ADSORPTION OF Pb2+ AND Cd2+ ON CHITOSAN/CARBOXYMETHYLCELLULOSE POLYELECTROLYTE COMPLEXES

Besides the rapid development of the modern industry, heavy metals and other pollutants has become a serious threat to the availability of drinking water, so wastewater treatment is nowadays one of the main concerns of food, textile, metallurgic and petroleum industries, among many others. Considering their chronic toxicity and low biodegradability, improperly disposed heavy metals represent a serious hazard to the environment and ecosystems, requiring effective and economically viable technologies to adequately remove them from industrial effluents. Among the methods for their removal from wastewater, adsorption still attract great attention due to its high efficiency, affordable costs, as well as relative ease of operation. In the present study, we assessed the applicability of macroscopic polyelectrolyte complexes formed by chitosan (CHS) and carboxymethylcellulose (CMC), here called CHS/CMC macro-PECs, as a novel and ecologically harmless adsorbent for Pb2+ and Cd2+, two heavy metal cations often present in industrial wastewaters. Briefly, at room temperature (25.0 ± 1.0 ◦C), appropriate volumes of CMC dispersions were added dropwise to a previously prepared CHS dispersion, under continuous magnetic stirring. The CHS:CMC mixing ratio 1:3 and pH 3.0 were used, based on previous optimization results obtained by our team. The formed CHS/CMC macro-PECs were frozen, grinded, lyophilized, and then used in batch adsorption experiments. The optimum adsorption pH values, at 25 ºC, were 10.0 for Cd2+ and 9.0 for Pb2+. Kinetics assays indicated that the pseudo second order model was the best to represent the adsorption kinetics of Cd2+, whereas pseudo first order was the most suitable for Pb2+ adsorption. Also, the Langmuir, Freundlich and Redlich-Peterson isotherms’ models were fitted to experimental data, with the Langmuir model providing the best fit. The maximum adsorption (qmáx) values of CHS/CMC macro-PECs in the adsorption of Cd2+ and Pb2+ were 75.43 and 74.42 mg/g, respectively (corresponding to 98.46% and 97.14%). These results not only bring an accurate quantitative characterization of the adsorption of two important pollutants on CHS/CMC macro-PECs, but also demonstrate a novel technological applicability (water decontamination) for two inexpensive, easy-to-obtain food polysaccharides (CHS and CMC).