The preparation methods,principle,actual production and research status of high-purity gold and silver are reviewed,and their preparation and application prospects are also discussed.

Cerium rich concentrate was employed as the raw material,dissolved in sulfuric acid and then separated by extraction with P204-kerosene.The raffinate was neutralized with MgO and then separated by extraction again with P204-kerosene,realizing tetravalent cerium separation from other trivalent rare earth and obtaining qualified cerium products and mixed rare earth chloride for the national standards.

The oxidation calcification roasting process of vanadium-chromium slag was theoretically analyzed based on the calculation of reaction Gibbs free energy.The results show that the formation of calcium vanadate has more thermodynamic advantages than the formation of calcium chromate during oxidation calcification roasting of vanadium-chromium slag.Vanadium can be preferentially extracted to achieve separation of V and Cr by controlling certain process conditions.Based on orthogonal experimental study of oxidation calcification roasting and acid leaching of vanadium-chromium slag,the effects were discussed of calcification time,oxidation time,calcium ratio and calcination temperature on the leaching rate of V and Cr.The results show that the influence factors of vanadium leaching rate have the following primary and secondary order：calcium ratio〉roasting temperature〉calcification time〉oxidation time.The effects of calcium ratio and roasting temperature on the leaching rate of V and Cr were investigated further by single factor experiments.The results show that the optimal leaching conditions for preferentially extracting vanadium are as follows：roasting temperature of 1 000℃,calcium ratio of 1.2,oxidation time of 2 hand calcification time of2 h.Under the optimal conditions,the leaching rates of vanadium and chromium are 85.76% and 14.61%,respectively.

The cathode materials（LiNi0.6Mn0.2Co0.2O2）in spent lithium ion batteries were processed by leaching with H2SO4 and reductants.The effects of H2SO4 concentration and leaching temperature on the leaching of valuable metals were studied.Optimal H2SO4 concentration and leaching temperature are determined of 2 mol/L and 40℃,respectively during leaching.Under the optimized conditions of H2SO4 concentration of 2 mol/L,the ratio of raw material to leaching agent of 100 g/L,leaching time of 2 h,leaching temperature of 40 ℃ and stirring speed of 500 r/min,the effects of such reductants as H2O2,C6H12O6 and Na2SO3 on the leaching of valuable metals were investigated by single factor experiments.The results show that the optimum addition of H2O2,C6H12O6 and Na2SO3 are 4.5%,80 g/L and 60 g/L,respectively.The effects of mixed reductants were also investigated by orthogonal experiments.When the composition of reductants is 120 g/L C6H12O6 and 100 g/L Na2SO3,the leaching rates of Co,Li,Mn and Ni are 93.51%,92.68%,95.61% and 92.93%,respectively,but the leaching rate of Al is only 18.57%.Compared with single reductant,mixed reductants with suitable composition can control the leaching of the impurity metal of Al under the condition that the leaching rate of valuable metals（Li、Ni、Mn、Co）is not obviously reduced.In addition,the factors affecting Al and Li leaching have the following primary and secondary orders：Na2SO3〉C6H12O6〉H2O2 and H2O2〉Na2SO3〉C6H12O6,respectively.And the factors affecting Co,Mn and Ni leaching have the following primary and secondary order：C6H12O6〉H2O2〉Na2SO3.

The latest research development of preparation and purification technology of trimethyl gallium is summarized,and the advantages and disadvantages of the existing technologies are analyzed.It is proposed that detailed enlarged study of the original technology is necessary during development of new technology,to further improve the economics of the existing synthesis preparation and separation purification techniques,and develop low-cost,safe and reliable preparation and purification methods of trimethyl gallium applicable to industrialization.

Ni4WxV（x=2,4,6）alloys were produced by vacuum induction melting,and 200μm thick alloy substrate tapes were fabricated by rolling assisted biaxial texture substrate tape technology.The magnetic properties and yield strength of the alloy substrate tapes were measured.By using X-ray diffraction（XRD）and electron backscattering diffraction（EBSD）,the cold rolling texture and recrystallization texture of the alloy substrate tapes with different composition were analyzed and compared with those of Ni5 Wsubstrate tape,to select the composition with better comprehensive performance.The results show that Ni4W2V alloy substrate tape has the best comprehensive performance with yield strength of 150.7 MPa,which is equivalent to Ni5 Walloy substrate tape.Ni4W2V alloy substrate tape has 55%saturation magnetization of Ni5 Wat room temperature,and its cube texture content is 56%（〈30°）.Therefore,Ni4W2V is a promising alloy composition.

The process technology was studied of mirror white molybdenum wire preparation by electrolytic polishing.Electrolytic method,electrolytic parameter,electrolytic medium,electrode material,and high temperature annealing were experimentally studied.The results show that mirror white molybdenum wire with surface roughness（Ra）of 0.2 can be produced by direct current electrolysis with direct contact between molybdenum wire and anode and using sulfuric acid electrolyte as the medium.Surface passivation and polishing of white molybdenum wire by high temperature annealing can not only improve surface oxidation resistance of white molybdenum wire,but also adjust its physical performance indexes.

The single alloy composition was designed by adding rare earth Ho to replace rare earth Dy,and the technology research scheme of melting,hydrogen decrepitation,jet mill grinding,seal press forming and low temperature sintering was employed.Finally,48 M（NdFeB380/107）sintered NdFeB permanent magnetic material with high magnetic energy product was producted at a low cost.The jet mill grinding is low pressure grinding to reduce the loss of Nd-rich phase and the particle size of the magnetic powder.

The corrosion of irregular sintered NdFeB magnets was researched with weight loss method in such solutions as distilled water,river water,sulfuric acid,potassium hydroxide solution and potassium chloride solution of different temperature and concentration.The specific surface area of the samples was estimated according to their shape,to calculate their corrosion rate under different conditions.The results show that the corrosion rate of the sample in the acid medium is relatively fast,and the corrosion rate increases with the increase of the acid solution concentration.However,alkali and salt solutions of low temperature and high concentration have relatively weak corrosivity to the samples.Distilled water has higher corrosivity to the samples than tap water.

Sintered（PrNd）29.8Tb1Dy0.2Cu0.5Al0.2Co1.5B0.99TixFe（x=00.8）magnets with different Ti content were prepared by intergranular alloying,and their microstructure,magnetic properties and mechanical properties were studied.The results show that the magnet grain can be effectively refined by adding Ti.The proper addition of Ti can improve intrinsic coercivity force and squareness of the magnets,but decrease the remanence and maximum magnetic energy product.Furthermore,Ti addition can decrease the bending strength of the magnets without no obvious effect on their hardness.