Sorption of biotite

Gneissic rock types are common in the coastal regions of the Baltic Sea and in the area of the planned deep repository at Olkiluoto. Based on experimental data and molecular modelling of mineral surfaces, the chemical reactions governing the sorption of Ni(II) and Eu(III) were interpreted using well-established thermodynamic sorption models. Two biotites were selected for the experiments and were characterised: they differ according to their origin, they were not pure biotite, but included other mineral phases, too, and they included other exchangeable cations than potassium alone. The titration experiments were performed on both biotites. The sorption experiments with nickel and europium on the biotites were successfully carried out, as was their modelling. The adsorption modelling was supported by molecular-level calculations to obtain an insight into biotite surface at the molecular level. It was possible to compare differences between potassium and nickel on minerals surfaces.