A facile process to optimize performance of regenerated Nd-Fe-B sintered magnets: Chemo-selective dissolution washing

In this work, the recycled Nd-Fe-B powders and regenerated Nd-Fe-B sintered magnets with low impurity content were successfully prepared from Nd-Fe-B magnet sludge via reduction diffusion (RD) method followed by a chemo-selective dissolution washing process. The chemo-selective dissolution effect of various solution (deionized water, dilute acetic acid solution, NH4Cl-methanol solution) was evaluated by impurity content and magnetic properties of the recycled Nd-Fe-B powder. The NH4Clmethanol solution can selectively remove impurities with minimal damage to the magnetic phase. Besides, the optimal NH4Cl concentration and liquid-to-solid ratio were investigated. As a consequence, the contents of Ca, O, and H after optimal washing process are reduced to 0.07 wt%, 0.31 wt% and 0.22 wt%, respectively. Hence, M-3 T is increased to 146.72 emu/g, which is 33% higher than that of the initial sludge. Then, the regenerated Nd-Fe-B sintered magnets with properties of Br = 11.66 kG, H-cj = 16.49 kOe, and (BH)(m) = 31.78 MGOe were successfully prepared by mixing with 40 wt% Nd4Fe14B alloy powders. Compared with the corresponding regenerated magnets washed with deionized water, the remanence and coercivity are increased by 18% and 59%, respectively.(c) 2022 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.