Comparison of production of mixed rare earth oxide (Nd/Pr oxide) powders by different precipitation agents from NdFeB magnets’ water leaching

This research compared the production processes for mixed rare earth oxide (Nd/Pr oxide) powders from a leach solution obtained from acid baking with nitric acid followed by water leaching. Furthermore, the precipitation behaviour of the constituent elements in the leach liquor was examined. Development of economically feasible processes is significant on an industrial scale. In this regard, Nd/Pr oxide powders were recovered from the leach solution by using oxalic acid, ammonium oxalic acid (C₂H₂O₄), sodium hydroxide (NaOH), and ammonium hydrogen carbonate (NH₄HCO₃) in a comparative manner. Experimental investigations showed behavioural similarities between C₂H₂O₄ and NH₄HCO₃ precipitation agents; they precipitate rare earth elements (REEs), selectively. However, NaOH was different from them as it precipitates constituent elements in the leach liquor. The cost of C₂H₂O₄ and NH₄HCO₃ on the industrial scale is higher than NaOH. The resulting flow diagrams of the preparation of Nd/Pr oxide powders were comprehensively compared and optimised to propose more environmentally friendly, economical, and sustainable process.