Electrochemical refining of carbonitrothermic vanadium in CaCl 2 –NaCl–VCl 2 electrolytic bath

Abstract

A new vanadium intermediate, containing 94·4% vanadium, was successfully electrorefined to a purity of 99·8 mass-% in CaCl₂–NaCl–VCl₂ electrolyte. The impure vanadium was prepared by heating a mixture of vanadium pentoxide (V₂O₅) and graphite powder under flowing nitrogen atmosphere. Vanadium nitride, so prepared, was subjected to pyrovacuum heating to a temperature of 1750°C under dynamic vacuum (better than 0·05 Pa) to prepare vanadium sponge. The impure vanadium was then taken up for further refining in a molten salt electrolytic bath. The cathode current efficiency and metal recovery, under optimised conditions, were found to be 90 and 87% respectively. The hardness of the arc cast vanadium crystals (with a size ⩾840 μm) indicated the formation of a ductile grade vanadium metal. Scanning electron microscopy photographs of the coarse crystallites showed a dendritic morphology, consisting of primary, secondary, tertiary and quaternary branching.