Spectroscopic identifications of U(VI) species sorbed by the green algae Chlorella vulgaris

The green algae Chlorella vulgaris has the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 40 % of the uranium was bound by the algal cells. The uranium removal is almost complete at pH 5 and 6 under the given experimental conditions. Scanning electron microscopy and laser-induced fluorescence spectroscopy were used to characterize formed uranyl species in the selected pH range. Thus demonstrating the regular distribution of U(VI) on the cell surface. Fluorescence spectroscopic investigations of formed complexes outside/inside the cells indicate, the binding of U(VI) to carboxyl groups plays a dominating role at pH 3. Whereas a minor impact of organic phosphate compounds on the U(VI) sorption can not be excluded. In contrast the phosphate groups are mainly responsible for the removal and immobilization of U (VI) at pH 5 and 6 by formation of organic or/and inorganic uranyl phosphates.