Sorption behavior of thorium onto granite and its constituent minerals

The sorption behavior of thorium (Th) onto granite and its major constituent minerals, feldspar, quartz and mica were investigated by batch sorption experiments. Experiments were carried out under variable pH and carbonate concentrations. Distribution coefficients (K-d) decreased with increased carbonate concentrations and showed the minimal value at around pH 10. This sorption tendency was seen for all the rock and mineral samples, and it was due to the formation of aqueous hydroxo-carbonate complexes of Th in the solutions. The order of sorbability for Th was mica > feldspar > quartz approximate to granite. The sorption behaviors of Th were analyzed by the non-electrostatic surface complexation model with the Visual Minteq computer program. The K-d for granite were calculated by component additivity approaches. The model calculations were able to explain the experimental results reasonably well. It was shown that the sorption behavior of Th onto granite can be explained by the complexation with the surface sites of mainly biotite and feldspar.