RELATION BETWEEN COLLOID COMPOSITION AND THE ENVIRONMENT OF THEIR FORMATION - APPLICATION TO THE EL BERROCAL SITE (SPAIN)

In the framework of nuclear waste topics, the role of colloids is more and more emphasized in relation to the transport of radioelements in natural groundwaters. We attempt here to check if the nature and physi co-chemical characteristics of the colloids from the granitic site of El Berrocal are closely related to the bedrock composition. The colloi ds are studied in three types of groundwaters (sulfate and carbonate w aters in different redox conditions) as well as colloidal suspensions extracted from clayey materials present in the fractures. The particle size distributions are performed by photon correlation spectroscopy. Their chemical composition is obtained by X-ray microanalysis after tr ansversal ultrafiltration. The main results deal with the chemical com position of colloids. They are mainly composed of silica, aluminosilic ate phases, and Fe, Ti, Al oxyhydroxides. In the case of the carbonate and oxidized hydrofacies, traces of Mg, Cu, Zn, Ba, S as well as carb onate phases (Zn, Ca) occur. In the particular case of the sulfate hyd rofacies, traces of S, Mg, Cu are identified. Finally in the less oxid ized and carbonate groundwater, a lot of phases consist of sulphur wit h Cu, Zn, Fe as well as of carbonate with Cu, Zn, Fe, Ca and Mg. For t he clayey suspensions, colloids are mainly composed of illite and sili ca. In conclusion, the contribution of the bedrock as well as the infl uence of the physico-chemical conditions are discussed in order to dec ipher the role of neoformation and dispersion processes in the colloid formation.