Preparation Of Chitosan Based Composite Materials And Their Application In Adsorption Of Cobalt Ion

Because of the chemical toxicity and radioactive hazard of Co²⁺ ,wastewater containing cobalt is one of the environmental problems that need to be paid attention to and solved.Adsorption is a simple and efficient method to remove cobalt ions.Chitosan?CS?is the second largest natural polymer with low price and biodegradability.It has good adsorption performance for many metal ions.It is a potential biosorption material.However,chitosan itself has some defects,which limit its application in practice.Therefore,in order to improve the adsorption capacity,chemical stability and separation performance of the adsorbent,a series of chitosan based composite materials were designed and prepared,and the adsorption characteristics of the prepared materials for Co²⁺ were investigated.Then the adsorption mechanism was analyzed by various characterization methods.The specific research contents are as follows:Firstly,chitosan modified by EDTA?CS-EDTA?was designed and prepared by chemical grafting method.The process of adsorption and removal of Co²⁺ in aqueous solution was studied.The influence of adsorption time and initial ion concentration on the adsorption process was investigated.It is found that the adsorption process of CS-EDTA for Co²⁺ follows the pseudo-second-order kinetic model and Langmuir isotherm adsorption model,and the adsorption between adsorbent and adsorbate is chemical adsorption and monolayer adsorption.Secondly,CS-EDTA material is not easy to separate and recover,so it is compounded with magnetic material to improve the reusability of adsorbent.The EDTA modified magnetic chitosan material?Fe₃O₄@CS-EDTA?was designed and prepared.The shape of the material was spherical particles with uniform size,stable chemical properties and strong magnetic property,which was easy to recover.The saturated adsorption capacity of(Fe₃O₄@CS-EDTA to Co²⁺ is 48.78 mgg·-1.The adsorption process of Co²⁺ follows pseudo-second-order kinetic model and Langmuir isotherm adsorption model,and the adsorption reaction is endothermic spontaneous process.In the cycle experiment,the removal rate of Fe₃O₄@CS-EDTA can still reach 84.5% after 5 cycles of adsorption.The adsorption mechanism of Co²⁺ by Fe₃O₄@CS-EDTA was discussed.The results showed that the main sources of Co²⁺ adsorption by Fe₃O₄@CS-EDTA were the amino and carboxylate from EDTA.Finally,chitosan composite?CS-n ZVI?loaded with zero valent iron nanoparticles was prepared by physicochemical adsorption.Nano zero valent iron dispersed well on the prepared chitosan spheres,and there was no obvious agglomeration.The saturated adsorption capacity of CS-n ZVI for Co²⁺ is about five times that of unmodified chitosan.The adsorptionprocess of CS-n ZVI for Co²⁺ follows a pseudo-second-order kinetic model,indicating that chemical adsorption is the rate control step.The adsorption performance of CS-n ZVI can be kept stable for a long time in the dry and oxygen-free environment.According to the XRD and XPS spectra of CS-n ZVI before and after the adsorption of Co²⁺ ,the oxidation-reduction reaction of n ZVI and Co²⁺ occurred in the adsorbent.The iron ions produced in the reduction process of nano zero valent iron can be complexed by chitosan to avoid the secondary pollution of iron ions.