An acid-free process for selective REE recovery from spent NdFeB magnets by room-temperature electrolysis

Abstract

Spent NdFeB magnets are valuable secondary resources of rare earth elements (REEs). However, their conventional recovery processes require high-temperature roasting and acid leaching, which cause high consumption of energy and chemical inputs, and generate massive salt wastewater pollution issues. In this study, room-temperature electrolysis was used to selectively recover REEs,while ZnCl₂ solution was used as the electrolyte and a double anode system was introduced. NdFeB magnets served as active anodes to produce REE ions and Fe²⁺. After ≥97.10% of Fe²⁺ was oxidized at the inert anode, it was hydrolyzed to Fe(OH)₃in situ to separate it from the REEs. Subsequently, Na₂SO₄ was added to form an RENd(SO₄)₂ precipitatewhile achieving the recycling of the ZnCl₂ electrolyte. Then, the NaOH solution was used to dissolve small amounts of Zn and obtain Nd(OH)₃. Fe(OH)₃ and Nd(OH)₃ were calcined to obtain Nd₂O₃ products and Fe₂O₃ by-products. In addition, the effects of the electrolyte solution concentration, current density, and temperature on NdFeB electrolysis and Fe²⁺ oxidation efficiency were further investigated. The developed green process achieved selective REE recovery from spent NdFeB magnets under acid-free and room-temperature conditions. The energy consumption of this process is 0.9078 kw h kg⁻¹ NdFeB and the chemical input is approximately half of that of traditional hydrometallurgy.