Calcium phytate cross-linked polysaccharide hydrogels for selective removal of U(VI) from tailings wastewater.

Efficient uranium capture from rare earth tailings wastewater holds great importance for human health and sustainable development. Herein, we present a simple and eco-friendly approach to form a single network hydrogel through electrostatic interaction between chitosan and sodium alginate. Subsequently, calcium phytate is introduced as a natural crosslinking agent to generate a secondary cross-linked network, leading to a composite hydrogel (CS-SA/PCa) with a doubly enhanced network structure for efficient adsorption of uranium from wastewater. The established multistage porous structure enables the rapid diffusion of uranyl ions, and the abundant phosphate groups serving as adsorption sites can offer high affinity for U(VI). Most importantly, CS-SA/PCa is formed through physical cross-linking of sustainable biopolymers, avoiding the use of toxic chemical agents. In addition, CS-SA/PCa exhibited significantly better mechanical properties than those of single-network physical hydrogels crosslinked by electrostatic interactions, which overcame the weak mechanical properties of physical hydrogels. It provides a new method for the manufacture of environmentally friendly, low-cost and robust physical hydrogels based on natural polymers.