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

• Published in: Journal of rare earths 2023-12, Vol.41 (12), p.1976-1983
• Main Authors: Xu, Haibo, Lu, Qingmei, Yu, Lichao, Cong, Liying, Tian, Haowen, Liu, Weiqiang, Liu, Youhao, Wang, Yunqiao, Chen, Jingwu, Yi, Xiaofei, Wu, Qiong, Yue, Ming
• Format: Article
• Language: English
• Subjects: Chemo-selective dissolution; Magnetic properties; Rare earths; Recycling Nd-Fe-B magnet Sludge; Reduction diffusion; Washing process
• ISSN: 1002-0721; 2509-4963
• DOI: 10.1016/j.jre.2022.11.020

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 NH4Cl-methanol 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, M3 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, Hcj = 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. Recycled Nd-Fe-B magnetic powders with low impurity content was obtained by chemo-selective dissolution washing, thereby the magnetic properties of the regenerated Nd-Fe-B sintered magnets were optimized. [Display omitted] •The chemo-selective dissolution washing process can effectively reduce the impurity content of the recycled Nd-Fe-B powder and improve its magnetic properties.•The selective impurity removal effect of NH4Cl-methanol solution is the best, resulting in the highest M3T of the recycled Nd-Fe-B powder, which is 33% higher than the initial sludge.•The remanence and coercivity of the corresponding regenerated sintered magnets were increased by 18% and 59%, respectively, when washed with NH4Cl-methanol solution compared with those washed with deionized water.