Isolation of an efficient biosorbent of radionuclides (226Ra, 238U): green algae from high-background radiation areas in Iran

In this study, 26 Cyanophyta and Chlorophyta microalgae were isolated from high-background radiation areas in Iran. Among them, one green alga showed the highest radionuclide sorption capacity. This uranium- and radium-resistant microalga belongs to the genus Graesiella, and based on its morphological and molecular characteristics, it was identified as Graesiella emersonii Shihira and R.W. Krauss. The sample was isolated from the Ab-e-Siah hot spring in Ramsar (a city in northern Iran) with a Ra-226 content of 130 Bq L-1. This strain exhibited maximum sorption capacities of 69 kBq g(-1) of Ra-226 and 530 mg g(-1) of U-238. The optimum conditions for removal of the radionuclides were determined, and the results showed that the pH and initial cell concentration significantly affected radionuclide sorption. Furthermore, the experimental data were well-fitted to the Langmuir isotherm and pseudo-second-order kinetic models. FT-IR spectra and SEM analyses showed the mechanisms of the sorption process. The results of the present study indicated that the green alga G. emersonii, can serve as an appropriate candidate for designing an efficient sorption system for an area contaminated by Ra-226 and U-238 radionuclides.