Influence of sulphuric acid concentration and solid/liquid ratio on leaching efficiency of rare earth elements from NdFeB postconsumer magnets

The recovery of rare earth elements (REE) was boosted by the 2010 crisis, when the supply of these metals fell sharply in relation to demand and prices were elevated. However, less than 1 % of these metals are recovered worldwide, mainly due to the problems with inefficient scrap collection and economically unprofitable processes. Significant quantities of REE are found in neodymium-iron-boron (NdFeB) permanent magnets present in computer hard disk drives. Therefore, this work aims to evaluate the effect of sulphuric acid concentration and solid/liquid ratio on the recovery of REE through a hydrometallurgical route. For this purpose, acid concentration and solid/liquid assumed each four level values. It was observed that neodymium (Nd) and praseodymium (Pr) reached values close to 100 % of leaching efficiency, however dysprosium (Dy) and Terbium (Tb) only about 45 %, due to differences in solubility. Also, it was noticed that low concentrations of sulfuric acid do not satisfactorily dissolve high solid/liquid ratios, meaning that an optimal arrangement was at intermediate levels of both factors. In addition, the analysis of residual material showed that the main chemical species after leaching batches are nickel and iron, however the REE leaching selectivity towards iron was low, since high content of iron was also leached.