Iodosodalite synthesis with hot isostatic pressing of precursors produced from aqueous and hydrothermal processes

Abstract

Iodosodalite powders were synthesized using aqueous (70 °C) and hydrothermal (180 °C) methods and then hot isostatically pressed (HIP), without or with (10 or 20 mass%) sodium borosilicate glass binders, at 900 °C and 175 MPa for 3 h to convert into glass-bonded iodosodalite waste forms. After HIPing, comparisons were made of the structures, compositions, morphologies, porosities, and chemical durabilities of the iodosodalite samples produced through aqueous and hydrothermal methods. X-ray diffraction patterns of HIPed samples showed that iodosodalite remained as the dominant phase. However, the iodosodalite phase concentrations decreased after HIPing, indicating iodosodalite decomposition (or amorphization) during the HIP process. Scanning electron microscopy and elemental mapping analyses on cross sections of HIPed samples showed homogeneous elemental distributions for aqueous-grown iodosodalite, whereas hydrothermally grown iodosodalite samples had greater heterogeneity and porosity. The densities of HIPed samples with more glass binder were generally higher than samples HIPed without binder. The leach tests on samples containing 20 mass% glass binder showed that the iodine dissolution rate of HIPed hydrothermally grown iodosodalite was about 4 × higher than iodosodalite grown with the aqueous method. This study provides alternative techniques for immobilizing iodine streams in iodosodalite waste forms.