Assessment of Leaching Characteristics for Cerium and Cesium as Surrogates for Radioactive Materials

The leaching behavior of cerium and cesium from different mixtures of rapid setting cement (RSC) with deionized water (DIW) and artificial seawater (ASW) under both dynamic and static leach conditions was investigated according to the method in American National Standard ANSI/ANS-16.1-2003. The leachate solution was collected, diluted with HNO3, and analyzed using inductively coupled plasma–mass spectrometry after leaching periods of 2, 7, and 24 h and 2, 3, 4, 5, 14, 28, 43, and 90 days. Two models [the first-order reaction model (FRM) and the diffusion model (DM)] and their combination [the first-order reaction/diffusion model (FRDM)] were fitted to assess the leaching parameters and identify the type of immobilized radionuclides in the RSC matrix. The result indicated that leaching of 140Ce and 133Cs from the RSC matrices with DIW and ASW under both dynamic and static leach conditions was less than 20% and suggested that the leaching behavior of 140Ce and 133Cs approximated that of a semi-infinite medium. The leaching phenomena of 140Ce and 133Cs could not be fully represented with a single model (the FRM and the DM), and the FRDM was best fitted to these experimental data sets. Overall, the average leachability index L values for 140Ce and 133Cs were greater than the minimum limit indicating their acceptance for disposal recommended by the International Atomic Energy Agency. It could also be stated that RSC with DIW or ASW had a potential for immobilizing radioactive materials.