Study on the regeneration of the decontamination liquid waste containing V-Fe-picolinate complexes by the resin-filled electrodialysis

Abstract

Studies on the electrodialytic regeneration of simulated decontamination waste solution containing vanadium(Ⅲ), iron(Ⅱ) and picolinic acid (2-pyridinecarboxylic acid) were carried out using a resin-filled electrodialyzer. The ion exchange reaction, distributions of vanadium(Ⅲ)- and iron(Ⅱ)-picolinate complexes have been simulated and evaluated at different pH values and with various compositions of the model LOMI (Low Oxidative-State Metal Ion) solution. The effects of filled resin within the electrodialyzer on iR-drop reduction for the transport of ionic species in the dilute solution, the separation efficiency of cations, and the electrochemical regeneration of the exhausted resin were investigated. The complexation equilibria of vanadium and iron ionic species in the presence of picolinate ligand have been evaluated at different pH values and various compositions of the model LOMI formulation. Computer calculations for the multiple complexation equilibria could predict the speciation of metal picolinate complexes. Ion exchange column operations were carried out in order to elucidate the pH dependence of the cation exchange reactions of the simulated decontamination solution. The B-group model, that both cationic and neutral species are preferable species for uptake, could describe the ion exchange behaviour of the simulated waste solution containing vanadium(Ⅲ) and iron(Ⅱ) picolinate complexes. In the feed at pH 4.5, most of vanadium(Ⅲ) ions exist in the form of neutral vanadic hydroxy bis picolinate, $Ⅴ(Ⅲ)(Pic)_2(OH)$ complex, and iron(Ⅱ) ions are ferrous tris picolinate, $Fe(Ⅱ)(Pic)_3^-$, $Fe(Ⅱ)(Pic)_2$ complexes. However, these complexes are converted to the positively charged form due to the presence of hydrogen ions. Therefore, the converted cationic complexes are easily adsorbed on a cation exchange resin bed. The performance of the resin filled electrodialyzer was evaluated by measuring the current-potential relationship. The conductivity of the resin...