Preparation And Flocculation And Adsorption Properties Of The Grafted And Crosslinked Modified Chitosan

In this thesis, with chitosan as the raw material, methacryloyloxyethyl trimethylammonium chloride （DMC） as the monomer, cerium ammonium nitrate as theinitiator and Span-20as the emulsifier, chitosan-DMC graft copolymer wassynthesized through inverse emulsion polymerization. The graft copolymer was thenused as flocculant for treating kaolin suspension. With formaldehyde as thepre-crosslinking agent and glutaraldehyde as the crosslinking agent, crosslinkedchitosan was prepared. The adsorption of Ni²⁺、Cr⁶⁺Pb²⁺by crosslinked chitosan wasstudied. The main findings are as follows:Factors that affect graft copolymerization were discussed, such as reaction time,initiator concentration, chitosan to monomer mass ratio, oil to water volume ratio,reaction temperature, emulsifier concentration. The optimum conditions wereconfirmed by orthogonal experiments: reaction time5h, initiator concentration16mmol/L, chitosan to monomer mass ratio1:6, oil to water volume ratio1:1,reaction temperature60℃, emulsifier concentration4%. Under the optimumconditions the best graft degree reached110%. FTIR spectra showed that DMC wasgrafted onto chitosan.The graft copolymer was then used as flocculant for treating kaolin suspension.Factors that affect flocculation were discussed, such as pH, flocculant dosage andsettling time. The best flocculation effect occurred at pH=6.0, flocculant dosage2.0mg/L and settling time4min. The flocculation effect of chitosan, PAM and the graftcopolymer with different graft degrees was compared and the results showed that theflocculation ability of graft copolymer with high graft degree was better than chitosanand PAM.Factors that affect crosslinking reaction were discussed, such as reaction time,formaldehyde and glutaraldehyde dosage, reaction temperature, oil to water volumeratio, emulsifier concentration. The optimum conditions were confirmed byorthogonal experiments: formaldehyde1mL, reaction time2h, glutaraldehyde2mL,reaction temperature70℃, oil to water volume ratio1:1, emulsifier concentration4%.Under the optimum conditions the adsorption amount for Ni²⁺reached1.98mmol/g.FTIR spectra showed that the crosslinking reaction occurred.The adsorption amount were1.85mmol/g、1.13mmol/g、2.12mmol/g base onNi²⁺、Cr⁶⁺Pb²⁺under25℃, pH=5and the initial concentration of the metal ions were0.01mol/L. The fastest rate of adsorption was Pb²⁺, and then Cr6+, the slowest wasNi²⁺. The adsorption kinetics was in line with pseudo-second kinetic model and theadsorption isotherm followed Freundlich model. The best adsorption ability was atpH=5,4,5for Ni²⁺、Cr⁶⁺Pb²⁺and the regenerative capacity of adsorbent was good.