Uranium removal from contaminated groundwater using goethite-loaded composite microporous membrane

In this study, we have coupled adsorption and membrane separation for the removal of uranium from contaminated groundwater in environmentally relevant conditions at low energy requirements. The study mainly focuses on elucidating uranium [U(VI)] adsorption mechanisms using surface complexation modeling approach in a novel goethite-loaded composite microfiltration membrane (GLM). The experiments involved immobilizing goethite nanorods in a microporous (0.22 μm pore size) poly (vinylidene fluoride) (PVDF) membrane. The effect of varying goethite loading and hydraulic residence time on U(VI) removal was investigated at field-relevant pH (i.e. pH 8.5). U(VI) adsorption (i.e. 4.95 μg·mg^-1) was optimum at a goethite loading of 1.20 mg·cm^-2. The effect of varying hydraulic residence time had no impact on U(VI) removal which was also confirmed via performing batch adsorption kinetic experiments. GLM membrane loaded at 1.2 mg·cm^-2 could treat 275 L of U(VI) contaminated water having 200 μg of U L^-1 below WHO drinking water limit (i.e. 30 μg of U L^-1) with 1 m² of membrane surface area at a maximum adsorption capacity of 6.12 μg·mg^-1. Varying the pH of aqueous solution, containing U(VI) from pH 4.0 to pH 10.0, showed a significant impact on uranium uptake ranging from 0.7 μg·mg^-1 to 2.63 μg·mg^-1 by the composite membrane. The adsorption mechanism of uranium onto goethite was explained via the formation of bidentate surface complexes using the Surface Complexation Model (SCM). The results of batch pH edge experiments and SCM have been compared with pH experiments performed using GLM. The results of SCM predicted the batch pH edge experiment within a RMSE of 0.055. The trend of U(VI) removal in membrane experiments was observed to be similar to that of batch pH edge experiments and was well predicted by the SCM model. Our results show that the novel goethite-loaded membrane has the potential for effective removal of uranium with a lower specific energy consumption.