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

摘要

Sludge residues, an industrial waste material for the removal of cadmium (Cd~(2+)), copper (Cu~(2+)), lead (Pb~(2+)), and zinc (Zn~(2+)) 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 ≥ 3. Within 120 min of operation, about 63.7, 95.2, 99.9, and 88.2% of Cd~(2+), Cu~(2+), Pb~(2+), and Zn~(2+) ions were removed from the solutions, respectively. Sorption curves were well fitted to the Langmuir and Freundlich models. The adsorption capacities for Cd~(2+), Cu~(2+), Pb~(2+), and Zn~(2+) ions at optimum conditions were 121.2, 1067.8, 566.4, and 534.2 mg g~(-1), respectively. The kinetics of Cd~(2+), Cu~(2+), Pb~(2+), and Zn~(2+) 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 Cd~(2+), Cu~(2+), Pb~(2+), and Zn~(2+) ions. The results revealed that sludge residues can adsorb considerable amount of Cd~(2+), Cu~(2+), Pb~(2+), and Zn~(2+) ions and it could be an economical method for the removal of these ions from aqueous systems.