Encapsulation of iodine-loaded adsorbents in blended Portland cement and geopolymer wasteforms

Abstract

Capture of radioiodine by solid adsorbents and subsequent cementation is a promising solution to achieve “Near Zero” emissions from nuclear fuel cycles. We investigate cementation of iodine-loaded silica adsorbents in blast furnace slag blended Portland cement (BFS:PC) and metakaolin-based geopolymers, and subsequent leaching in deionised water. Adsorbent encapsulation retarded BFS:PC hydration, but not geopolymer reaction. Phase assemblage was unaffected by adsorbent encapsulation for both BFS:PC and geopolymers, which comprised calcium aluminosilicate hydrate and potassium aluminosilicate hydrate gels, respectively. Adsorbents were encapsulated intact within BFS:PC, whereas adsorbents dissolved in the high pH of fresh geopolymers. BFS:PC exhibited low leaching stability and an alteration layer, however minimal iodine leaching occurred due to intact absorbents. Geopolymers showed high leaching stability, however adsorbent degradation resulted in significant iodine leaching. This evidences potential for cementation of radioiodine-loaded adsorbents under mild conditions, and highlights the importance of synergy when designing adsorbents and wasteforms for radioiodine abatement.