Titration curves, column experiments, and reactive transport models


Titration curves, column experiments, and reactive transport models

Britz, S. M.; Noseck, U.; Brendler, V.; Stockmann, M.

Surface reactions related to e.g. transport and retardation processes in groundwater systems are correlated with geochemical conditions that vary in time and space. For longterm safety analysis of radioactive waste repositories it is of great interest to better understand and to realistically assess these geochemically driven surface and transport reactions, since they might strongly impact radiation exposure. To get an advanced insight into these processes column experiments are conducted and subsequently modeled with the geochemical speciation code PhreeqC, Version 2.18 (coupled with UCODE_2005). In order to set-up realistic reactive transport models so-called surface complexation parameters (SCP) such as surface site density, specific surface area, and protolysis constants need to be derived from titration experiments of relevant mineral phases. Two different titration techniques are conducted for muscovite and orthoclase: continuous and batch titration. Derived results are compared offering an insight into pHinfluencing reactions that contribute to surface reactions but also to cation exchange and mineral dissolution. In column experiments diffent solids are applied: natural sediments from the Gorleben site, Germany and pure mineral phases (orthoclase, muscovite, quartz). Parameters such as pH, ligands, ionic strength, and cation concentrations are varied in each experiment to reflect realistic enviromental conditions. Moreover, transient pH conditions are applied in selected columns.
Both types of experiments (titration, column experiments) including each geochemical variation provide data to model reactive transport processes of hazardous pollutants more realistically in groundwater-flow driven environments with PhreeqC. Calculations will be conducted and first results offered for discussion.
This project is funded by the German Federal Ministry of Economics and Technology (BMWi) under contract no. 02 E 11072A and 02 E 11072B.

  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy

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Publ.-Id: 19727