Organometallic functionalized clays for technetium immobilization

Nuclear waste repository designs require backfill materials to contain long-lived radionuclides, including technetium-99, present as the pertechnetate anion (TcO ₄ ⁻) under oxic repository conditions and mobile in the environment. Bentonite has been proposed as a suitable backfill material, and it is composed of montmorillonite clay, which can be functionalized to optimize its performance for TcO ₄ ⁻ sorption. In the current work, bentonite clay is functionalized with organic and inorganic moieties, and the impact of dual functionalization on TcO ₄ ⁻ sorption is investigated. The results show that the ordering of the functionalization is essential and that adding metal to an organoclay improves TcO ₄ ⁻ sorption compared to either the reverse ordering or the organic/inorganic clay alone. Furthermore, the TcO ₄ ⁻ sorption to the organometallic clays was consistent with either chemisorption or cooperative sorption, with a multi-step mechanism determining the kinetics of sorption.