The process of deep chromium removal from Na2WO4 solution by reductive hydrolysis-magnesium salt coprecipitation was studied,and the separation of tungsten from chromium in chromium magnesium slag was realized by once alkali leaching.The results show that after adding 3 times the theoretical amount of Na2S at 70℃,controlling the pH value at 8~9 for 0.5 h,adding 1%MgSO4 solution to continue the reaction for 0.5 h,and then filtrating,the ratio of Cr content to WO3 content in the filtrate is less than 1.6×10^-4.When the final alkalinity of chromium magnesium slag leaching is controlled at 30~40 g/L,WO3 recovery is more than 96%,and the ratio of Cr content to WO3 content in the leaching solution is less than 1.6×10^-4.

Tungsten powder with excessive iron content will be produced during the reduction of tungsten oxide in iron vessel,which cannot be used for subsequent product preparation and is treated as waste.Therefore,acid leaching process was used to purify the tungsten powder containing iron,and dissolve the iron in the tungsten powder to the maximum extent.Firstly,in the hydrochloric acid system,the influence of hydrochloric acid concentration,leaching temperature,leaching time and liquid-solid ratio on the effect of iron removal by acid leaching was investigated by using the variable control method.The iron removal rate is only 84.98%under the optimal conditions of hydrochloric acid concentration 45 g/L,leaching temperature 80℃,leaching time 4 h and liquid-solid ratio 9∶1.Then,the influence of acid type,oxidant amount and acid leaching times on iron leaching was further studied.The comprehensive optimization leaching conditions are as follows:two-stage leaching of H3PO4-H2SO4 mixed acid(volume ratio 1∶4),acid concentration 45 g/L and leaching time 4 h.The metal powder with the lowest iron content of 0.016% is obtained.Under the optimized conditions,the iron removal rate is 99.27% in the 10-kg expansion test,which meets the purity requirement of commercial tungsten powder.

With waste rare earth phosphor as the raw material after aluminum removal by acid leaching,caustic soda sintering and water washing,two-stage acid leaching and orthogonal experiment were used to optimize acid leaching conditions.The results show that the influence order of each factor on rare earth leaching in the first stage is as follows:liquid-solid ratio>HCl concentration>leaching time>leaching temperature>H2O2 dosage.Under the optimal conditions of solid-liquid Ratio of 6∶1,HCl concentration of 6 mol/L,leaching time of 60 min,leaching temperature of 60℃,and H2O2 dosage of 8%(volume fraction),the total rare earth leaching rate reaches 95.48%and the residual acid concentration is 2.18 mol/L,the concentration of Al impurity is up to 134 mmol/L,and Fe and Si are 1.78 mmol/L and 3.89 mmol/L,respectively.In the second stage,when the leaching temperature and time are 60℃and 60 min,and the pH value of the leaching solution is adjusted to 4 by adding fresh dealuminated slag,the concentration of Al,Fe and Si impurities in leaching solution is reduced to 24.1 mmol/L,<0.09 mmol/L and 3.89 mmol/L,meeting the requirements of subsequent extraction.

The direct reduction process was used to treat crude concentrate from benefication of V-Ti-Fe polymetallic ore.The contents of TFe,TiO2 and V2O5 in the crude concentrate are 48.57%,15.69%and 0.76%,respectively.The metal iron powder(92.13%TFe content,95.45%Fe recovery)and vanadium-rich titanium material(44.07%TiO2 content,2.01%V2O5 content,87.77%Ti recovery,82.79%V recovery)can be obtained under these conditions:The additive is 15%sodium sulfate and 1.5%borax,the reducing agent is HY-bituminous coal,the reduction temperature is 1150℃,the reduction time is 90 min,the grinding fineness is 77.5%mineral grains with particle size less than 0.074 mm,and the magnetic field intensity is 120 mT.The vanadium-rich titanium material can be metallurgically extracted to recover V and Ti,which provides a feasible technical route for the comprehensive utilization of such resources.

Using two kinds of molybdenum powders with different physical properties as raw materials,pure Mo plates with a thickness of 1.8 mm and a total deformation of 90%were prepared by cold isostatic pressing,intermediate frequency induction sintering and cross rolling.The effect of Mo powder quality on microstructure and mechanical properties of pure Mo plates was studied.The results show that the pure molybdenum plates prepared by molybdenum powders with low degree of agglomeration,good dispersion and relatively uniform particle size have better microstructure,density,hardness,tensile strength and elongation than those prepared by molybdenum powders with non-uniform particle size and agglomeration.

