The Effect of the Second Coordination Sphere on Vanadium Speciation in Molten Chlorides

Vanadium speciation in a variety of alkali chloride based melts was studied in situ using high temperature electronic absorption spectroscopy. The experimental spectra were resolved into constituent Gaussian bands. Octahedral VCl 6 3– complex ions is the only soluble species of V(III). Oxidation of VCl 6 3– complexes or chlorination of V 2 O 5 , V 2 O 4 or V 2 O 3 by hydrogen chloride produces soluble vanadyl-based complexes. The results obtained indicate that the coordination environment of vanadyl-species in NaCl–2CsCl melts is different from the melts containing smaller cations. Anodic dissolution of metallic vanadium in chloride melts produces vanadium(II) ions. Increasing temperature and the mean radius of the salt-solvent cation resulted in changes of the electronic spectra as a result of shifting VCl 6 4– ↔VCl 4 2– equilibrium towards the tetrahedral complexes.