Crosslinking Agents as Precursors for Improved Selectivity and Adsorption Performance of Alginate Hydrogels Toward Critical Raw Materials

Abstract

Ionically crosslinked alginate hydrogels have a wide range of applications across various fields due to their unique properties, such as biocompatibility, biodegradability, and tunable mechanical properties. Some key applications include biomedical, the food industry, cosmetics, agriculture, biotechnology, and environmental applications. Alginates are frequently crosslinked via the ionic interaction of their carboxyl groups with multivalent anions like Ca2+. In this work, the cross-linked alginate hydrogel was obtained by the ionotropic gelation crosslinking method with Ca2+, Zn2+, Fe3+, and Al3+ ions. The adsorption performance of La3+ and Ho3+ ions on alginate crosslinked hydrogel materials was compared using pH, shaking time, concentration, and temperature. Some kinetic, equilibrium, and thermodynamic equations and hydrogel surface characterization were used to describe the adsorption behavior of La3+ and Ho3+. The adsorption of La3+ and Ho3+ by alginate crosslinked with Zn2+ or Ca2+ ions was the fastest and had a noticeable adsorption capacity, with higher adsorption capacities than alginate crosslinked with Fe3+ or Al3+ ions. Alginate hydrogel materials (ALG@X) were sorted according to the increasing affinities for La3+ and Ho3+ ions: ALG@Zn (214.71 mgLa3+/g, 240.12 mgHo3+/g) > ALG@Ca (172.29 mgLa3+/g, 202.13 mgHo3+/g) > ALG@Al (108.63 mgLa3+/g, 114.10 mgHo3+/g) > ALG@Fe (28.73 mgLa3+/g, 20.29 mgHo3+/g). The real-life environmental application of the alginate hydrogels was performed on Ni-MH battery leachates studying the selectivity of synthesized materials.

Keywords: ionic crosslinking, alginate hydrogels, selectivity, leachates, waste recovery