Upcycling of Titanium by Molten Salt Electrorefining

Abstract

Molten salt electrorefining is expected to be a powerful technology for upcycling titanium scrap because of its robust ability of removing impurities. However, realizing the stable operation of electrorefining, for example, the current efficiency of the anode and the cathode is still a key challenge from the viewpoint of industrial applications. Here, we study titanium’s anodic dissolution and cathodic deposition processes via a direct three-dimensional visualization method based on a computed tomography technology under high-temperature operational conditions. Real-time quantitative results show that the current efficiency is obviously affected by the concentration of titanium ions in the melt. Visual analysis of the local dissolution rate and the curvature of the titanium anode at different electrolysis stages reveals the kinetic origin of the concentration-induced current efficiency changes, which arise from the priority of the side reactions being dependent on the concentration of titanium ions. Finally, we show that employing the high concentration and single existence forms of titanium ions is an effective strategy to prevent the side reactions and improve the current efficiency. This work provides a fresh and fundamental understanding of the side reactions occurring at the interface of electrodes and is significant for facilitating the stability of electrorefining engineering of titanium.