Enhancing Cs retention in superabsorbent polymers via preferential Ca removal by CO2 bubbling in fly-ash aqueous systems

In this study, we aimed to safely treat fly ash generated during the incineration-based volume reduction of 137 Cs-contaminated waste from the Fukushima Daiichi Nuclear Power Plant accident by applying SAP to the fly-ash washing process. To enhance the Cs⁺ retention capacity of SAP, we investigated the removal of the interfering element Ca from fly-ash aqueous solutions by inducing CaCO 3 precipitation via CO 2 bubbling. When CO 2 bubbling adjusted the solution pH to an appropriate range, Ca 2+ concentrations decreased through CaCO 3 precipitation, thereby decreasing the distribution coefficient for Ca and enhancing that for Cs. This method is advantageous because it does not require chemical modification of SAP and avoids increasing the electrolyte concentration, which would otherwise reduce SAP water-absorption capacity.