Selective acid leaching of rare earth elements from roasted NdFeB magnets

Acid leaching of Nd and Fe from roasted NdFeB magnet powders was studied in stirred-tank and packed-bed reactors. The experimental data at sulfuric acid concentrations of 0.02-1.0 mol/L and at 80 degrees C were correlated using a diffusion-reaction model assuming homogeneous distribution of the constituents in the magnet. The results show that the experimental data can be correlated well when formation of NdFeO3 during roasting is taken into account. Decomposition of NdFeO3 to Nd3+(aq) and Fe3+(aq) is the main route in neodymium dissolution from roasted NdFeB. The model parameters derived from stirred-tank data predict reasonable well leaching in packed-bed reactor. In both systems, re-precipitaion of iron due to acid depletion allows selective dissolution of Nd and other rare earth elements.