Extraction Equilibrium of Valuable Metals from NdFeB Permanent Magnet Using Carboxylic Acid as Extractant

The present study investigates the separation and recovery of the valuable metals in the sintered NdFeB permanent magnets by solvent extraction, in which neodymium, dysprosium and cobalt are contained as valuable metals. Neo-decanoic and naphthenic acids, and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) and bis(2-ethylhexyl) phosphoric acid (D2EHPA) were used as the metal extractants of carboxylic and organophosphorus acids, respectively, to evaluate the separability of the metals by the liquid-liquid extraction equilibrium. With the single metal ion systems, the distribution ratios of the respective metal ions with D2EHPA were the greatest, followed by those with PC-88A, neo-decanoic acid and naphthenic acid. Although the separation of these metal ions with organophosphorus acids were more effective than those with carboxylic acids, the carboxylic acids showed the sufficient separation efficiency to separate these metal ions. Moreover, the stripping operation with the extractant could be conducted in a relatively high pH range compared to the organophosphorus acid extractants. According to these results, the extraction equilibrium using neodecanoic acid extractant was measured with binary metal ion systems to study the effects of the coexisting metal ions. While the ferric and rare earth elements had little influence on the extraction equilibrium, cobalt ion was coextracted by the ferric or rare earth element ion, thereby making the separation efficiency lower. Then, based on consideration of these trends of extraction equilibrium, the separation scheme to recover the valuable metals in the sintered NdFeB permanent magnet is suggested.