The toxicity and mobility of Cr(VI) makes it crucial to decrease the heavy mental from industrial waste streams. To quantitatively elucidate the mechanism of biosorption, Chlorella vulgaris cultivated under five different conditions has been selected for detoxification of Cr(VI) into the less hazardous Cr(III). The application and mechanism for Cr(VI) removal from aqueous solution by C. vulgaris are characterized by FTIR, XPS and EDX analysis, respectively. The results indicate that the -NH2, -COOH are the main functional groups involved in Cr(VI) removal, and the Cr(VI) adsorption increases with the protein content in microalgae biomass. The Cr(VI) anions can be reduced mainly by secondary alcohol groups on biosorbents, and the mechanism for Cr(III) cations binding is quantitatively demonstrated through ion-exchange. The biosorption mechanism under tuned culture conditions has been finally illustrated, which helps point out some guidelines to select the suitable algae biosorbents for Cr(VI) removal. (C) 2013 Elsevier B.V. All rights reserved.