Study On The Recovery Process Of Rare Earth From NdFeB Sludge

The increasing application of rare earth elements(REEs)and the gradual scarcity of rare earth resources make it particularly important to recover REEs from secondary resources.NdFeB magnets are the most widely used field of rare earth resources in modern times.During its production process,a large amount of cutting waste will be generated,which is rich in REEs and iron elements;Therefore,it is of great significance to study the recycling of NdFeB sludge.In this paper,two processes of phosphoric acid selective leaching and phosphoric acid complete leaching were put forward to recover REEs and iron from NdFeB sludge,and two methods of preparing rare earth oxalate by rare earth intermediate product was studied.In the phosphoric acid selective leaching process,98.91% of the REEs in the waste were recovered in one step to form REEPO4·n H2 O precipitate under the conditions of phosphoric acid concentration of 4 mol/L,temperature of 80 ?,liquid-solid ratio of30:1 m L/g and the time of 90 min,while 98.76% of the iron elements in the waste were leached into the solution.It can be found that the selective leaching process of phosphoric acid can effectively recover REEs and separate from iron in one step.But the REEPO4·n H2 O precipitation contains iron impurities and stone slag,which can be completely dissolved in HCl concentration of 4 mol/L,temperature of 40 ?,liquid-solid ratio of 20:1 m L/g and a time of 20 min,and the REEs in the solution can be completely precipitated and recovered when the amount of oxalic acid is 1.5 times of stoichiometry,temperature of 80 ? and p H=1.5.In the phosphoric acid complete leaching process,99.16% of iron and 99.33% of REEs were leached into the solution under the conditions of H3PO4 concentration of 7mol/L,temperature of 25 ?,liquid-solid ratio of 20:1 m L/g and time of 40 min.After the leaching solution was heated at 90 ? for 2 h,the rare earth phosphate precipitate with little impurity was obtained,which can effectively separated from the iron element in the solution.Under the conditions of oxalic acid concentration of 40 g/L,temperature of 25 ?,liquid-solid ratio of 20:1 m L/g and time of 50 min,the rare earth phosphate precipitate can be completely transformed into rare earth oxalate phase.This not only simplifies the preparation process of rare earth oxalate,but also saves the chemical reagents.After separation and recovery of the REEs,oxalic acid was used to recover iron from phosphoric acid leaching solution.91.23% of the iron in the solution was recovered when the amount of oxalic acid was 2 times of stoichiometry,the temperature was 25 ? and the time was 90 min.In the process of recovering iron,phosphoric acid is regenerated,but the residual C₂O₄^2- in the regenerated phosphoric acid can not be directly reused.It can be completely removed by reacting at 25 ? for3 h with excess iron powder,so that the regenerated phosphoric acid can be reused in the leaching of NdFeB sludge.