Acetic acid leaching of rare earth elements from e-waste magnets: process optimization and kinetic evaluation

The transition to a low-carbon energy system has increased the demand for rare earth elements (REEs), essential for wind turbines and other renewable energy technologies. However, the limited and geographically concentrated supply of REEs challenges the energy transition. In this context, electronic waste recycling, particularly obsolete hard disk drive (HDD) magnets, emerges as a sustainable strategy to mitigate supply risks. This study evaluated the leaching of REEs from HDD magnets using acetic acid as a lixiviant agent. Characterization of magnets from different manufacturers revealed chemical similarities, allowing their joint processing and recycling. The leaching experiments at 50 °C, 3.0 molL^-1 CH₃COOH for 2 h, and S/L ratio of 1/12 resulted in 18.4 gL^-1 Nd, 2.9 gL^-1 Pr, 1.2 gL^-1 Dy. The kinetic study indicated that the leaching process follows a mixed-control mechanism involving both diffusion through a product layer and surface chemical reaction. This conclusion was supported by the calculated activation energies and the visual observation of hydrogen bubble formation, which may hinder the diffusion of reactants and products, suggesting the simultaneous influence of multiple rate-limiting steps. These findings reinforce the feasibility of using organic acids for REEs recovery, highlighting their potential as a sustainable alternative to conventional leaching methods.