131I Sorption by Thermally Treated Hydrotalcites

María Teresa Olguín1, Pedro Bosch2, Dwight Acosta3 and Silvia Bulbulian1
1 Instituto Nacional de Investigaciones Nucleates, A.P. 18-1027, Col. Escandón, Delegación Miguel Hidalgo, C.P. 11801, México, D.F.
2 Universidad Autónoma Metropolitana, Iztapalapa, Michoacán y Purísima, A.P. 55-532, Iztapalapa, C.P. 09340,México, D.F.
3 Universidad Nacional Autónoma de México, Instituto de Física de la UNAM, Ciudad Universitaria A.P. 70-360, C.P. 04510, México, D.F.

Abstract: The sorption capacity of hydrotalcite (HT) and its calcined product (CHT) was evaluated for 131I 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 131I, 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 131I sorption at very low concentrations ( 10−14 M) was 0.04 × 10−14 meq of 131I 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.

Key Words: Hydrotalcites • 131I131I Sorption • Anion Exchange • Magnesium Aluminum Oxide • Radioactive Waste • Radioactive Decontamination • Thermal Treatment

Clays and Clay Minerals; October 1998 v. 46; no. 5; p. 567-573; DOI: 10.1346/CCMN.1998.0460510
© 1998, The Clay Minerals Society
Clay Minerals Society (www.clays.org)