Adsorption Behaviors And Mechanisms Of Gold (Ⅲ), Silver (Ⅰ) And Other Heavy Metals Onto Novel Chelating Resins Derived From Chitosan

With the pollution caused by industrialization and urbanization becoming more and more severe, heavy metal pollution has been a global problem. Therefore, dealing with heavy metal pollution in water has become an important facet of protecting environment to each country. Furthermore, recovery of precious metals will not only solve the environmental problems but also have profitable potential,which has been a critical aspect of protecting environment.Chitosan has been widely used in many fields for its good environmental compatibility, renewability, abundant resources and low cost. Hence, an efficient way to get chelating resin is to modify chitosan's structure, and the resins produced have been testified that they can selectively adsorb many kinds of heavy metals in aqueous medium, which has drawn more and more attention.In this study, epichlorohydrin cross-linked chitosan resin, epichlorohydrin cross-linked carboxymethylated-chitosan resin, glutaraldehyde cross-linked carboxymethylated-chitosan resin, thiourea modified carboxymethylated-chitosan resin and magnetic chitosan resin were designed and synthesized. FTIR,SEM were used to identify the structures and characteristics of the resins and adsorption experiments were used to testify the adsorption capacity of the synthesized resins for various heavy metals such as Au³⁺, Ag⁺, Hg²⁺ and Pb²⁺. Exprimental data showed that thiourea modified carboxymethylated-chitosan resin has better adsorption capacity and selectivity for most of the studied heavy metals and the maximum adsorption capacity for Au³⁺,Ag⁺,Hg²⁺and Pb²⁺ was found to be 8.32, 3.77, 6.29 and 1.20 mmol/g. The adsorption behavior for Au³⁺,Ag⁺,Hg²⁺ and Pb²⁺ onto the thiourea modified carboxymethylated-chitosan resin was systematically studied respectively using batch method. We also performed metal ions co-adsorption experiment to study the resin's selectivity. In addition, we synthesized the template resin of thiourea modified carboxymethylated-chitosan to study its adsorption capacity and mechanisms. The effects on adsorption capacities of the resin such as contact time, temperature, pH value of the initial solution, and initial concentration of solution were all investigated through batch method.The kinetic parameters of the adsorption process were obtained, and the results indicated that adsorption process for Au³⁺, Ag⁺, Hg²⁺ and Pb²⁺ kinetically followed pseudo second order model. The thermodynamic data showed that Langmuir equation could describe the adsorption process for Au³⁺, Ag⁺, Hg²⁺ and Pb²⁺ precisely. The adsorption capacity decreased when the temperature elevated, and the adsorption process was spontaneous exothermic reaction. In the selective experiments, the thiourea modified carboxymethylated-chitosan resin showed especially high selectivity towards Au³⁺, Ag⁺ and Hg²⁺. The results also showed that the desorption efficiency was above 90% and the adsorption capacity of this modified chitosan resin was not significantly changed up to 5 cycles. Therefore, the resin could be easily regenerated and efficiently reused, which indicated the availbility for separating precious metals from other heavy metals in solution. We also used the 0.1g thiourea modified carboxymethylated-chitosan resin to recover silver (I) from waste fixing bath, and the adsorption capacity was 1.08mmol/g. The novel chitosan chelating resin we synthesized in this thesis showed potential in the field of heavy metal treatment and recovery of precious metals.