Enhanced Pb2+ adsorption using recyclable magnetic sodium alginate in a network structure for high renewable capacity

This study presents the synthesis of a magnetic sodium alginate hydrogel for efficient adsorption of heavy metal ions. The hydrogel, composed of sodium alginate, demonstrates a network structure that facilitates effective metal ion adsorption. Utilizing magnetic forces, the hydrogel can be easily separated and regenerated, exhibiting excellent recyclability. Compared to traditional adsorbents, the magnetic sodium alginate hydrogel shows significantly improved adsorption capacity, particularly for Pb2+ ions. At pH ca. 4 and an adsorption time of 120 min, the hydrogel achieves a maximum adsorption capacity of 137 mg/g for Pb2+, with an adsorption rate of 83 %. The adsorption kinetics follow a pseudo-second-order equation, while thermodynamically, the process adheres to the Freundlich adsorption model, with capacity positively correlated with temperature and concentration. The negative ΔH value indicates an exothermic and spontaneous adsorption process. In competitive adsorption experiments, the hydrogel demonstrates strong selective adsorption towards Pb2+. It also exhibits excellent reusability, maintaining 80 % adsorption capacity after 10 cycles. The magnetic sodium alginate composite material possesses favorable recyclability and convenient magnetic separation properties, offering significant potential in various applications.