Studies on electrolytically generated vanadous complexes used in decontamination formulations

Abstract

25-31The low oxidation state metal ion, V2+ being a strong reducing agent can be formulated /complexed with suitable chelating agents to obtain a significant dissolution (reductive) of iron oxides, commonly found on the primary system surfaces (iron base alloys) of water-cooled nuclear reactors. The relative strength of the complexes of V2+ (as formate) with different chelating agents, L such as picolinic acid, EDTA and citric acid is studied by measurements of redox potential and UV-Visible spectra. The decay kinetics of the reduction of water by V(II)-picolinate (as a typical case) (V2+ to V3+ conversion) under deaerated condition was estimated using redox potential values and decay was found to follow two stages of first order kinetics with a faster initial stage (k1=3.45×10-3 min-1) and a slower second stage (k2=3.84×10-4 min-1). The cation and anion exchange resin behaviour of the complexes/formulations in their different oxidation states with their derived species is reported and the V(III)-picolinate is shown to exist as an anionic species in formate medium. The use of V(II)-EDTA and V(II)-citrate for dissolution has an advantage as their oxidation (to V(III) stage) at higher concentration ca. > 7mM has not resulted in any precipitation / crystallization unlike in the case of V(II)-picolinate