Studies on electrolytically generated vanadous complexes used in decontamination formulations

Abstract

The 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 (<i>k₁=</i>3.45×10^-3<i> </i>min^-1) and a slower second stage (<i>k</i>₂=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.