Simultaneous separation of iodide and cesium ions from dilute wastewater based on PPy/PTCF and NiHCF/PTCF electrodes using electrochemically switched ion exchange method

Abstract

Radioactive iodide (I−) and cesium (Cs+) ions were first simultaneously separated using electrochemically switched ion exchange (ESIX) method based on polypyrrole (PPy) and nickle hexacyanoferrate (NiHCF) films, which were chemically deposited on two porous three-dimensional carbon felts (PTCF), respectively. It was found that applied potential significantly facilitated the adsorption efficiency and the lower pH value was beneficial to the separation process. The maximum adsorption capacity of both ions approached above 95.3mg/g. The adsorption ratios of I− ion kept above 88% at pH value ranged from 1.89 to 9.36. The ultimate I− and Cs+ ion desorption rates were proximately 87% and 90%, respectively. Such separation was suggested to proceed in two main steps: an ESIX step in which electrochemical oxidation of PPy and electrochemical reduction of NiHCF occurred rapidly (the fast step), and an IX step which was controlled by the gradients of ion concentrations between films and bulk solution (the slow step). The separation factors (αClI=90 and αNaCs=458.8) showed high selectivity for I− (PPy film) and Cs+ (NiHCF film) ions over Cl− and Na+ ions, respectively. And five consecutive adsorption–desorption experiments indicated that the NiHCF/PTCF and PPy/PTCF electrodes can be effectively regenerated and are stable. It is expected that the developed method can be taken as a promising technology for actual wastewater treatment.