Competitive adsorption of nickel(II) and cadmium(II) ions by chitosan cross-linked with sodium tripolyphosphate
Ataollah Babakhani, Majid Sartaj
Abstract
This study investigates the adsorption of Ni(II) and Cd(II) ions from single and binary metal ion solutions onto chitosan and crosslinked chitosan beads, which was accomplished by an environmentally-friendly crosslinker, sodium tripolyphosphate. The synthesized adsorbents were characterized by swelling test, BET and SEM, and tested for Ni(II) and Cd(II) uptake after optimizing experimental factors, including adsorbent concentration (0.55 g/L) and initial pH (6.5). The single-ion equilibrium adsorption data fitted well by the Langmuir model. In the binary system, a decrease in adsorption capacity was observed, implying the existence of preference in the order of Ni(II) > Cd(II). Among the studied models for competitive adsorption, the extended Freundlich model fitted successfully for the adsorption equilibrium data. Characterization of loaded crosslinked chitosan beads showed amino and phosphate groups were responsible simultaneously for the metal ions uptake. Desorption experiments were also conducted by using a mixture of NaCl and H2SO4, showing acceptable results.