Studies on hexavalent chromium biosorption by chemically-treated biomass of Ecklonia sp.

Abstract

The biomass of the brown seaweed, Ecklonia sp., is capable of reducing Cr(VI) to Cr(III). However, very little is known about the mechanism of Cr(VI) reduction by the biomass. The aims of the present investigation were to enhance the Cr(VI)-reducing capacity of the biomass using various chemical treatments and to elucidate the mechanisms governing Cr(VI) reduction. Among the various chemical treatments, acid-treatment showed the best performance with regards the improvement of Cr(VI) removal from the aqueous phase, while organic solvent-treatment significantly improved the removal efficiency of total Cr in the equilibrium state. Based on FTIR study, the biomass was subjected to chemical modification of its amino and carboxyl groups, to examine their roles in the Cr(VI) removal from the aqueous phase. Methylation of the amino group significantly decreased the Cr(VI) removal rate, but amination of the carboxyl group significantly increased the Cr(VI) removal rate. Meanwhile, esterification of the carboxyl group and carboxylation of the amino group decreased the Cr(VI) removal rate, but the former showed a more negative effect than the latter. These findings indicated that the amino and carboxyl groups take part in the Cr(VI) removal from the aqueous phase. In conclusion, mechanisms for direct and indirect Cr(VI) removal are proposed, and some aspects for the application of this biomass to Cr(VI) detoxification are discussed.