Tuning Malonamide Ligands for Ultra-High Separation of Iron from Rare Earths in Chloride Media: A Structure-Activity Study for NdFeB Magnet Recycling

The recovery of rare earth elements from waste neodymium magnets is of great economic and environmental significance. As the most widely used rare earth permanent magnet material, neodymium magnets contain a substantial amount of iron (approximately 60-70wt%). The chemical behavior of iron closely resembles that of rare earth elements, making the separation process highly challenging. To address the issue of efficiently separating iron and rare earth elements from neodymium magnets, this paper systematically investigates the extraction and separation behaviors of a representative rare earth element, Pr3+, and Fe3+ using a series of malonamide extractants (MAs) in hydrochloric acid medium. Seven malonamide extractants with different structures were synthesized and characterized. The effects of extractant concentration, temperature, hydrochloric acid concentration, and diluent type on the distribution ratios and separation efficiencies of FeCl3 and PrCl3 were examined in detail. The results demonstrate that by precisely controlling the acidity of the hydrochloric acid solution, this class of extractants can preferentially extract iron while efficiently retaining rare earths in the aqueous phase. Using 0.2mol/L DEDOMA to treat the NdFeB leaching solution resulted in an iron extraction efficiency of 99.70%, whereas the extraction efficiency of the rare earth elements (Nd, Pr, and Dy) was less than 1%. This study provides an important theoretical basis and technical reference for developing novel, efficient, and environmentally friendly rare earth separation systems, particularly for the removal of iron impurities from complex hydrochloric acid leach solutions.