Molten salt electrolysis of spent nickel-based superalloys with liquid cathode for the selective separation of nickel

Bearing significant concentrations of high value and critical metals, superalloy scraps are recycled to alleviate the current resource shortage. This paper presents a novel method of molten salt electrolysis coupled with a liquid cathode (Cd) for the selective nickel extraction from nickel-based superalloys. The method was inspired by the high corrosion resistance of superalloys, which makes recovery challenging, and the poor selectivity of existing nickel extraction methods. Electrochemical analysis was performed by cyclic voltammetry and linear voltammetry. Results indicated that Cr, Fe, and Ni were oxidized sequentially in the superalloy during electrolysis. The effects of electrolytic temperature and duration on the dissolution rate of the anode as well as the cathode composition were investigated. After electrolysis at an optimal temperature of 650 °C, SEM-EDS and XRD results revealed that the surface of the superalloy became porous, and nickel existed as NiF2 in the molten salt or as Cd-Ni liquid alloy in the cathode. Other superalloy elements, such as iron and chromium, existed in the electrolyte as alloy particles or fluorinated salts and were not detected in the liquid cathode. Therefore, the proposed method of molten salt electrolysis coupled with liquid cathode exhibited excellent selectivity toward Ni extraction from superalloy scraps.