THERMOCHEMICAL STUDIES OF FELSPATHOID MINERALS RELATED TO RADIOACTIVE WASTE TREATMENT

The thermodynamic properties of four felspathoid minerals (sodalites) was investigated to predict the stability of the phases, species partitioning and their dissolution behavior. These anion-bearing sodalites represent a significant component of a multiphase waste form being considered for the immobilization of Hanford low activity radioactive (LAW). The multiphase fluidized-bed steam reforming (FBSR) waste form is produced by reacting caustic Hanford LAW with clay (kaolinite) in a steam reformer unit. Numerous semi volatile anions, Cl^-, F^-, SO₄^2-, I^-, and TcO₄^- present in the LAW stream are captured in the cage of feldsphathoid minerals, thus immobilizing them. The thermodynamic functions of the felspathoids were obtained using low temperature heat capacity measurements and high temperature oxide melt solution calorimetry. The structure and thermochemistry of the perrhenate sodalite, where Re serves as a close chemical analogue of Tc under oxidizing conditions, were determined and the thereafter was found to be more stable than the other sodalites.