Adsorption Of Cr(VI) Using Metal-crosslinked Chitosan Complex

Cr(VI) has been internationally recognized as one of the carcinogenic metal, which is toxic and can enrich through food chain in living organisms. Research on removal of Cr(VI) must be done without delay. Chitosan(CS) is considered as an ideal adsorbent and valued by more and more researchers in water treatment because of its abundantly availability, low cost, less secondary pollution, etc.A metal-chitosan complex (Fe-CS) and cross-linking chitosan (ACOH-CS) were prepared. Both Fe-CS and ACOH-CS were used as adsorbent for the removal of Cr(VI) from aqueous solution. Fe-CS, Fe-CS after adsorption of Cr(VI) and Fe-CS after desorption were characterized by using X-ray photoelectron spectroscopy (XPS). The results were as follows.(1) The kinetic experimental data correlated well with the second-order kinetic model, indicating that the Fe-CS adsorption for Cr(VI) was the second rate-limiting step. When the initial concentration of Cr(VI) ranged from 50 to 200 mg/L,adsorption rate of Fe-CS was several times higher than ACOH-CS. The order of adsorption rate constant k2 was k2-50>k2-ioo> k2-2oo-The max adsorption rate of Fe-CS k2.50-6.66 min-1.g/mg.(2) Adsorption capacities of Fe-CS for Cr(VI) whose initial concentration ranged from 0 to 200 mg/L, were measured at 30℃, which indicated that adsorption capacities of Fe-CS increased together with the increase of initial Cr(VI)concentration. The max adsorption capacity at 30℃was 145mg/g.(3) Fe-CS possessed acid resistance, which showed good adsorption property in the situation of low pH.The adsorption capacity of Fe-CS for 200mg/L Cr(VI) was 94.68 mg/g when pH=4, which was 1.65 times that of ACOH-CS in the same pH.(4)Coexisting cations (Na+,Mn2+,Ca2+,Mg2+,Cu2+) did not have an effect of inhibition on Fe-CS'adsorption propert.(5) XPS spectroscopy indicated that-NH2 complexed with Fe(III), and Fe atom of Fe-CS appeared in the state of Fe(III); the Cr(VI) bound to Fe-CS was reduced to Cr(Ⅲ); carbon atom of CS was not complexed with Fe(III) in the process of Fe-CS formation and adsorption. It was speculated that Fe(III) and-NH3+of Fe-CS interacted with Cr2O72- of aqueous solution by electrostatic effect, which might be the dominated mechanism of Fe-CS'efficient adsorption property.Therefore, the results showed that the metal-chitosan complex Fe-CS was favourable adsorbent for the removal of Cr(VI) from aqueous solution.