Spectroscopic determination of U(VI) species sorbed by the Chlorella (Chlorella pyrenoidosa) fresh water algae

The green algae Chlorella (Chlorella pyrenoidosa) have the ability to bind high amounts of uranium(VI) in the pH range from 3 to 6. At pH 3 up to 20 % of the uranium is bound by the algal cells whereas the uranium removal by algal cell is almost complete at pH 5 and 6 in the concentration range of 4 x 10(-4) to 1.6 x 10(-3) M. Sorption capacities are in the range of 300-350 mg g(-1) and 250-280 mg g(-1) for fresh water and seawater respectively. Concentration of uranium was measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) by using two different emission spectral lines at 409.014 and 424.167 nm. Environmental scanning electron microscopy (ESEM) complimented with energy dispersive X-ray (EDX) is used to characterize the binding sites of uranyl species on algal cell in the selected pH range. The micrographs show a regular distribution of U(VI) on the cell surface. Attenuated total reflectance-fourier transform infrared (ATRFTIR) spectrum of Chlorella indicates that the binding of U(VI) either to phosphodiesters (P-O-aryl/P-O-alkyl), and combination of amine, secondary amine and imine = NH respectively. These sites in Chlorella groups are mainly responsible for the removal and binding of U(VI) by formation of organic and/or inorganic uranyl phosphates.