Studies on chelating adsorption properties of novel composite material polyethyleneimine/silica gel for heavy-metal ions

Firstly, the coordination processes of line-type polyethyleneimine with Cu2+, Cd2+ and Zn2+ were studied by using visible light absorption spectroscopy and chelation conductivity titration method, and the structures of the chelates were determined. Afterwards, polyethyleneimine (PEI) was grafted onto the surface of silica gel particles via the coupling effect of g-chloropropyl trimethoxysilane (CP), and the novel composite adsorption material PEI/SiO2 with strong adsorption ability towards heavy-metal ions was prepared. The chelating adsorption properties of PEI/ SiO2 for Cu2+, Cd2+ and Zn2+ were researched by both static (batch) and dynamic (flow) methods. The experiment results show that water-soluble polyamine PEI with line-type structure reacts with Cu2+, Cd2+ and Zn2+ easily and quantitatively, and water-soluble chelates with four ligands are formed. The composite material PEI/SiO2 possesses very strong chelating adsorption ability for heavy-metal ions, and the saturated adsorption amount can reach 25.94 mg g 1 and 50.01 mg g 1 for Cu2+ under static and dynamic conditions, respectively. The isothermal adsorption data fit to Langmuir equation, and the adsorption is typical chemical adsorption with monomolecular layer. The adsorbing ability of PEI/SiO2 towards the three kinds of the ions follows the order of Cu2+ > Cd2+ > Zn2+. The pH value has great influence on the sorption, and at pH 6–7, the adsorption capacity is the greatest. The fact that adsorption capacity increases with temperature rising indicates the adsorbing process of PEI/SiO2 for metal ions is endothermic. As diluted hydrochloric acid is used as eluent, the adsorbed heavy-metal ions are eluted easily from PEI/SiO2, and the regeneration and reuse without decreasing sorption for PEI/SiO2 are demonstrated.