Eco-Friendly Facile Three-Step Recycling Method of (Nd-RE)<sub>2</sub>Fe<sub>14</sub>B Magnet Sludge and Enhancement of (BH)<sub>max</sub> by Ball Milling in Ethanol
Syed Kamran Haider, Jin‐Young Lee, Dong-Soo Kim, Young Soo Kang
Abstract
A new recycling method of (Nd-RE)2Fe14B (RE = Pr, Nd, Tb, Dy) magnet sludge has been reported in this work. (Nd-RE)2Fe14B sludge obtained during the cutting and grinding process of the (Nd-RE)2Fe14B magnet was dissolved in H2SO4 by leaching and then annealed at 1000 °C to obtain the oxides of RE and Fe. Boric acid and CaH2 were added to these oxides, and the mixture was pelletized. Then, a reduction–diffusion (R-D) reaction was carried out at 1000 °C under Ar gas. After removal of CaO (byproduct of R-D reaction) by washing with water, (Nd-RE)2Fe14B powder showed a (BH)max value around 6.6 MGOe. In order to remove CaO particles completely, ball milling was done in ethanol which removed CaO particles seven times more efficiently as compared to the washing with water. Efficient removal of CaO and crystallite modification after ball milling increased the (BH) max value of the recycled (Nd-RE)2Fe14B powder up to higher than 10 MGOe. In this method, any harmful reagent did not contaminate the environment as compared to the previously used physical methods where CO2, SO2, NOX, CH4, and bromo trifluoro-Halon 1301 are produced and left to the environment. SO2 and SO3 produced during the annealing step were dissolved in the water immediately.