leaching residue is less than 0.15%,which basically minimizes the loss rate of tungsten in the leaching residue and can provide a valuable reference for the production of enterprises.

In view of the long-term tailing problem caused by residual ammonia nitrogen in ionic rare earth tailings in southern Jiangxi,indoor column leaching was carried out to simulate the environment of mining area,and then ammonium was removed by centralized leaching with leaching agents.Researches on lea-ching agent screening,leaching process optimization,leaching effect verification and residual leaching agent removal from tailings were carried out.The results show that magnesium sulfate is a suitable agent for the leaching of ammonia nitrogen from the ionic rare earth tailings in southern Jiangxi.When the concentration of magnesium sulfate solution reaches 2.5%(mass fraction),pH value is 5,and the injection strength is 0.3 mL/min,the leaching effect is relatively better,and the leaching rate of ammonia nitrogen from the tailings reaches 96.97%with the leaching liquid-solid ratio of 2.9.After the tailings leached by magnesium sulfate are immersed in the rainwater with pH value of 5.7 for 60 days,the concentration of ammonia nitrogen in the leachate is lower than the direct emission standard of 15 mg/L.Adding top water to the tai-lings after centralized leaching can leach down the residual magnesium ions in the tailings for recycling,which will not cause secondary pollution to the mining area of ionic rare earth tailings.

The existing niobium extraction processes of Bayan Obo rare earth-niobium-iron polymetallic ore are reviewed,including beneficiation process and metallurgy process,and the advantages and disadvantages of each process are also analyzed and discussed.The conventional beneficiation and metallurgy processes have never been able to solve the problem of efficient separation between niobium-bearing minerals and iron-bearing minerals with similar properties,so that high-grade niobium concentrates(or ferroniobium products)can’t be obtained.The new idea combining the methods of beneficiation and metallurgy,by actively changing the properties of raw materials and preferentially directionally converting multiple niobium-bearing minerals into niobium-bearing minerals with single and easily selectable properties,makes it possible to obtain high-grade niobium concentrates by subsequent beneficiation methods,which might be expected to solve the problem of efficient utilization of niobium resources in Bayan Obo.

The variation characteristics of particle size,morphology and micro-area composition of the key products of high-calcium vanadium slag in roasting stage were analyzed by scanning electron microscope and energy spectrometer.And the influence of heat preservation time on the roasting products of vanadium slag was studied.The results show that with the intension of heat preservation time,the particle size of iron oxide and pseudobrookite gradually increases;iron oxide gradually changes from regular granular crystal to irregular strip or bead-like crystal stock;pseudobrookite gradually changes from plate-like single crystal to irregular crystal stock;calcium-manganese vanadate gradually changes from dispergated form to locally aggregated form.As the heat preservation time increases,the overall change of the micro-area composition of iron oxide and pseudobrookite is relatively small,and calcium-manganese vanadate gradually changes from a mixed phase dominated by calcium vanadate to calcium vanadate with relatively high purity.

Taking lithium mica ore as the research object,the exploration experiments of sulfuric acid curing-water leaching,fluorinating acid leaching,calcium carbonate roasting-water leaching,calcium sulfate roasting-water leaching and chlorination roasting-water leaching were carried out.It is determined that the chlorination roasting-water leaching process at room temperature is more suitable for the comprehensive extraction of rubidium,cesium and lithium from lithium mica ore.Meanwhile,the effects of roasting temperature,roasting time,additive type and dosage,leaching liquid-to-solid ratio,and leaching temperature on the leaching rates of rubidium,cesium and lithium were also investigated.The results show that under the conditions of calcium chloride dosage of 50%,sodium carbonate dosage of 20%,roasting temperature of 750℃,roasting time of 6 h,and leaching liquid-to-solid ratio of 1∶1,more than 95%rubidium,94%cesium and 87%lithium could be leached after the process of chlorination roasting and water leaching at room temperature for 1 h.At the same time,sodium carbonate absorbs the chlorine gas released from calcium chloride during the roasting process,and the process has little environmental pollution.

The production of gallium concentrate from sulfuric acid leaching solution by P204+YW100 sy-nergistic extraction system in a domestic zinc smelter was introduced.Based on the analysis of the deficiencies in the process of extraction-stripping-sulfuration purification-neutralization hydrolysis precipitation,the following measures were put forward:stably control the acid content of the extraction solution at 10~20 g/L,reduce the iron ion concentration to below 0.2 g/L,and optimize the addition of synergist YW100 from intermittent supplementation to continuous supplementation.Diffusion dialysis was used to separate the free acid in the gallium stripping liquid.The source control of extraction was strengthened to reduce impurity elements entering the stripping solution.The sulfuration purification was canceled and sodium hydroxide was used as a neutralizing agent instead of sodium carbonate.The results show that after process optimization,the extraction of gallium increases from less than 75%to more than 99%.For treating high-acid gallium stripping solution by diffusion dialysis membrane,the retention rates of iron,copper,zinc,gallium,and sulfuric acid are 85.71%,87.27%,90.00%,90.54%and 9.71%,respectively.The recovery rate of acid reaches 90.29%,the recovered acid mixed with concentrated sulfuric acid can be used as the stripping agent of gallium,realizing the recycling of resources.The grade of gallium concentrate is improved from 8.51%to 26.47%,providing a high-quality material for the subsequent alkali dissolution-gallium electrowinning.

