Analysis and comparative study of preparation, mechanisms, and application of sodium alginate-based composite materials for highly efficient removal of cadmium cations

This study successfully prepared three types of composite gelled beads blended with modified biochar: Sodium alginate/thiol-modified lotus seedpod biochar/CaCO 3 @polyvinyl alcohol (SA/LBS/PF@PVA), Sodium alginate/thiol-modified lotus seedpod biochar/CaCO 3 @chitosan (SA/LBS/PF@CTS), and Sodium alginate/thiol-modified lotus seedpod biochar/CaCO 3 @carboxymethyl cellulose (SA/LBS/PF@CMC). Their maximum Cd 2+ adsorption capacities reached 138.73 mg/g, 64.42 mg/g, and 64.90 mg/g, respectively. These gelled beads exhibited an excellent three-dimensional network structure, particularly SA/LBS/PF@PVA, which displayed outstanding swelling properties. FTIR, XPS, and batch experiments confirmed that the primary adsorption mechanisms for SA/LBS/PF@PVA and SA/LBS/PF@CTS were ion exchange and chelation, whereas SA/LBS/PF@CMC primarily relied on ion exchange, electrostatic interaction and complexation. The adsorption of SA/LBS/PF@PVA and SA/LBS/PF@CMC followed the Freundlich model, while SA/LBS/PF@CTS adhered to the Langmuir model. After five adsorption-desorption cycles, the adsorption capacities of SA/LBS/PF@PVA, SA/LBS/PF@CTS, and SA/LBS/PF@CMC remained relatively stable but lost 26.0%, 17.9%, and 29.2% of their mass, respectively. In fixed-bed column experiments, 2 g of SA/LBS/PF@PVA, SA/LBS/PF@CTS, and SA/LBS/PF@CMC achieved Cd 2+ removal capacities of 113.83 mg/g, 53.75 mg/g, and 87.65 mg/g, respectively, with column efficiencies of 43.94%, 31.12%, and 58.65%. This study highlights the significant impact of the components and ratios of sodium alginate-based composite gelled beads on their adsorption characteristics, indicating that optimizing the formulation and improving mechanical properties can enhance their practical application effectiveness.