Selective Adsorption of La3+ Using a Tough Alginate-Clay-Poly(n-isopropylacrylamide) Hydrogel with Hierarchical Pores and Reversible Re-Deswelling/Swelling Cycles

Rare earth elements are an important strategic resource, and it is urgent that the rare earth industry continue to explore and develop novel separation methods and technologies. Herein, we fabricated an efficient semi-IPN alginate-clay-poly(n-isopropylacrylamide) (NIPAm) hydrogel by a frozen polymerization method with the help of UV light irradiation, where alginate was employed as the main adsorption functional compound. The as-prepared hydrogel exhibits tough, sponge-like hierarchical macroporous and reversible temperature-responsive characteristics. The maximum adsorption capacity of La3+ is 182 mg/g for the hydrogel composition of 5.0% NIPAm, 4.0% clay, and 3.0% alginate. The Langmuir isotherm fits the data very well, and the adsorption follows the pseudo-second-kinetic equation. The trace of La3+ ions can be effectively separated from the coexisting metal ions. After six repeated adsorption–desorption cycles, no obvious deformation of the shape and or loss of adsorption capacity of the bulk hydrogel ...