Synthesis And Modification Of Magnetic Chitosan And Application To Selective Separation Of Heavy Metal Ion

Magnetic chitosan beads were prepared by cross-linking Fe₃O₄ and chitosan with glutaraldehyde. Then magnetic amination chitosan beads were synthesized with diethylenetriamine. The products were used to study the adsorption capacity for various of heavy metal ions, such as Cu²⁺, Pb²⁺, Zn²⁺ and Cr⁶⁺. The effects of contact time, initial ion concentration, PH and temperature of the ion solution were discussed. And the selective adsorption of multicomponent ions solution was investigated by the products.The magnetic chitosan beads had sufficient magnetism to separate and collect themselves from water solution. By SEM and BET, the magnetic chitosan beads were spherical, and there was plenty of mesoporous on the surface. The structure of the product was characterized by FT-IR. The C₂-NH₂ and C₆-OH were the functional groups in the magnetic chitosan for the adsorption of heavy metal ions. The 430 mg/L Cu²⁺ and Pb²⁺ mixed solution was selectively separated by using the magnetic chtitosan beads. The adsorption capacity of the magnetic chitosan for the metal ions kept 80.6% after 7 times reuse.Compared with the magnetic chitosan, the magnetic amination chitosan had more C₂-OH positions, the better column filling and chemical adsorption capacity for heavy metal ions. After 7 times reuse, the adsorption capacity for metal ions kept 85.3%. In the way of regulating pH, the magnetic amination chitosan beads were used to selectively separate the 200mg/L Cu²⁺, Zn²⁺ and Cr⁶⁺ mixed solution.The products were used to analyze and describe the adsorption behavior and process of metal ions. In the adsorption experiment, the adsorption was performed at the concentration range of 30mg/L and 1600mg/L, and three temperatures. The equilibrium was reached at 6 h. Four thermodynamics and three kinetics models were used to analyze the adsorption date and describe the adsorption process.The Freundlich and Generalized models yielded the best fit than other models. The adsorption occurred in heterogeneous surfaces with a uniform energy distribution, and it is reversible. With the increase of adsorption time and initial concentration, more heavy metal ions were adsorbed by multilayer absorption and chemical adsorption.The Dubinin-Radushkevich model was chosen to estimate the characteristic porosity and the apparent free energy of adsorption. When the concentration reached a threshold value, adsorption by layering on the surface turned into volume filling. In this experiment, the volume filling rate was approximate 14.37%.The pseudo second-order equation indicated that the rate limiting step was chemical adsorption. At the beginning, the adsorption process was a physical adsorption, which occurred very rapidly, but very unstable. After that, the chemical adsorption capacity raised steadily through the sharing or exchange of electrons, coordination and chelation, until the adsorption capacity reached equilibrium.