(320i) Chitosan Selectivity to Remove Cadmium (II), Copper (II) and Lead (II) from Aqueous Phase: pH and Organic Matter Effects

Wastewaters from metal-mechanic industry, agriculture wring outs, municipalities, etc. pollute surface waters and aquifers with toxic metals, such as copper, cadmium and lead, which drastically affect the aquatic and terrestrial life. The use of biosorbents, like chitin and its subproduct chitosan, to remove toxic compounds from water has reported acceptable results that have encouraged to optimize the production process and to improve the quality of these types of biosorbents. The objective of this study was to investigate the selectivity of a chitosan, produced by biological method from shrimp wastes (Litopenaeus sp.), for cadmium, copper and lead in presence of natural organic matter at different solution pHs. And also to determine the desorption grade of contaminants once the biosorbent was saturated. The adsorption isotherms were conducted in batch reactors at pH 4, 5 and 7 and 25 oC, at 5 to 100 mg/L initial metal concentrations. The clarified water utilized in these experiments contained 10.7 mg/L of TOC (total organic carbon) and was collected from a local water treatment plant (los filtros ? SLP). The chitosan used in this research has a molecular weight of 107.8 kDa and degree of acetylation of 33.7%. The TOC concentration in both water and chitosan, before and after it was contacted with clarified water, was determined by a Shimadzu 5000A TOC analyzer. Results obtained in this study revealed that chitosan has a higher sorption capacity for copper follow by cadmium and lead, and hence, the biosorbent selectivity was as follows Cu>Cd>Pb. This happened in both deonized and clarified water at pH 4. It was also found that cadmium removal by chitosan increased as pH rise from 4 to 7; 0.5, 3.3, and 6.0 mg/g for pH 4, 5 and 7, respectively, at an equilibrium concentration of 20 mg/L. On the other hand, experiments carried out in clarified water showed that the cadmium sorption capacity of chitosan was enhanced by the presence of natural organic matter; 6.7 mg/g in deinozed water and 19.9 mg/g in clarified water at an equilibrium concentration of 50 mg/L and pH 7. Finally, the preliminary desorption experiments conducted at pH 2 and 3, with HNO3, reported 68 and 44.8% of metal desorbed, accordingly. These findings reveal that the chitosan tested in this study posses an acceptable sorption capacity for cadmium, copper and lead. It was found that this biosorbent is more selective for cupper follow by lead and cadmium, and that the cadmium sorption capacity increases as pH rises. It was also observed that the natural organic matter enhances the chitosan sorption capacity, and that the cadmium adsorption is partially reversible at acid pHs.