Sustainable lanthanum-attapulgite/alginate hydrogels with enhanced mechanical strength for selective phosphate scavenging

Abstract

Attapulgite has rarely been used in lanthanum-based alginate hydrogel development for phosphate elimination. The associated research gaps regarding green fabrication, eco-friendly application, and mechanical strength improvement are worthy of systematic investigation. Herein, a newly designed lanthanum-crosslinked attapulgite/sodium alginate (La-ATP/SA) hydrogel adsorbent was prepared by an eco-friendly facile cross-linking method. The results showed that the introduction of attapulgite into sodium alginate enhanced the mechanical strength of La-ATP/SA beads. SEM images, TG tests, and stability assessment tests further verified the reinforced structure. Batch experiments demonstrated that the adsorption information was better described by the Freundlich isotherm equation and the pseudo-second-order kinetic model, harvesting more than 50% phosphate removal of the total amount within 120 min, proving that chemical adsorption dominated the sorption process. The maximum phosphate sorption capacity was 24.57 mg/g and stable phosphate removal was obtained in the presence of the commonly existing anions. The adsorption behavior was pH-dependent and efficient phosphate uptake was maintained over a wide pH range (3–9). The dominant mechanism for phosphate removal of La-ATP/SA was the inner-sphere complex mechanism. Small spherical macromolecular hydrogels can be easily recollected and display good reusability after five cycles. The results of this study demonstrate that the La-ATP/SA hydrogel is a promising sustainable candidate for phosphate control.