Chemistry of vanadium chlorides in molten salts: An electronic absorption spectroscopy study

The chloro and oxy-chloro complex ions of vanadium, containing the metal in different oxidation states (II, III, IV and V), were investigated in the melts NaClCsCl (at 550–700°C) and NaClKCl (at 680–980°C) under a variety of conditions. Melts were examined using electronic absorption spectroscopy between 4,000 and 33,000 cm−1. Anodic dissolution of vanadium was studied in NaClKCl melts at various anodic current densities. Vanadium dissolves, forming V(II) ions, at current densities of 100–150 mA cm−2; increasing the current density above ca. 340 mA cm−2 leads to the formation of predominantly V(III) species. Reactions of vanadium metal and vanadium oxides (V2O3 and V2O4) with hydrogen chloride or chlorine were followed by in situ spectroscopy measurements. Depending on the experimental conditions, a range of vanadium chloro- and oxychloro-complexes was formed. Reaction of the V(III) chloro-complex with oxygen leads to the formation of VO(II) complex ions. Preliminary results indicate that the V(IV) chloro-complex, VCl6 2−, can be formed by oxidising VCl6 3− with chlorine. Vanadium(V) oxide reacts with hydrogen chloride in NaClKCl melts to form an oxygen-containing complex of V(III). Direct dissolution of V2O5 in NaClKCl melts yields sodium polyvanadate, NaV6O15.