Magnetic property recovery in Nd-Fe-B bonded magnet wastes with chemical reaction and physical dissolution

Abstract

The main difficulty for the recovery of Nd-Fe-B bonded magnet wastes is how to completely remove the epoxy resins. In this study, chemical reaction and physical dissolution were combined to remove the epoxy resins by adding ammonia-water and mixed organic solvents. Ammonia-water can react with the epoxy functional group of epoxy resin to generate polyols. Mixed organic solvents of alcohol, dimethyl formamide (DMF), and tetrahydrofuran (THF) can dissolve the generated polyols and residual epoxy resins. Under the optimum processing conditions, the epoxy resins in the waste magnetic powders are substantially removed. The oxygen and carbon contents in the recycled magnetic powder are reduced from 13500 × 10−6 to 1600 × 10−6 and from 19500 × 10−6 to 2100 × 10−6 with the reduction ratio of 88.1% and 89.2%, respectively. The recycled magnetic powder presents improved magnetic properties with Ms of 1.306 × 10−1 A∙m2/g, Mr of 0.926 × 10−1 A∙m2/g, Hcj of 1.170 T, and (BH)max of 125.732 kJ/m3, which reach 99.8%, 99.4%, 95.9%, and 96.9% of the original magnetic powders, respectively.