LiNO3-assisted electrochemical extraction of metallic Sm from a molecular liquid-based electrolyte

Abstract

Developing efficient, green, and cost-effective methods for extracting rare earth (RE) metals is essential to accelerate breakthroughs in critical technologies in the field of RE-based functional materials. In this study, a low-cost aprotic polar molecular liquid, N,N-Dimethylformamide (DMF), was used for electrowinning metallic Sm with upstream SmCl3 as the raw material, inspired by previous applications of diverse specialised ionic liquids for the electrochemical recovery of RE metals. Cyclic voltammetry and electrodeposition experiments demonstrated that metallic Sm cannot be obtained from the binary DMF-SmCl3 system, but can be electrodeposited with LiNO3. Therefore, the mechanism underlying the observed electrochemical behaviour is elucidated and discussed in detail. Sm and Sm–Co metallic elements were successfully electrodeposited on an Al substrate at a relatively high current density, characterised, and evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Moreover, a unique two-step method involving electrodeposition and direct smelting is prospectively described for the continuous preparation of bulk RE-containing alloys to stabilise highly active RE elements. Therefore, this study provides valuable insights into practical solvometallurgical processes for RE metal extraction, refinement, and recycling.