Radionuclides iti the geosphere /Sorption ratios /Colloid formation/Radioactive Cs + ¡Radioactive Sr 2+ /Radioactive Ce 3+ Summary Natural systems comprising sediments and groundwaters of low and of high salinity are investigated with respect to the formation and the influence of coarsely dispersed particles and finely dispersed particles (colloids). Equations are derived for the sorption equilibria in such systems and it is shown that the efficiencies of mutual separation of coarsely dispersed particles, finely dispersed particles and sediments (efficiencies of filtering) strongly influence the sorption ratios that are observed.In groundwater without sediments the formation of colloids of radioactive Ce 3+ is demonstrated, whereas Cs + and Sr ì+ do not form colloids under these conditions, as expected.The amounts of elements and of colloids given off by the sediments into the groundwaters are measured for the samples of low and of high salinity and the influence of agitation is shown.Sorption ratios of radioactive Cs + , Sr î+ , and Ce 3+ are investigated as function of the ratio of the groundwater volume to the mass of the sediment without filtration, after filtration through 0.45 Mm filters and after ultrafiltration. The results are discussed on the basis of the equations derived. It is shown that Cs + ions are sorbed mainly on the clay particles and that the larger amount of these clay particles has grain sizes greater than 0.45 Mm under the experimental conditions of smooth shaking. Sr 2+ ions are mainly sorbed on the sediments with a relatively low sorption ratio. Ce 3+ ions form colloids ("Eigenkolloide") that are retained by ultrafiltration.
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