Batch- and titration experiments of single mineral phases are conducted in order to derive so-called surface complexation parameters that consist of protolysis constants (derived from titration curves), and surface site densities as well as stability constants of surface complexes of the according element-mineral composition (obtained from batch-experiments).

To verify the determined surface-complexation parameters and to verify the chosen bottom-up approach a mixture of minerals (synthetic sediment) is applied as a further batch-experiment with a similar experimental set-up as illustrated here. The bottom-up approach leads to the simulation describing sorption behavior of a sediment by means of each constituent.  The scope of this experiment is to model the sorption behavior of the synthetic sediment by applying the priorly assessed surface-complexation parameters. Modeled results should correlate well with the data resulting from batch-experiments that employ the synthetic sediment (verification of the chosen approach). The synthetic sediment is composed of 80% quartz and 10% muscovite, orthoclase, respectively, representing typical sediment of the Gorleben overburden.

Two solid/liquid ratios (M/V), three element-concentrations, and three pH-values ranging between 6 and 9 are applied:

• Mineral composition: 80% quartz, 10% muscovite, 10% orthoclase
• Solid/liquid ratio: 1/80 and 1/320 g ml^-1
• Element: Eu³⁺
• Concentration of Eu³⁺: 10^-5 mol L^-1, 5∙10^-6 and 10^-6 mol L^-1
• pH: 3 - 8
• Background solution: 0.01 mol L^-1 NaClO₄

Evaluation of Eu sorption on the synthetic sediment is still onging - results will be published the beginning of 2019.

References:

Noseck, U., Brendler, V., Flügge, J., Stockmann, M., Britz, S., Lampe, M., Schikora, J., Schneider, A., 2012. Realistic integration of sorption processes in transport codes for long-term savety assessments. GRS-297, BMWi-FKZ 02E10518, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH, Braunschweig, 293 p.

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