Adsorption Properties Of Chitosan Composite Adsorbent For Heavy Metals

In this thesis, the cross-linked chitosan with metal ions template and chitosan-bentonite composite materials were synthesized on the base of the characteristics of chitosan and bentonite. Their adsorption capacities for Pb(â…¡) and Nd(â…¢) were investigated. The results are as follows.The optimum conditions of preparation the cross-linked chitosan with metal ions template adsorbent are that the mass ratio of chitosan and Pb(â…¡) is 1:0.094, complex reaction time is 7h, the dosage of crosslinking agent glutaraldehyde is 6mL and the crosslinking time is 16h; the mass ratio of chitosan and Nd(â…¢) is 1:0.10, complex reaction time is 7h, the dosage of crosslinking agent glutaraldehyde is 6mL and the crosslinking time is 16h. The optimum conditions of preparation the composite adsorbent is that the mass ratio of chitosan with DS of 0.95 and bentonite is 1:25.The template cross-linked polymers with metal ions have overcomed the shortcoming of chitosan dissolved in acidic conditions. When the pH is near neutral, the adsorption capacities of the template cross-linked polymer for Pb(â…¡) and Nd(â…¢) are 58.23mg/g and 41.09mg/g reaching the maximum. The optimum pH of adsorption for Pb(â…¡) and Nd(â…¢) by the chitosan-bentonite composite material is 7, the adsorption capacities are around 76.75mg/g and 91.71mg/g. The adsorption of the cross-linked with chitosan metal ions template for Pb(â…¡) and Nd(â…¢) reach adsorption equilibrium after 18h and 2h. However, the chitosan-bentonite composite materials take 2h and 30min to reach adsorption equilibrium to adsorb for Pb and Nd ions.The isotherms of the adsorption of the two kinds of composite adsorbents are according to the Freundlich isotherm formula and the adsorption belong to the heterogeneous multi-molecular layer adsorption. the adsorption kinetics of the adsorption are according to Lagergren secondary adsorption kinetic model.The infrared analysis indicates that part of the activated amino group of the cross-linked chitosan with template chelated with the metal ions, hydroxyl and amino group take cross-linking reaction with glutaraldehyde. X-ray diffraction analysis shows that the d001 of bentonite composite with chitosan increases only 0.04 nm, which accounts for that the layer distance of bentonite increases little by the accession of chitosan. The cross-linked chitosan with metal ions template and the chitosan-bentonite composite materials both have good adsorption capacity. The chitosan-bentonite composite materials not only have faster absorption rate, higher adsorption capacity, but also have more simple synthesis technology, lower production costs.