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Removal of Trivalent and Hexavalent Chromium by Seaweed Biosorbent

David Kratochvil, Patricia Pimentel,^† and Bohumil Volesky*

Department of Chemical Engineering, McGill University, 3610 University Street, Montreal, Canada H3A 2B2

Environ. Sci. Technol., 1998, 32 (18), pp 2693–2698

DOI: 10.1021/es971073u

Publication Date (Web): August 13, 1998

†

CETEC, Belo Horizonte, MG, Brazil.

Author to whom correspondence should be addressed. E-mail: boya@chemeng.lan.mcgill.ca.

Abstract

Protonated or Ca-form Sargassum seaweed biomass bound up to 40 mg/g of Cr(III) by ion exchange at pH 4. An ion-exchange model assuming that the only species taken up by the biomass was Cr(OH)²⁺ successfully fitted the experimental biosorption data for Cr(III). The maximum uptake of Cr(VI) by protonated Sargassum biomass at pH 2 was explained by simultaneous anion exchange and Cr(VI) to Cr(III) reduction. At pH <2.0, the reduction of Cr(VI) to Cr(III) dominated the equilibrium behavior of the batch systems, which was explained by the dependence of the reduction potential of HCrO₄^- ions on the pH. At pH >2.0, the removal of Cr(VI) was linked to the depletion of protons in equilibrium batch systems via an anion-exchange reaction. The optimum pH for Cr(VI) removal by sorption lies in the region where the two mechanisms overlap, which for Sargassum biomass is in the vicinity of pH 2. The existence of the optimum pH for the removal of Cr(VI) may be explained by taking into account (a) the desorption of Cr(III) from biomass at low pH and (b) the effect of pH on the reduction potential of Cr(VI) in aqueous solutions. Seventy percent of Cr(VI) bound to the seaweed at pH 2 can be desorbed with 0.2 M H₂SO₄ via reduction to Cr(III).

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