Removal of hexavalent chromium from aqueous solution by barium ion cross-linked alginate beads

Abstract

Barium ion cross-linked alginate beads have shown great affinity to toxic hexavalent chromium ions in aqueous solution, in contrast to the traditionally used cal- cium alginate beads. Our adsorption experiments were carried out by the batch contact method. The optimal pH for removal was found to be pH 4. The equilibrium was established in 4 h, and the removal efficiency of chro- mium(VI) was found to be 95 %. The adsorption data were applied to Langmuir, Freundlich, Dubinin-Redushkevich (D-R), and Temkin isotherm equations. Both Langmuir and Freundlich isotherm constants indicated a favorable adsorption. The value of mean sorption energy calculated from D-R isoterm indicates that the adsorption is essen- tially physical. The high maximum chromium(VI) adsorption capacity was determined from the Langmuir isotherm as 36.5 mg/g dry alginate beads. The chro- mium(VI) adsorption data were analyzed using several kinetic models such as the pseudo-first-order, pseudo-sec- ond-order, intraparticle diffusion, and Elovich models, and the rate constants were quantified. Our study suggests that barium alginate beads can be used as cost-effective and efficient adsorbents for the removal of chromium(VI) from contaminated waters.