Efficient Removal of Polyvalent Metal Ions (Eu(III) and Th(IV)) from Aqueous Solutions by Polyurea-Crosslinked Alginate Aerogels

Efthalia Georgiou; Ioannis Pashalidis; Grigorios Raptopoulos; Patrina Paraskevopoulou

doi:10.3390/gels8080478

Efficient Removal of Polyvalent Metal Ions (Eu(III) and Th(IV)) from Aqueous Solutions by Polyurea-Crosslinked Alginate Aerogels

Gels. 2022 Jul 29;8(8):478. doi: 10.3390/gels8080478.

Authors

Efthalia Georgiou¹, Ioannis Pashalidis¹, Grigorios Raptopoulos², Patrina Paraskevopoulou²

Affiliations

¹ Laboratory of Radioanalytical and Environmental Chemistry, Department of Chemistry, University of Cyprus, P.O. Box 20537, Cy-1678 Nicosia, Cyprus.
² Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, 15771 Athens, Greece.

Abstract

The removal of polyvalent metal ions Eu(III) and Th(IV) from aqueous solutions using polyurea-crosslinked calcium alginate (X-alginate) aerogels has been investigated by batch-type experiments under ambient conditions and pH 3. The material presents relatively high sorption capacity for Eu(III) (550 g kg^-1) and Th(IV) (211 g kg^-1). The lower sorption capacity for Th(IV) compared to Eu(III) is attributed to the net charge of the dominant species in solution under the given experimental conditions, which is Eu³⁺ for Eu(III), and Th(OH)₂²⁺ and Th(OH)₃⁺ for Th(IV). Generally, the sorption is an endothermic and entropy-driven process, and it follows the Langmuir isotherm model. According to the FTIR spectra, sorption occurs via formation of inner-sphere complexes between the surface functional groups and the f-metal cationic species. The presence of europium and thorium in the adsorbent material was confirmed and quantified with EDS analysis. To the best of our knowledge, this is the first report of an aerogel material used as an adsorbent for Eu(III). Compared to other materials used for the sorption of the specific ions, which are mostly carbon-based, X-alginate aerogels show by far the highest sorption capacity. Regarding Th(IV) uptake, X-alginate aerogels show the highest capacity per volume (27.9 g L^-1) among the aerogels reported in the literature. Both Eu(III) and Th(IV) could be recovered from the beads by 65% and 70%, respectively. Furthermore, Th(VI) could also be quantitatively removed from wastewater, while Eu(III) could be removed by 20%. The above, along with their stability in aqueous environments, make X-alginate aerogels attractive candidates for water treatment and metal recovery applications.

Keywords: Eu(III) sorption; Th(IV) sorption; alginate aerogels; environmental remediation; polymer-crosslinked aerogels; polyurea-crosslinked alginate aerogels; thermodynamic; water decontamination.

Grants and funding

This publication is based upon work from COST Action “Advanced Engineering of aeroGels for Environment and Life Sciences” (AERoGELS, ref. CA18125), supported by COST (European Cooperation in Science and Technology). The General Secretariat for Research and Innovation, Greece, and the Special Account of Research Grants of the National and Kapodistrian University of Athens are also acknowledged.