Surface oxidation is a major defect of drawn tungsten wire.Based on a comprehensive analysis of the formation rules and mechanisms of the surface oxidation of tungsten wire, this paper builds structural models and quality evaluation indexes of the tungsten wire surface layer, and correspondingly proposes improvement measures.The surface oxidation morphology of tungsten wire can be mainly divided into two types: surface grooves and graphite emulsion layer shedding, which are formed as a result of the non-uniformity and non-integrity of the surface carbon layer.To improve the surface quality of the tungsten wire, the key is to form a uniform and integral carbon layer and increase the effective carbon content of the surface layer.By controlling the granularity and viscosity of the graphite emulsion and setting the reasonable pass compression ratio, coating layers of the graphite emulsion, processing temperature and other processing parameters, it can effectively prevent the damage of the lubricating layer, build an ideal surface layer for the tungsten wire, and thus improve its surface quality.

Co_xW_yC composite powders were synthesized by in-situ carbonthermal reaction using Co₃O₄,WO₃and C as the raw powders with different carbon mass fraction(10.15%,11.47%,12.76%and 14.01%).And the influence law of carbon addition on the microstructure of Co_xW_yC composite powders was emphatically studied.The results show that the oxygen content of Co_xW_yC composite powders is less than 0.1%as the carbonization process is carried out after the completion of reduction.At the same time,the phase of Co_xW_yC composite powders is closely related to its carbon addition.When the carbon addition is 10.15%,the phase consists of W and Co₇W₆.When the carbon addition increases to 11.47%,the phase changes to Co₆W₆C.And when the carbon addition increases to 12.76%,Co₃W₃C phase and WC phase appear in the composite powders.When the carbon addition reaches 14.01%,the content of Co₃W₃C phase and WC phase both increases.In addition,there is mutual diffusion between tungsten and cobalt at high temperature during the in-situ carbonthermal reaction to form sintering neck,resulting in the dendritic morphology of Co_xW_yC composite powders.And the rapid diffusion of carbon forms a Co₆W₆C phase with low density,which causes the composite grains to expand and crack,improving the homogeneity of the particle size distribution of Co_xW_yC composite powders.When the carbon addition increases to 14.01%,fine WC grains are in-situ precipitated on the surface of the dendritic particles of the composite powders.

Nano WC-10 Co4 Cr coatings were prepared on ZG0 Cr13 Ni5 Mo stainless steel substrate by internal oxygen-propane high-velocity oxygen-fuel(HVOF)spraying,and the effects of spraying angle of 45°and 90°internal guns on the microstructure and performance of the coatings were studied.The phase composition and microstructure of the coatings prepared at different spraying angles were analyzed by X-ray diffractometer(XRD)and scanning electron microscope(SEM),and the microhardness and porosity of the coatings were measured by Vickers hardness tester and metalloscope.The surface roughness and 3 D morphology of the coatings were tested by roughometer and optical profilometer,and the sand abrasion resis-tance of the coating and the substrate was also comparatively studied by abrasion tester.The results show the main phases of the nano WC-10 Co4 Cr coatings prepared by 45°and 90°internal guns are WC,W₂C and amorphous CoCr alloy,and the small spraying angle easily results in stripy pore defects.The porosity of both groups of coatings increases with the decrease of spraying angle while the microhardness decreases with the decrease of spraying angle,and their hardness reaches the peak of 1313 HV_0.2 and 1383 HV_0.2 respectively at 90°spraying angle.The surface roughness of the coatings increases with the decrease of spraying angle,and the sand abrasion resistance of the coatings increases with the increase of spraying angle.When vertically sprayed,both groups of coatings get the highest abrasion resistance which is 7.12 times and 5.39 times of the substrate,respectively.The nano WC-10 Co4 Cr coating prepared by internal HVOF at the spraying angle above 40°could preserve good microstructure and performance,which proves the fact that the internal HVOF is suitable for the spraying strengthening in narrow internal space of workpiece.

The effect of Al₂O₃doping on the electrochemical corrosion resistance of molybdenum alloys in 3.5%NaCl solution was studied,and the corrosion mechanism of the alloys was analyzed.The results show that the corrosion resistance of Mo-Al₂O₃alloys is significantly better than that of pure molybdenum,and it increases at first and then decreases with the increase of Al₂O₃content.During the corrosion process,Cl^-is preferentially adsorbed on the defect positions of the molybdenum alloy oxide film to form pitting.With the increase of potential,the pitting expands along the grain boundary to become corrosion grooves.Al₂O₃can refine the molybdenum grains to promote the formation of a dense oxide film of molybdenum alloys which is less easily prone to pitting,thereby improving the corrosion resistance of the molybdenum alloys.However,when the volume fraction of Al₂O₃in molybdenum alloys reaches 1.6%,the Al₂O₃particles agglomerate and grow larger,which destroys the integrity of the oxide film of the molybdenum alloy and weakens their protection of the alloy matrix,resulting in a decrease in the corrosion resis-tance of the molybdenum alloy.