Physicochemical evolution of a geopolymer wasteform for immobilizing thermally treated spent ion exchange resins: structural changes and cesium leachability

Abstract

Thermally-treated spent ion-exchange resins (OIXRs) were immobilized by mixing 1 wt% ash with a metakaolin geopolymer. Stable 133Cs simulated 137Cs. Year-long semi-dynamic leaching experiments at pH 12.5 monitored changes in pH, conductivity and dissolved ions. Na, Al, Si were rapidly released into solution and 32% of Cs leached within 28 days. Ca uptake dominated, driving Na-Ca exchange and progressive N–A–S–H to C–A–S–H transformation. XRD, FE-SEM–EDX and 27Al/29Si MAS-NMR showed depolymerization, Ca-rich precipitates and loss of tetrahedral Al. Despite 59% Cs loss after 1 year, results demonstrate the matrix’s long-term chemical evolution and its promise as a sustainable OIXR wasteform.