Selective adsorption of U(VI) from real mine water using an NH2-functionalized silica packed column

Abstract

The adsorption of U(VI) from natural mine water (i.e. containing Na+, K+, Ca2+, Mg2+ as major cations, and Cl−, SO42− and HCO3− as major anions) was investigated in dynamic mode using packed column containing high-capacity sorbents modified by NH2 organic moieties. The use of packed columns was effective in removing trace amounts of U(VI) species in natural water. The adsorption capacity obtained with amine functionalized SBA-15, a mesostructured silica, was compared with those obtained with commercial cationic exchange resin and grafted commercial silica. Hybrid mesoporous silica and particularly SBA-15, were found to be very effective and selective for U(VI) removal from mine water (C0 ~ 300 ppbU) since 500 mg of adsorbent was able to remove U(VI) species present in 6 L of water. Nevertheless, our results showed that mesostructuration did not play a major role in adsorbent capacity, and that only the amine functional group density was important for the U(VI) aqueous removal. This finding was very important because cheaper commercial silica can be used instead of mesostructured silica such as SBA-15. Furthermore, the role of competitor ions Ca2+ and HCO3−, commonly found in natural waters, was also studied by performing adsorption experiments with synthetic solutions representative of mine waters. Results coupling aqueous speciation modelling and XPS measurements showed that hydrogen carbonate ions had a negative impact for U(VI) species adsorption on amino modified silica. Results however demonstrated that amine-grafted silica could be considered a very promising material for the removal of trace level of uranium from mine water.