Chemical properties of chromium oxide in kf-naf-alf3 Based Low Temperature Electrolyte Melt

Abstract

Chromium oxide is considered as one of the candidate lining materials for low temperature aluminum electrolysis. The chemical properties of chromium oxide in KF-NaF-AlF3 based low temperature electrolyte melt were studied by means of static oxidation tests and electrolysis experiment with vertical inert anodes. The results showed that trivalent chromium oxide (III) could be oxidized to generate different valence states chromates (II, III, IV, VI) in electrolyte melt. Among them, the hexavalent chromates could be volatilized in large amount with electrolyte volatiles. The strength of the oxidizing atmosphere was the key factor affecting the generation of yellow hexavalent chromates which could be significantly reduced by the existence of protective atmosphere and graphite. Under the condition of electrolysis with inert anodes, there was not only the massive formation and volatilization of hexavalent chromates, but also the pseudo volatilization of chromium oxide (III) caused by hot-oxygen.