Montmorillonite as barrier material for uranium(VI) at high ionic strengths


Montmorillonite as barrier material for uranium(VI) at high ionic strengths

Fritsch, K.; Schmeide, K.

Clay and clay minerals are potential host rocks for nuclear waste disposal due to their high sorption capacities and low permeability. Thus far, research of radionuclide retention by clays has been focused on low ionic strength systems. The present work addresses North German clay deposits whose groundwaters show ionic strengths up to 4 mol/l in depths relevant for nuclear waste disposal.[1] The experimental set-up is modelled on conditions found in the Konrad mine, which serves as reference site. Montmorillonite is used as model clay for uranium sorption and diffusion experiments in sodium and calcium chloride as well as in a mixed electrolyte that resembles the groundwater at the Konrad site.
Ionic strengths effects, where sorption decreases with increasing ionic strength, can generally only be observed in the acidic pH range because they depend on cation exchange. Natural groundwaters at the Konrad site have pH values > 5.5, where cation exchange has ceased to be the predominant sorption mechanism for U(VI), which in turn diminishes ionic strength influence. The sorption maxima in different salt systems lie slightly below the neutral point and within the pH range of groundwaters of the reference site. When approaching the ionic strength of North German groundwaters, sorption becomes partly irreversible.[2] Furthermore, uranium retention greatly increases with ionic strength in the alkaline pH range in the calcium chloride system. Both effects are attributed to secondary phase formation, which is promoted by increasing ionic strength. Additionally, spectroscopic results and surface complexation modelling of the system will be presented.
[1] Brewitz, W. et al. (1982) Eignungsprüfung der Schachtanlage Konrad für die Endlagerung radioaktiver Abfälle. GSF-T 136.
[2] Zehlike, L. (2013) Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit, Bachelor thesis, TU Dresden.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength

  • Contribution to proceedings
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland
    Proceedings of the 7th Mid-European Clay Conference
  • Lecture (Conference)
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland

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Publ.-Id: 20461