131I- sorption by thermally treated hydrotalcites

The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for I-131(-) sorption from water solution and it was determined as a function of the calcining temperature. The radionuclide content was determined by gamma-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 I-131(-), sorption capacity was found to be 0.24 meg 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 meg g(-1) (63% of the AEC) and the HT structure was reconstructed. The I-131(-) sorption at very low concentrations (10(-14) M) was 0.04 x 10(-14) meg of I-131(-) g(-1) in the noncalcined HT, but for calcined samples at 773 K, the sorption increased to circa 0.97 X 10(-14) meg 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.