Waste calcite sludge as an adsorbent for the removal of cadmium, copper, lead, and zinc from aqueous solutions

Sludge residues, an industrial waste material for the removal of cadmium (Cd2+), copper (Cu2+), lead (Pb2+), and zinc (Zn2+) from aqueous solutions were investigated using batch method. Batch mode experiments were carried out as a function of solution pH, adsorbent dosage, initial concentration, and contact time. The results indicated that the adsorbent showed good sorption potential and maximum metal removal was observed at pH a parts per thousand yen 3. Within 120 min of operation, about 63.7, 95.2, 99.9, and 88.2% of Cd2+, Cu2+, Pb2+, and Zn2+ ions were removed from the solutions, respectively. Sorption curves were well fitted to the Langmuir and Freundlich models. The adsorption capacities for Cd2+, Cu2+, Pb2+, and Zn2+ ions at optimum conditions were 121.2, 1067.8, 566.4, and 534.2 mg g(-1), respectively. The kinetics of Cd2+, Cu2+, Pb2+, and Zn2+ adsorption from aqueous solutions was analyzed by fitting the experimental data to pseudo-first- and pseudo-second-order kinetic models. However, the pseudo-first-order kinetics model provided much better R (2) values and the rate constant was found to be 0.001 min(-1) for Cd2+, Cu2+, Pb2+, and Zn2+ ions. The results revealed that sludge residues can adsorb considerable amount of Cd2+, Cu2+, Pb2+, and Zn2+ ions and it could be an economical method for the removal of these ions from aqueous systems.