Development of an electrically switched ion exchange process for selectiveion separations

The electrically switched ion exchange (ESIX) process, being developed at P acific Northwest National Laboratory, provides an alternative separation me thod to selectively remove ions from process and waste streams. In the ESIX process, in which an electroactive ion exchange him is deposited onto a hi gh surface area elecrotrode, uptake and elution are controlled directly by modulating the electrochemical potential of the film. This paper addresses engineering issues necessary to fully develop ESIX for specific industrial alkali cation separation challenges. The cycling and chemical stability and alkali cation selectivity of nickel hexacyanoferrate (NiHCF) electroactive films were investigated. The selectivity of NiHCF was determined using cyc lic voltammetry and a quartz crystal microbalance to quantify ion uptake in the film. Separation factors indicated a high selectivity for cesium and a moderate selectivity for potassium in high sodium content solutions. A NiH CF film with improved redox cycling and chemical stability in a simulated p ulp mill process stream, a targeted application for ESIX, was also prepared and tested. (C) 1999 Published by Elsevier Science B.V.