Electronic Absorption Spectra of Vanadium Species in Halide melts

摘要

Physico-chemical behavior of vanadium in chloride melts was studied using high temperature electronic absorption spectroscopy and spectroelectrochemistry. Dissolution of VCl_3 in molten chloride leads to the formation V(Ⅲ) species, VCl_6~(3-). Vanadium(Ⅱ) complex ions VCl_6~(4-) are formed during electroreduction of vanadium(Ⅲ )-containing melts and vanadium metal anodic dissolution. V(Ⅱ) chloro-species slowly react with silica to form an oxygen-containing insoluble phase. Due to high volatility of VCl_4 oxygen-containing vanadyl species, VOCl_4~(2+), is the only stable form of V(Ⅳ) in fused chlorides. It is formed when V_2O_5, V_2O_4 or V_2O_3 react with HC1. Electroreduction of vanadyl complexes leads to the formation of insoluble oxygen-containing vanadium(Ⅲ)species, whereas electrochemical oxidation has no effect on vanadium speciation, VO~(3+)/VO~(2+) red-ox potential is more positive than Cl_2/Cl~-. Further oxidation VO~(2+) species gives vanadate anions. The electronic absorption spectra of soluble vanadium species were measured in 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl mixtures at 450-750 °C.