Development of polymeric chelating ligands for removal of heavy metals from water
Poly[4-(4-vinylbenzyloxy-2-hydroxybenzaidehyde)i and Po]y[1 -(2-pyridyl)-3-[4- (4-vinyihenzyloxy)phenyl]imidazo( I ,5-a)pyridine-co-methacrylate] were synthesized and characterized and have been evaluated to he effective sorbent materials for [he removal of heavy metals from aqueous solution. Batch adsorption experiments were performed for several divalent metal ions, namely Pb2+, Cd2+. Cu2+, Ni2+, Zn2+ and Co2+. Preliminary batch adsorption screening test revealed that the adsorbents being evaluated had the highest adsorption capacities for Pb and Cd ions, hence they were studied in much greater detail. Upon applying the equilibrium data to the Langmuir and Freundlich isotherm models, the adsorption of the Pb ions on both the polymer and the copolymer fitted well to the Langmuir model. This means that there occurred homogeneous and. complete monolayer coverage of the Ph2+ ions on the polymer surface as well as on the copolymer surface. Two kinetic models, pseudo-first-order and pseudo-second-order were also tested to investigate the adsorption mechanisms and the kinetics was found to be second order and equilibrium adsorption occurred within 15 seconds. This suggests that the adsorption sites are either near the adsorbent or on the adsorbent surface therefore the metal ions have easy access to them thereby resulting in a high frequency of collision between the metal ions and the adsorption sites. The metal removal was also found to be strongly dependent on pH and this is reflected in the gradual increase in percent adsorption as pH increases from 1.0 to 5.5.