Extremely Efficient Uranium Removal from Aqueous Environments with Polyurea-Cross-Linked Alginate Aerogel Beads

The removal of uranium(VI) from laboratory and environmental waters using polyurea-cross-linked calcium alginate (X-alginate) aerogels has been investigated by means of batch-type experiments. The experimental data revealed that the material presents extremely high adsorption capacity for uranium(VI) (up to 2023 g kg–1 of aerogel). The adsorption process is endothermic, entropy-driven, and follows the Langmuir isotherm model. The Fourier transform infrared spectroscopy (FTIR) data corroborate the results of the batch experiments and indicate that adsorption occurs via the formation of inner-sphere complexes between the surface functional groups of X-alginate beads and UO22+. The post-adsorption presence of uranium in the adsorbent was confirmed and quantified with energy-dispersive X-ray spectra (EDS) analysis. Compared to other aerogel adsorbents of UO22+ from the literature, X-alginate aerogels show one of the highest sorption capacities per weight and the highest per volume. Uranium could be recovered almost quantitatively (∼100%) in aqueous solutions of Na2CO3 (pH 11) or ethylenediaminetetraacetic acid (EDTA) (pH 10). The aerogel material has been effectively applied for the removal of uranium(VI) from acid mine drainage (AMD), groundwater, and seawater samples. It should be noted that X-alginate aerogel beads are stable in all of the above environments (i.e., no swelling, shrinking, or disintegration was observed). The extraordinary adsorption capacity, even in the presence of competing metal cations, and the stability of X-alginate aerogel beads in environmental waters render them excellent candidates for the specific application.