Chitosan selectivity to remove cadmium (II), cupper (II) and lead (II) from aqueous phase: PH and organic matter effects
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abstract
The objective of this study was to investigate the selectivity of a chitosan, produced by a biological method from shrimp wastes (Litopenaeus sp.), for cadmium, cupper and lead in presence of natural organic matter at different solution pHs. The desorption grade of cadmium from saturated biosorbent was also investigated. Adsorption isotherms, of one and three adsobates, were conducted in batch reactors at pH 4, 5 and 7 and 25°C at an initial metal concentration of 5 to 100 mg/L. The chitosan utilized in this research has a molecular weight of 107.8 kDa and a degree of acetylation of 33.7%25, and the clarified water used as solvent contained 10.7 mg/L of total organic carbon. On the other hand, desorption experiments were conducted in acidic conditions. The results obtained in this study revealed that chitosan has a higher sorption capacity for copper follow by lead and cadmium, and hence, the biosorbent selectivity was as follows Cu>Pb-Cd. 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 %25 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.
