Abstract
Metal cleaning and plating baths, pulp, paper board mills, printed circuit board and wood pulp production, fertilizer industry etc. are releasing copper into the environment and seriously affecting the quality of drinking water. Even minute quantity of copper (1.3 ppm) in water is detrimental to biota. Therefore, abundantly available poultry and agricultural wastes are tested as adsorbents for the removal of copper leading to sustainable management of wastes and improving the quality of water. Sorption capacities of chitosan-Gallus domesticus eggshell, chitosan-Dromaius novaehollandiae eggshell (CH-GDES, CH-DNES) and chitosan-Dromaius novaehollandiae feather (CH-DNF) composites were first evaluated for copper removal from aqueous solution by ‘one variable at a time’ method, and further experiments were carried out by a three level full factorial design of Response Surface Methodology (RSM). The percent removal of copper by the composites increased with the increase in contact time and the kinetics best fitted to the pseudo - second order model. The optimum pH of the aqueous solution was found to be 6 for the removal of copper for all the three composites. The experimental data of initial metal ion concentration was fitted using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich adsorption isotherm models, and the better suited is Langmuir's isotherm model. Chitosan-Gallus domesticus eggshell composite showed the highest metal uptake potential of copper (qmax 56.49 mg/g). Thermodynamically, copper adsorption onto the bio-composites is inferred as spontaneous, irreversible and endothermic in nature. Characterization of the adsorbents by SEM-EDS, FTIR, XRD and BET, before and after adsorption of copper, revealed that the sorption is due to the mechanisms of chemisorption, ion exchange and/or complexation. The adsorbent pads/filters made of natural renewable biopolymer composites like CH-GDES/CH-DNES/CH-DNF, can be placed at the source to prevent bulk water pollution with copper and maintain the concentration well below the permissible limits in the ground water.
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