Technetium / Nuclear fuel cycle / Medicine / Environment / Radionuclide generator / Radionuclide purity SummaryFormation of ''To in nuclear reactors and the fate of Tc in reprocessing plants are described. "Mo/'''"Tc radionuclide generators for use in nuclear medicine, the production of the importance of nuclear purity control and the selection of suitable Compounds of Tc are discussed. The ways by which Tc may enter the environment, the dissolution of TCO2 and the different migration and Sorption behaviour of Tc(IV) and Tc(Vll) are explained and the importance of the interaction of Tc with organic Compounds is emphasized.

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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Sorption of uranyl ions on Si0 2 • xH 2 0 (silica gel) is investigated in absence and in presence of carbonate as function of pH. The curves obtained are very similar to those observed for sorption of uranyl ions on Ti0 2 • xH 2 0, indicating the dominating influence of the uranium species in solution. Between pH 2 and 5 the sorption ratio R s increases with hydrolysis of uranyl ions (formation of U0 2 0H + ), around pH 7 it is nearly independent of pH, and at higher pH it decreases again. The equilibrium constants are calculated for these ranges. In presence of carbonate R s decreases drastically above pH 6, due to the formation of carbonato complexes in solution. Sorption of uranyl ions on Si0 2 · XH 2 0, on Ti0 2 · xH 2 0, and on cryst. Si0 2 and A1 2 0 3 is compared. The problems of "surface complexation" modelling are discussed.

Technetium! Hydrosphere/Geosphere jRedox Potential/SorptionSummaty The various pathways of Tc into the hydrosphere and the geosphere are summarized and the chemistry of Tc in natural waters is discussed. Sorption experiments with 5 selected sediments and 5 corresponding groundwaters of different salinity are described. Analytical data of the sediments and the groundwaters are presented and evaluated with respect to their influence on the chemistry of Tc. Sorption and desorption experiments are performed under aerobic and under anaerobic conditions (inert gas box).At higher redox potentials Eh (aerobic conditions) where TcOi is the stable species of Tc very low sorption ratios of about 0.1 to 0.3 ml/g are measured, the lower values being observed at higher salinity. The sorption of TcO, is reversible and explained by physical adsorption at the surface of the grains of the sediments.At low Eh (strongly anaerobic conditions) where TcO(OH)3 or T^, • 2 H,0, respectively, is the stable species of Tc high sorption ratios are measured (of the order of 10' ml/g at initial concentrations of 10"' mol/1 of TcO^) which do notdepend markedly on salinity, but at higher salinity the final sorption values are attained faster. Now, sorption is npt reversible and the irreversibleprocessistheformationofTcO(OH), orTcO, -21150, respectively, foUowed by strong sorption of this species. When Eh is increased, the sorption ratios drop rather sharply at 170±60mV.In all experiments only TcO, is found in Solution and no colloidal forms of Tc are detected.

Radioactive iodine /Iodine in groundwater / Sorption of iodine/ Carboniferous particles /Organics /Microorganism SummaryThe chemistry of iodine in the hydrosphere is discussed and the sorption of radioactive iodine on sediments from the layers above the salt dome at Gorleben is investigated at low and high salt concentrations. Special attention is paid to the carboniferous particles in the sediments and their influence on sorption of iodine. For this purpose the amount of carboniferous particles in the sediments is varied and the sediments are pretreated by heating and by addition of Η 2 0,. The influence of addition of NaCl is also investigated. The sorption of I ~ on the inorganic components of the sediments (the minerals) is rather small, as expected. It is mainly due to physical adsorption. The sorption of I" in the carboniferous particles, however, is very high. Iodine is taken up by these particles, in particular by the organic compounds and the microorganisms contained therein by very slow irreversible processes.

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