The effect of groundwater composition on uranium(VI) sorption onto bacteriogenic iron oxides.

In this study, we investigated the effect of groundwater composition on the sorption of U(VI) onto bacteriogenic iron oxides (BIOS) and synthetic ferrihydrite (HFO). The concentration of carbonate was found to be the key factor controlling U(VI) sorption onto both BIOS and HFO. However, the efficiency of HFO to adsorb uranium(VI) was higher than that of BIOS at pH 7.0. The pH value also played an important role on the U(VI) sorption onto iron oxides. U(VI) sorption onto BIOS was optimum in the pH range 3-4.5, whereas in the same pH range, the ability of HFO to adsorb U(VI) was very low. HFO was very efficient in adsorbing U(VI) in the pH range 4.5-6.5. Zeta potential measurements have been employed to understand the different removal trends between BIOS and HFO. BIOS had a negative surface charge across the whole pH range examined, in contrast to HFO, which had point of zero charge 7.6. The sorption results have been incorporated in a surface complexation model, which predicted adequately the pH-dependent sorption of U(VI) onto both types of iron oxides.