Study On Recovery Of Rare Earth Elements From NdFeB Waste By Sulfation Roasting

NdFeB permanent magnet materials are developing rapidly because of their excellent magnetic properties.Therefore,the demand for rare earth resources is increasing,among which Nd,Pr,Dy,Tb and other valuable rare earth elements are consumed in large quantities,resulting in the unbalanced utilization of rare earth resources.And waste materials are produced in every process of NdFeB production,the total amount of waste is about 30%.In order to realize the sustainable development of rare earth permanent magnet industry,the recovery of rare earth elements from NdFeB waste has become a research hotspot in recent years.In this paper,rare earth elements in NdFeB waste were selectively recovered by oxidation roasting-selective sulfation roasting-water leaching method.The results were as follows:NdFeB waste materials were oxidized and roasted in H₂O_(g)-O₂,O₂ and air atmosphere,and its oxidation efficiency was analyzed by the weight gain rate of the product.The results showed that the theoretical weight gain rate of NdFeB waste could be achieved by roasting at 850?for 3h in H₂O_(g)-O₂ atmosphere,and the oxidation rate was the fastest.XRD and SEM were used to analyze and discuss the phase evolution and microscopic morphology of NdFeB waste at various stages.The results showed that the complete oxidation material was composed of Fe₂O₃,NdFeO₃and NdBO₃phases;The oxidation mechanism was that Fe diffuses from inside to outside and O element diffuses from outside to inside.The feasibility of sulfation of Nd₂O₃,NdFeO₃ and NdBO₃ with ferric sulfate was studied,and the effects of roasting temperature and the amount of ferric sulfate on rare earth leaching rate were explored.The results showed that the leaching rate of rare earth was 96.9%when the optimum roasting temperature was 700?and the amount of ferric sulfate was 1.5 times of the theoretical amount for reaction of Nd₂O₃ with ferric sulfate.For reaction of NdFeO₃ withferric sulfate,when the amount of ferric sulfate was 1.8 times of the theoretical amount at 700?,the leaching rate of rare earth reached 96.7%.For reaction of NdBO₃ withferric sulfate,the leaching rate of rare earth was 73.2%when the amount of ferric sulfate was 1.7 times of the theoretical amount at 700?.In this paper,two methods were used to sulfate NdFeB oxide.Firstly,the selective sulfation roasting of ferric sulfate and NdFeB oxide was carried out to explore the influence of waste particle size on rare earth leaching rate.The results showed that with the decrease of D₉₀ from 16.412?m to 4.412?m,the leaching rate of rare earth could be increased from 21.2%to 77.7%,and D₉₀ continued to decrease to 4.191?m.The leaching rate of rare earth could be increased to 82.43%.Secondly,the reduction of sulfuric acid and neodymium iron boron oxide material sulfuric acid roasting,to explore the effect of sulfuric acid dosage on rare earth leaching rate.The results showed that the leaching rate of rare earth could reach 91.74%when 98%concentrated sulfuric acid 2.25 times of the theoretical amount was used to prepare 50%sulfuric acid solution,which was then sulfated and roasted with NdFeB oxide at low temperature 80?,medium temperature 300?and high temperature 700?.XRD and SEM were used to analyze the sulfated calciner and water leaching material at low temperature,medium temperature and high temperature.The results showed that the sulfuric acid and rare earth were sulfated selectively at medium temperature of 300?;At 700?,the selective sulfation of ferric sulfate and rare earth was completed,and the rare earth was converted into rare earth sulfate.The efficient recovery of rare earth was realized.