Study On Recovery Process Of Rare Earth Metals From Discarded Ndfeb Magnets

Rare earth metals,as a strategic resource,become the focus of recycling naturally under the background of recovering valuable metals from electronic waste.Rare earth materials are mostly used to produce a component called NdFeB magnet in electronic products,and the content of rare earth metals in NdFeB magnets is particularly high.Therefore,the recovery of rare earth metals from discarded NdFeB magnets is of great significance and has gradually become the focus of research by scientists all over the world.At present,hydrometallurgical process and pyrometallurgical process are the main methods to recover rare earth metals from discarded NdFeB magnets.Based on the analysis of the advantages and disadvantages of the existing pyrometallurgical process and pyrometallurgical process,this paper carries out innovative research on the shortcomings of the existing pyrometallurgical process and pyrometallurgical process.The main research contents and conclusions are as follows:（1）In order to prove that biochar can be used to recover rare earth metals,a kind of biochar was prepared from waste biomass as pyrometallurgical extractant.Rare earth metals in discarded NdFeB magnets were recovered by carbonization/hydrogenation-hydrolysis process.The transformation mechanism of rare earth metals in the recovery process was discussed by means of X-ray diffraction,scanning electron microscopy and energy spectrum analysis.The results show that rare earth elements in NdFeB magnets can react with carbon in biochar and hydrogen produced by further pyrolysis to form corresponding rare earth carbides and rare earth hydrides in the process of carbonization/hydrogenation.Rare earth carbides and rare earth hydrides can react with water to form rare earth hydroxides in the process of hydrolysis,thus realizing the efficient recovery of rare earth metals.（2）In order to obtain the optimum conditions for rare earth recovery,the effects of material placement mode,temperature and NdFeB powder layer thickness on rare earth recovery efficiency and purity of recycled products were optimized.The results show that under the current experimental conditions,the recovery efficiency of rare earth can reach 88.4%and the purity of rare earth hydroxides can reach 99.43%when the material is placed in powder layer form,the temperature is 1400℃and the thickness of NdFeB powder layer is 1mm.（3）In order to study the effect of ball milling activation method on the properties of samples,ball milling activation pretreatment was carried out at different rotational speeds by ball mill.And the samples before and after activation were characterized by particle size distribution,X-ray diffraction and scanning electron microscopy.The results showed that the ball milling activation method can reduce the particle size,increase the specific surface area and crystal structure defects of the samples by mechanical force,which can enhance the reactivity of the samples,thus promoting the leaching rate and leaching speed of rare earth metals in the leaching process.（4）In order to obtain the optimum leaching conditions of rare earth,the effects of ball milling speed,concentration of hydrochloric acid and solid-liquid ratio on the leaching efficiency of rare earth were studied.The results show that under the current experimental conditions,when the ball milling speed is 650 rpm,the concentration of hydrochloric acid is0.4 M and the solid-liquid ratio is 100 g L^-1,the leaching rate and leaching speed of rare earth are the best,and the use of hydrochloric acid is the least.Finally,the purity of rare earth oxides recovered can reach 99.9%.