Separation of Cesium from High Ionic Strength Solutions Using a Cobalt Hexacyanoferrate-Modified Graphite Electrode

Abstract

Graphite electrodes modified with cobalt hexacyanoferrate (CoHCF) were used to investigate the feasibility of electrochemically (EC) controlled ion exchange for separation and transfer of Cs from high sodium wastes. A thin layer of CoHCF was formed on the graphite substrate. The surface CoHCF phase was highly selective to Cs+ in the presence of overwhelmingly higher concentrations of Na+ and K+. Cs+ was incorporated into the electrode at 0 V and expelled at +1.0 V. X-ray photoelectron spectroscopy (XPS) confirmed the EC control of the cesium flux and its association with the Fe oxidation state in the CoHCF phase. There was a good correlation between the electric charge passed through the electrode and the amount of Cs incorporated or released. The maximum share of charge associated with Cs+ incorporation is ca. 40%. The performance of the electrode was stable in the range of pH from 1 to 11, but it deteriorated at pH > 11. The CoHCF electrodes performed well in multicycle processes of Cs separation and transfer, but the impact of non-EC-controlled cation exchange and carryover by the porous substrate were also significant.