Enhanced electrodeposition and separation of metallic Cr from soluble K2CrO4 on a liquid Zn cathode

Abstract

Abstract Carbon contamination and the formation of low-valence oxides limit the preparation of refractory metals by molten salt electrolysis. In this paper, a liquid Zn cathode is adopted for the electrochemical reduction of soluble K2CrO4 to metallic Cr in CaCl2-KCl molten salt. It is found that CrO42- can be directly electrochemically reduced to Cr via a six-electron-transfer step and low-valence Cr oxides is hardly produced. The reduction rate is obviously increased from 16.7 mgCr h−1 cm−2 on the solid Mo cathode to 58.7 mgCr h−1 cm−2 on liquid Zn cathode. The electrodeposited Cr is distributed in liquid Zn cathode. Carbon contamination is effectively avoided due to the negligible solubility of carbon in the liquid Zn cathode. Furthermore, Cr can be effectively separated and enriched to the bottom of liquid Zn under super-gravity field, realizing the efficient acquisition of metallic Cr and recycling of liquid Zn. The method herein provides a promising route for the preparation of refractory metals with high-purity by molten salt electrolysis.