Biosorption of Pb2+ and Zn2+ by Ca-alginate immobilized and free extracellular polysaccharides produced by Leuconostoc citreum B-2

Heavy metal pollution seriously threatens human health and ecological environment. Due to high efficiency and excellent development prospect, adsorption technology has attracted worldwide attention. It is significant to develop renewable adsorbents with excellent adsorption performance.In this study, the Pb2+ and Zn2+ adsorption capacity of Ca-alginate immobilized and free (without immobilization) Leu. citreum B-2 extracellular polysaccharides (EPS) was investigated. Isotherm and kinetic models were used to evaluate the adsorption performance. The adsorbents were characterized by SEM, FT-IR and XPS spectroscopy.The maximum biosorption of Pb2+ 269.54 and Zn2+ 49.88 mg/g was achieved with immobilized EPS. Thermodynamic studies showed that the adsorption of Pb2+ and Zn2+ on EPS was a spontaneous and feasible process, and the adsorption properties of EPS were exothermic for lead and endothermic for zinc. All the adsorption processes conformed to the pseudo-second-order model and Langmuir adsorption isotherm model, indicating that the adsorption was mainly chemisorption taken placed on single adsorption surface. SEM results showed that the surface of EPS become denser after adsorption. FTIR and XPS analysis indicated that the adsorption mechanism mainly involved the complexation reaction and ion exchange of functional groups such as CO, O-C-O, -COOH and C-OH.