Iodine speciation in cementitious environments

Abstract

Iodine-129 is a key risk driver in most low-level waste cementitious waste repositories. Objectives of this study were to determine iodine speciation in cementitious materials with slag (Grout+slag) and without slag (Grout–slag) and its impact on iodine immobilization. Irrespective of which iodine species was amended to the aqueous phase, there were no significant differences in uptake-Kd values (∼3 L/kg). However, when the various iodine species were hydrated with the grout, the release-Kd values (6.1–121.8 L/kg) were significantly greater than the uptake-Kd values, and the amended iodine speciation (I− ≪ org-I ≤ IO3−) and grout formulation (Grout–slag < Grout+slag) had a significant impact on release-Kd values. In grout samples amended with I− and IO3−, org-I was formed and comprised a majority of the iodine in the leachate after 28 days of equilibration. The formed org-I originated from organic carbon (C) in the grout material (∼1200 mg/kg C). For the first time, these studies demonstrate that multiple iodine species can co-exist simultaneously in grout porewater, the iodine species initially added to the grout can greatly affect iodine immobilization, and the addition of slag to the grout formulation increased iodine immobilization. These results may have important implications on radioiodine waste disposal.