Rare Earth Recovery From NdFeB Magnet Scrap By The Oxidation Roasting-high Pressure Selective Leaching Method

The phase evolution during the oxidation roasting process of NdFeB powder at 800?was investigated.After 4^thh times of oxidation roasting,the weight gain rate was basically constant and the weight gain rate reached more than 99%of the theoretical weight gain rate.At present,the determination on the oxidation roasting stays at the stage on the study of the weight gain rate,and the research on the oxidation mechanism was lacked.The phase type and microstructural morphology was analyzed by X ray diffraction and scanning electron microscopy with energy spectrum.the oxidation mechanism of NdFeB powder was put forward under this temperature and the final formed phase was detected to NdBO₃,NdFeO₃ and Fe₂O₃.High pressure selective leaching experiment was carried out on the powder after complete oxidation roasting.The optimal temperature for the roasted NdFeB powder by high pressure leaching using hydrochloric acid were was 110?and the leaching time was30 min,and at this time the maximum leaching rate of rare earth was 96.27%.Then,the effects of hydrochloric acid dosage,hydrochloric acid concentration,powder particle size on the leaching rate of rare earth were discussed,and the maximum leaching rate of rare earth was 97.16%when hydrochloric acid dosage was 1.3 times of the theoretical value.However,when the amount of hydrochloric acid was 1.15 times and 1.3 times of the theoretical value,the improvement for the leaching rate of rare earth was not obvious.When hydrochloric acid concentration was 12.5%,the maximum leaching rate of rare earth was 96.71%.When hydrochloric acid concentration was 10.0%and 12.5%,it had little effect on rare earth leaching rate.When the particle size?D90?was less than 15.25?m,the maximum leaching rate of rare earth was 98.85%.The particle size of powder has little influence on the leaching rate of rare earth.The leaching reaction speed speeds up with the increase of the temperature,and thus the particle size of powder is no longer an important factor for affecting the leaching rate of rare earth.The leaching reaction of iron in Fe₂O₃and NdFeO₃ was determined.It is concluded that the leached iron was was derived from Fe₂O₃ and NdFeO₃.The advantage of selective pressure leaching process of oxidized NdFeB powder using hydrochloric acid was evaluated.The leaching Fe₂O₃ slag was further treated by direct reduction–slag/metal separation method,and the optimal reduction condition of Fe₂O₃ slag was determined to be 95%under the condition of 1025?for 75 min.Fe-Co alloy was obtained through slag/metal separation experiment.According to the data obtained from chemical composition analysis of samples,the content of rare earth oxide in the separated slag reached 36.6%and the recovery rate of cobalt was 74.16%.The secondary utilization of NdFeB waste was completed.