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

Abstract

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 = 318 K were about 190.95 mg/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 0.05 M HNO₃, which indicated that PS-EDTA/P resin was a promising candidate for removing Pb²⁺ from wastewater.

Keywords:

• Phosphoric acid-modified
• PS-EDTA resin
• Pb²⁺ ions
• Adsorption
• Mechanisms

Acknowledgements

The authors gratefully acknowledge the financial support from the National Major Specific Program of Science and Technology on Controlling and Administering of Water’s pollution (2009ZX07212-001-04), Fundamental Research Funds for the Central Universities (lzujbky-2012-80) and postdoctoral foundation of Lanzhou University.