Contribution of minerals to the sorption of U(VI) on granite

Batch sorption experiments of U(VI) onto the surfaces of granite rock were carried out. The distribution of the sorbed U(VI) on crushed granite particles was investigated via a sequential chemical extraction method to quantify the amount of U(VI) sorbed on the mineral phases and by X-ray diffraction characterization of dried samples of the remaining minerals after each extraction step to determine the significant mineral phases that sorb U(VI). Chlorite among the constituent minerals, even though being present in a small amount, is assumed to contribute to the strong U(VI) sorption and most of the sorbed U(VI) was weakly bound to the granite surfaces. However, a discriminative amount of the sorbed U(VI) on granite particles was difficult to desorb, in particular, when sorption took place in the alkaline region. The distribution of the sorbed U(VI) both on the fresh intact surface and on the natural fracture surface was also investigated by a X-ray image mapping technique. The result shows that dominant minerals hosting the majority of the sorbed uranium are mica for the intact surface of granite and chlorite for the fracture surface of the granite.