CHARACTERIZATION OF ACETONE-WASHED YEAST BIOMASS FUNCTIONAL-GROUPS INVOLVED IN LEAD BIOSORPTION

The mechanism of lead cation biosorption by acetone-washed biomass of Saccharomyces uvarum was investigated by chemical modifications and sp ectroscopic monitoring of the cell components. Reacting the carboxyl g roups with propylamine, which neutralizes these anions, considerably d ecreased the metallic ion uptake, indicating that negatively charged c arboxyl groups play an important role in lead biosorption due to elect rostatic attraction. After lead biosorption the photoacoustic Fourier transform infrared spectroscopy showed a change in the symmetrical str etch of the carboxylate groups of the acetone-washed yeast biomass, an d the X-ray photoelectron spectroscopy oxygen peak was also found to b e shifted. These findings support the hypothesis that lead uptake occu rs mainly through binding to the carboxyl group. In X-ray photoelectro n spectroscopy the nitrogen peak decreased after the biosorption of le ad, suggesting that nitrogen-containing groups are also involved in th e biosorption process. Acylation of amino groups was shown to increase the lead biosorption capacity. The acylation reaction converts the po sitively charged amino group to an amide capable of coordination to le ad cations. Deproteination by boiling the biosorbent with NaOH increas ed the lead uptake. The acetone-washed biomass uptake of lead from an aqueous solution at pH 5.5 was 48.9 mg/g dry weight. Pure chitin adsor bed 48.8 mg lead/g dry weight. Mannan isolated from S. uvarum did not adsorb lead at all. Electrostatic attraction of the carboxyl groups an d other anions present in the acetone-washed biomass, and complexation with nitrogen atoms, especially in chitin, appear to be the main mech anisms involved in lead cation biosorption. (C) 1997 John Wiley & Sons , Inc.