Experimental adsorption studies on different materials selected for developing a permeable reactive barrier for radioces
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Experimental adsorption studies on different materials selected for developing a permeable reactive barrier for radiocesium retention Miguel García-Gutiérrez1, Tiziana Missana1, Ana Benedicto1, Carlos Ayora2 and Katrien DePourcq2 1 CIEMAT, Departamento de Medioambiente, Av. Complutense 40, 28040 Madrid (SPAIN). 2 IDAEA-CSIC, Jordi Girona 18-26, 08034 Barcelona (SPAIN) ABSTRACT Cs-137 was accidentally spilled in an industrial waste repository located in a salt marsh in southern Spain, and a permeable reactive barrier was proposed to retain it. Cs adsorption properties of different natural clayey materials were analyzed. The salt marsh waters show high salinity and high chemical variability, therefore Cs adsorption was also analyzed in the presence of competitive ions, especially K+ and NH4+. Cs adsorption was non-linear in all the analyzed materials, indicating more than one adsorption sites with different selectivity. It was shown that in mixed clay systems with illite, montmorillonite and kaolinite, the presence of illite favors Cs retention at low and medium Cs loadings and montmorillonite at high Cs loadings. In the presence of illite and montmorillonite, kaolinite plays almost no role in Cs retention. The presence of K+ and NH4+ significantly hinders cesium adsorption.
INTRODUCTION Cs-137 is a major radionuclide in spent nuclear fuel and in the global radioactive waste inventory. It has been accidentally introduced in the environment by nuclear accidents and from nuclear weapons testing. Radiocesium is particularly relevant from an environmental point of view because it exists predominantly as the monovalent highly soluble cation Cs+. Geochemical barriers can be designed to retard or stop its migration in groundwater from contaminated zones: many solids are still under study for cesium retention [1,2] but the barriers comprised of argillaceous materials, are reported to be the most effective for its retardation [3]. Thus in this work, for the development of geochemical reactive barrier for cesium, different clayey materials were analyzed to measure their sorption capacity and to understand which minerals contribute most to cesium retention. In order to make the barrier permeable (clays usually have very low permeability) the sorbing fraction will be mixed with other materials, for example, wood shavings with a null sorption capability. Cesium retention occurs in clays mainly by ionic exchange; therefore the salinity of the waters and ion competition are expected to hinder its retention. The Spanish region, where Cs-137 was accidentally spilled, was located in a salt marsh. The salt marsh waters, affected by the tide, show very high salinity and high chemical variability, therefore Cs adsorption was analyzed
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under saline condition and in the presence of ions like potassium and ammonium potentially competitive for Cs adsorption [4,5] EXPERIMENTAL Sorption on three different clayey materials (Rojo Carboneros (RC), San Juan (SJ) and Canal de Drenaje (CD)) will be analyzed in this study using 2 different natu
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