Rare metals preparation by electro-reduction of solid compounds in high-temperature molten salts

Direct electro-reduction of solid compounds in molten salts is a simple and straightforward electrolytic metallurgical method, which outperforms traditional pyrometallurgical methods such as carbothermic and metallothermic reductions in terms of economic viability, energy efficiency and carbon footprint. To better highlight the features of the direct electro-reduction of solid compounds in molten salts in extraction of rare metals, the scope of this paper is focused on the know-how of the cathodic process of the direct electro-reduction of solid compounds in molten salts in extraction of rare refractory metals including Ti, Zr, Hf, V, Nb, Ta, Mo and W, and rare disperse metals including Ga and Ge. In line with an introduction of the basic concept of the method, the characteristics of reaction paths in different systems are summarized and the corresponding strategy on tailoring energy efficiency and microstructure of electrolytic products are rationalized. The economic competence of the method might be enhanced by extending the method to controllable production of rare metals with high added values, well-defined microstructure and intriguing functionality. Direct electro-reduction of solid compounds in high-temperature molten salts emerges as an affordable, green, and controllable preparation of rare metals, in which, reaction paths show a significant influence on energy efficiency, composition/microstructure of electrolytic products and the economic competence of the process.