The catalytic denitrification performance of Bayan Obo rare earth tailings was studied.The results show that the rare earth tailings have good catalytic denitration performance.With the increase of reaction temperature and carbon to nitrogen ratio,denitration efficiency of the tailings obviously increases.When carbon to nitrogen ratio is 4∶1 and temperature is 900 ℃,NO conversion rate with catalysis of un-calcined tailings reaches 97%.Fe element in the rare earth tailings exists mainly in the form of Fe2O3 and Fe3O4,and Fe element changes to a low-valent state during CO reduction of NO catalyzed by the tailings.The increase of Fe-containing substances and the synergistic effect of various substances can enhance the catalytic denitration activity of the tailings.The natural tailings contain a large amount of Ce^3+,and the amount further increases in CO reducing atmosphere to improve denitrification ability of the tailings.Temperature-programmed reduction experimental results show that the tailings have excellent reducing ability.

Different contents of rare earth Ce was added to 3003 aluminum alloy,and the effect of Ce on the microstructure and properties of aluminum alloy was studied.The microstructure of the alloy was analyzed by SEM and EDS,and Vickers hardness of the alloy was tested.The results show that the strip-like tissue in 3003 aluminum alloy is Al4Mn,distributed in the black Al matrix.With the increase of Ce content,the grains of the alloy are remarkably refined,a small amount of needle-like,flaky or granular white tissue Al3Ce is precipitated,and the microhardness of the alloy gradually increases.When the Ce content in the alloy is 0.35%,solid solution in the alloy is saturated,and therefore the optimal Ce content in 3003 aluminum alloy is 0.35%.

ZL205 A alloy specimens containing 0.1%Sc were prepared by sand casting and water-cooled metal casting,respectively.The effects of casting methods on microstructure and mechanical properties of the alloys were studied by means of mechanical property test,SEM,EDS and TEM.The results show that the formation of brittle W(Al8-xCu4+xSc)phase can be inhibited by increasing cooling rate in water-cooled metal mold.After T6 treatment,the size of precipitated phases of the alloy casted in water-cooled metal mold is slightly larger and the amount of precipitated phases increases.T6 tensile strength of ZL205 A alloys casted in sand mold and water-cooled metal mold is 447.8 MPa and 474.64 MPa,and their elongation is 1.60%and 10.52%,respectively.The elongation of the alloy is significantly increased by water-cooled metal mold casting.

Ti/HA gradient composites were prepared by centrifugation-gelcasting technology.The effects of solid contents and Ti contents on viscosity of Ti/HA slurries were studied.The effects of initiator and catalyst contents on initial solidification time of the slurries were analyzed.The density was measured of different segments of green Ti/HA composites prepared with different centrifugal rotation speed and time and slurry solid contents,in order to study the mass separation phenomenon of Ti and HA particles during centrifugal forming.The microstructure of different segments of sintered compacts was observed by SEM,and their bending strength and fracture toughness were measured.Ti/HA slurry with 50% solid and 7% Ti has viscosity of 232.1 mPa·s.With 1.2% initiator and 0.9% catalyst,the initial solidification time of Ti/HA slurry is 10 min.When the above slurry is centrifuged at 1000 r/min for 10 min,the green compact has good density gradient.When the above green compact is sintered at 1000℃ for 2h,the obtained Ti/HA composite has good gradient distribution of Ti particles,and its bending strength and fracture toughness are 82.2 MPa and 1.71 MPa·m^1/2,increased by 153% and 116% over pure HA material.

Using titanium dioxide(TiO2)and zinc oxide(ZnO)powders as precursors,the TiO2-ZnO composite powders with different ZnO molar fraction(x)were synthesized via the solid phase method.The structure,morphology and properties of the composite materials were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM)and ultraviolet-visible(UV-Vis)absorption spectrometer,respectively.The effects of different ZnO molar fraction and calcination temperature on the structure and morphology of TiO2-ZnO composites were investigated,and the photocatalytic activity of the composites for degradation of methyl orange was also studied.The results show that the calcination temperature has a great influence on the structure and morphology of the composites.With t=600℃ and x=0.440,the TiO2-ZnO powder is composed of wurtzite ZnO,anatase TiO2 and a small amount of Ti3Zn3O0.5,and the interface particles are closely contacted.The combination of ZnO and TiO2 not only enhances the absorption of the composites in the ultraviolet region,but also enhances the absorption in the visible region.In addition,the TiO2-ZnO composite(x=0.440)exhibits good photocatalytic activity for organic dye methyl orange,and the degradation rate of methyl orange reaches 95.7% after UV irradiation for 120 min.