Iodine Removal from Carbonate-Containing Alkaline Liquids Using Strong Base Resins, Hybrid Resins, and Silver Precipitation

Abstract

The ability of several material types to remove aqueous iodine from a mildly alkaline, carbonate-rich nuclear waste stream was evaluated: strong base anion exchange resins (SBARs), hybrid resins, Ag-containing materials, and Bi-containing hybrid resins. A combination of batch testing and flow-through column testing was used in the evaluation. In batch testing, hybrid resins CHM-20, SIR-110-CE, and RTBI were shown to have high efficiency for the removal of both iodide and iodate simultaneously, while Ag-containing materials and SBAR demonstrated high capacity for iodide removal. One example of each material type (CHM-20, A532E, and Ionex 400) was further evaluated for their sorption isotherms and column performance. The Langmuir isotherm, or a Langmuir–Freundlich hybrid isotherm, best described the sorption of iodide to the CHM-20 hybrid resin and Purolite A532E. The Freundlich isotherm best described the uptake of iodate to CHM-20 and A532E and for both iodide and iodate to Ag-containing Ionex 400. In column testing, Purolite A532E had exceptional performance for overall iodide removal. However, with the capacity demonstrated, the A532E resin would exceed class C waste classification before breakthrough initiated, and column change-outs in processing would be dictated by eventual waste classification, not breakthrough. Ionex 400, a Ag-zeolite, was observed to degrade over time under mild alkaline column conditions, whereas the hybrid CHM-20 was limited in the single pass through design and would be best suited for applications where iodide and iodate are present and recirculation of the column effluent is feasible. This work highlights the feasibility of commercially available materials to separate radioiodine from liquid environments.