Characterization of natural biosorbents used for the depollution of waste water

Many crustaceans and arthropods contain chitin as an integral part of cell wall structure. It is a linear polyaminosaccharid composed of B(1--->4)-2-acetamino-2-deoxy-D glucose units bound by glycoside bonds. The objective of this work was to carry out a physical and a chemical characterization of raw chitin from different origins (shrimps, crabs and lobsters) used for removing heavy metals from waste water. The adsorption percentages for the investigated concentrations of raw chitin (1 g/l) and metals (10-100) mg/l reached the following maximum values : Pb2+ (95%), Cd2+ (90%), Cu2+ (89%) and Zn2+ (82%). The adsorption study was described using the Freundlich equation in its linear form. Adsorption kinetics showed that raw chitin needs a few minutes to adsorb a maximal quantity of heavy metal, with more than 50 % of the Cd2+, Cu2+, Zn2+ and 90 % of the Pb2+ being adsorbed in 10 minutes. Physical and chemical characterization of the interactions between metals and chitin in solution showed the importance of the mineral fraction of raw chitin in the retention of heavy metals by cationic exchange.