Selective leaching of neodymium from <scp>NdFeB</scp> carbonyl residues using hydrochloric acid

Abstract An efficient recovery method of valuable metals from NdFeB carbonyl residues with ultra‐low rare earth content was developed. Selective leaching of NdFeB carbonyl residues was carried out using hydrochloric acid, and the leaching conditions were investigated and optimized. The experimental results showed that the optimum operating conditions for hydrochloric acid leaching were as follows: concentration of 2.5 mol/L, leaching temperature of 60°C, leaching time of 0.5 h, leaching solid–liquid ratio of 1:2 (g/mL), and rotational speed of 600 rpm during the leaching process. At this time, the leaching rate of neodymium in the carbonyl residues of NdFeB was 46.67%, and the leaching rate of iron was around 0.01%. The use of hydrochloric acid leaching had a high selectivity for Nd and Fe in the carbonyl residues. Neutralization and removal of impurities from the leach solution was carried out using NaOH and the pH of the leach solution was set to 4.0, at which time the removal of Fe was 76.52%. The neodymium in the leach solution was directly recovered by oxalic acid precipitation method, and the dosage of oxalic acid was 1.2 times of the theoretical dosage of oxalic acid, at which the recovery rate of neodymium was 96.38%, and the purity of the rare earth oxides obtained was 99.95%.