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

Abstract

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 (V 2O 3 and V 2O 4) 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, VCl 6 2−, can be formed by oxidising VCl 6 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 V 2O 5 in NaClKCl melts yields sodium polyvanadate, NaV 6O 15.