A molten salt metal-air electrolyzer for recycling superalloy

Recovering critical strategic metals from superalloy scraps is indispensable to sustaining the materials supply chain. However, the excellent physicochemical properties of superalloy make them difficult to dissolve and separate, thereby hindering their recycling and reutilization. Here, we design a molten salt metal-air electrolyzer (MMAE) that synergistically oxidizes and pulverizes scraps, which generates oxide powders that can be easily dissolved and separated for all element recovery. The corrosivity of molten chloride and electrochemical polarization can convert scraps at the anode into soluble metal chlorides, while oxygen is reduced to O^2- in the form of soluble CaO. Subsequently, the soluble metal cations encounter O^2- in molten CaCl₂-NaCl to precipitate as insoluble oxides. The MMAE constructs two dynamic metal/metal chloride and oxygen/CaO interfaces, achieving a high dissolution rate of 0.290 g/(cm²∙h). Subsequent roasting process preferentially extracts rhenium (Re) with a recovery efficiency of 90.46%, followed by selective separation and recovery of other metals with a recovery efficiency of >93% under low acid consumption. Life cycle assessment analysis shows its low energy consumption and environmental impact. Overall, the MMAE is a general method to recover a range of superalloy scraps, opening up an effective pathway for advancing sustainable metal recycling.