Sustainable production of rare earth elements by recycling NdFeB magnets through sulfation chemistry assisted water leaching process

Abstract

This study presents a comprehensive kinetic and experimental analysis of selective sulfation roasting of spent NdFeB magnets using Fe₂(SO₄)₃, followed by water leaching, to optimize the recovery of rare earth elements. The activation energy for the sulfation reaction was determined to be 205.9 kJ/mol, with the dominant mechanism function aligning with 1-(1-α)^2/3, indicating that the process was typically controlled by interfacial chemical reactions at the surface of the unreacted core. Key parameters including temperature, roasting duration, and Fe₂(SO₄)₃ dosage were systematically varied to identify optimal conditions for sulfation roasting and metal leaching efficiency. Under the optimized conditions (i.e., a roasting temperature of 700 °C, roasting time of 240 min, and a nFe₂(SO₄)₃:n(RE + Fe) molar ratio of 2:1), leaching efficiencies of 96.4 %, 98.7 %, and 87.6 % were achieved for Nd, Pr, and Gd, respectively, while Fe leaching remained minimal at 0.01 %. The leaching residue was rich in hematite (Fe₂O₃), suitable for applications in iron and steel production.