Enhanced removal of Pb2+ from water by adsorption onto phosphoric acid-modified PS-EDTA resin: mechanism and kinetic study

The present study aimed to analyze the behavior of phosphoric acid-modified PS-EDTA resin (PS-EDTA/P resin), in the adsorption and removal of Pb2+ ions from an aqueous solution in order to identify the parameters that determine this process. The effects of solution pH, initial metal concentration, temperature, contact time, ionic strength, and competing ions on Pb2+ sorption were investigated in batch experiments. The results indicated that Pb2+ sorption on PS-EDTA/P resin was strongly dependent on pH and weakly dependent on ionic strength. The abundant phosphorus-containing functional groups on the surfaces of PS-EDTA/P resin played an important role in Pb2+ sorption. The presence of Hg2+, Zn2+, Cu2+, and Cd2+ reduced the Pb2+ sorption slightly on PS-EDTA/P resin. The maximum sorption capacities (Q(max)) of Pb2+ sorption on PS-EDTA/P resin at pH 6.0 and T=318K were about 190.95mg/g, higher than PS-EDTA resin. Studies on adsorption mechanism revealed that surface adsorption and intraparticle diffusion were involved in the adsorption of Pb2+ on PS-EDTA/P resin. It was concluded that the adsorption mechanism could be the specific reaction between Pb2+ and the functional groups on the surface of PS-EDTA/P resin which forms inner-sphere complexation. The thermodynamic parameters calculated from temperature-dependent sorption isotherms suggested that Pb2+ sorption on PS-EDTA/P resin was spontaneous and endothermic in nature. The Pb2+ adsorbed on PS-EDTA/P resin could be desorbed effectively by 0.05M HNO3, which indicated that PS-EDTA/P resin was a promising candidate for removing Pb2+ from wastewater.