Electrically switched ion exchange (ESIX) for the removal of potassium to enhance water recycle opportunities

Electrically switched ion exchange (ESD), an electrochemical separation technique, is being developed at the Pacific Northwest National Laboratory (PNNL) for ion separations in industrial process and waste streams. ESIX provides an alternative separation method to conventional ion exchange technology. While ESIX is being developed for general ion separations [1,2], this paper focuses on the selective removal of potassium cations. Nickel hexacyanoferrate (NiHCF), an ESIX material, is shown to be selective for potassium over sodium with a separation factor of 24. In addition, NiHCF has been stabilized to over 15,000 cycles in a solution of electrostatic precipitator catch. To accurately model the impact of potassium and chloride buildup due to increased recycle of mill effluent streams, new simulation tools have been integrated into WinGEMS. Simulation is then used to evaluate recycle strategies and how new technologies like ESIX impact potassium and chloride levels throughout the mill. The Kraft recovery furnace simulation model has been enhanced to handle potassium and chloride compounds. Results from a full mill simulation show that using ESIX to treat the precipitator catch from the recovery boiler can lower the potassium levels in "as fired" black liquor by 35%, thus decreasing ash and dust stickiness.