Biosorption mechanism of Cr (VI) onto cells of Synechococcus sp.

Abstract

The biosorption mechanism of Cr (VI) ions on Synechococcus sp. biosorbent was studied by analyzing the biosorption kinetics as well as speciation change and bond formation during the biosorption process. The kinetics study shows that the adsorption process of Cr (VI) consists of a very fast stage in the first several minutes, in which more than half of the saturation adsorption is attained, and a slower stage that approximately follows the first order kinetic model, basically Freundlich isotherm models were observed. Comparative studies of FT-IR spectra of K₂Cr₂O₇, free cells of Synechococcus sp., and Cr-bound cells of Synechococcus sp. show that the speciation of chromium that binds to the cells of Synechococcus sp. is Cr (III), instead of Cr (VI), and the carboxylic, alcoholic, amido and amino groups may be involved in the binding of Cr (III). Integrative analyses of the surface electric potential, the effect of pH value on adsorption behavior of Cr (VI), and the results of FT-IR show that the biosorption of Cr (VI) follows two subsequent steps, biosorption of Cr₂O₇²⁻ by electrostatical force at the protonated active sites and reduction of Cr₂O₇²⁻ to Cr³⁺ by the reductive groups on the surface of the biosorbents.

Keywords

biosorption / Synechococcus sp / Cr (VI) / biosorption mechanism / biosorption kinetics