Studies on Cr(VI), Pb(II) and Cu(II) adsorption-desorption using calcium alginate as biopolymer

The aim of this study was to investigate the Cr(VI), Pb(II) and Cu(II) biosorption potential of calcium alginate from aqueous solution and to screen a variety of desorbing agents, in order to access the efficiency of desorption and regeneration of the biosorbent in multiple sorption-desorption cycles. Calcium alginate beads was found to remove heavy metal ions efficiently from aqueous solution with selectivity in the order of Cr(VI)> Cu(II)> Pb(II).The biosorption of metal ions by calcium alginate beads decreased as the initial concentration of metal ions increased in the medium. The maximum heavy metal ions adsorbed was found to be 238,154,120 mg/g calcium alginate beads for Cr(VI), Cu(II) and Pb(II) respectively. The maximum uptake of metal ions was obtained at pH 2.0. Above pH 2.0, biosorption of metal ions by calcium alginate beads was found to be relatively constant for Pb(II) and Cu(II) ions, biosorption of Cr(VI) still increased upto pH 3.0 having 86% removal efficiency. At temperature 35 degrees C, the biosorption of metal ions was found to be highest, with increase or decrease in temperature resulted in a decrease in the metal ions uptake capacity. The sorption data of all three metal ions conformed well the Langmuir isotherm. The bound metal ions could be eluted successfully using 0.1 M EDTA. The successive sorption-desorption studies employing calcium alginate beads indicated that the beads could be regenerated without showing the significant loss in adsorption capacity even after second cycle of adsorption-desorption. The results suggest that calcium alginate beads can be used as a biosorbent for an efficient removal of heavy metal ions from aqueous solution.