Study of the mechanisms of cadmium biosorption by dealginated seaweed waste

ROMERO-GONZALEZ, M. E., WILLIAMS, C. J. and GARDINER, P. H. E. (2001). Study of the mechanisms of cadmium biosorption by dealginated seaweed waste. Environmental Science and Technology, 35 (14), p. 3025.

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The ability of dealginated seaweed waste, a waste material derived from the commercial processing of seaweed for alginate production, to remove cadmium from solution was determined. Cadmium sorption was found to be rapid (91% removal within 5 min), achieving a residual concentration of 0.8 mg L-1 after 1-h contact time from an initial solution concentration of 10 mg L-1. The binding of cadmium by dealginate was found to be pH dependent, optimal sorption occurring at around pH 6-8. The mechanism of cadmium ion binding by dealginate was investigated by a number of techniques. Potentiometric titration of the dealginate revealed two distinct pKa values, the first having a value similar to carboxyl groups and the second comparable with that of saturated thiols and amines. Esterification of the dealginate resulted in the subsequent reduction in cadmium sorption (95% to 17%), indicating that carboxyl groups are largely responsible for sorption. Evidence from FT-IR spectra confirmed the presence of carboxyl groups in untreated dealginate, while the number of carboxyl groups was markedly reduced in the esterified sample. Furthermore, the FT-IR spectrum for dealginate was found to be similar to that previously reported for mannuronic acid-rich calcium alginate. Determination of a molar ratio in the displacement of calcium by cadmium on dealginate further supported the presence of an ion-exchange relationship. The ion-exchange constant was calculated to be 0.329 × 10-6. The speciation of cadmium in solution both before and after sorption was determined by an ion-selective electrode (ISE) technique. The findings of this study suggest that the sorption of cadmium by dealginate is mainly due to an ion-exchange mechanism.

Item Type: Article
Research Institute, Centre or Group - Does NOT include content added after October 2018: Biomedical Research Centre
Identification Number:
Page Range: p. 3025
Depositing User: Ann Betterton
Date Deposited: 25 Feb 2008
Last Modified: 18 Mar 2021 21:45

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