Red Mud-Sodium Alginate Hydrogels for Synergistic Adsorption of Pb(II), Cd(II), and Cu(II) from Water: Mechanistic Insights

for Pb(II), Cd(II), and Cu(II), respectively, well-described by the Langmuir and PSO models. In multimetal systems, RMSA demonstrated preferential uptake of Pb(II) due to its smaller hydration radius. Importantly, practical application tests validated the robust performance of RMSA in complex real wastewater, achieving an 85.5% removal rate for Pb(II). Furthermore, TCLP tests confirmed the absolute environmental safety of the spent hydrogel with a negligible leaching rate (<0.03%), effectively reducing secondary pollution risks. Combined with its moderate reusability over five regeneration cycles and a production cost that is 67.5% lower than that of commercial alternatives, RMSA represents a sustainable and cost-effective strategy for using waste to treat waste in practical wastewater purification and agricultural water management.