Selective Separation of Rare Earth Elements from Malic-Acid NdFeB Magnet Leachate by Solvent Extraction

Abstract The recycling of secondary resources containing rare earth elements (REEs) is a crucial strategy for meeting the growing demand for these critical materials and reducing reliance on primary mining. In recent years, organic acids (citric, maleic, acetic, malic, and oxalic acid) have been applied as sustainable lixiviants for the leaching of REEs; however, downstream purification of the resulting solutions remains less explored. In this work, solvent extraction was employed to recover and purify REEs from malic acid leachates of NdFeB magnets using different types of extractants: acidic (D2EHPA, Cyanex 272), ion-pair (Aliquat 336), and solvating (TBP). Among the tested extractants, di-(2-ethyl hexyl) phosphoric acid (D2EHPA) showed the highest extraction efficiency, although co-extraction of Fe was also observed. Optimal stripping was achieved using 0.7 mol L −1 HCl at 20°C, an aqueous/organic (A/O) ratio of 1, and 10-min contact time, yielding an aqueous solution containing 3.1 g L −1 Nd, 1.4 g L −1 Pr, and 0.1 g L −1 Dy, with a relative purity of 99.3 wt.% for REEs. These findings demonstrate the potential of combining malic acid leaching with D2EHPA-based solvent extraction as a sustainable route for REE recovery. However, challenges remain regarding the efficient stripping of Fe from D2EHPA, which requires further investigation to improve process performance.