131 I − Sorption by Thermally Treated Hydrotalcites

The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131 I − sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by γ-spectrometry. Solids were characterized by thermal analysis, X-ray diffraction (XRD), electron microscopy and Brunauer-Emmett-Teller (BET) analysis. For 0.1 M Na I solution, labeled with 131 I − , sorption capacity was found to be 0.24 meq g −1 (7.2% of the anion exchange capacity, AEC). But, if the sample was previously calcined at 773 K and the HT structure destroyed, the sorption of I − increased considerably, up to 2.08 meq g −1 (63% of the AEC) and the HT structure was reconstructed. The 131 I − sorption at very low concentrations (10 −14 M ) was 0.04 × 10 −14 meq of 131 I − g −1 in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 × 10 −14 meq g −1 . Calcination temperature determines the surface area of the resulting mixed oxides, and that property seems to be the most important factor controlling the I − sorption. If the calcination temperature was increased to 873 K, the specific surface area of the oxide mixture increased and I − sorption increased as well, whereas calcination of HT at 973–1073 K resulted in a low surface area and a low I − retention.