Study of the mechanisms of cadmium biosorption by dealginated seaweed waste.
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 x 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.
Romero-Gonzalez
M E
ME
Division of Chemistry, School of Science and Mathematics, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, U.K.
Williams
C J
CJ
Gardiner
P H
PH
D000327:Adsorption; D002104:Cadmium / Q000737:chemistry / Q000493:pharmacokinetics*; D002245:Carbon Dioxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007474:Ion Exchange; D012037:Refuse Disposal; D012624:Seaweed / Q000737:chemistry*; D014876:Water Pollution / Q000517:prevention & control*
D002104:Cadmium; D002245:Carbon Dioxide; C041069:carboxyl radical