Modification And Application Of Protonated Cross-linked Chitosan Adsorbent

With the development of industry, in many fields such as metallurgy industry willproduce amounts of sulfate wastewater. It will causing serious pollution to theenvironment and threaten human health. Chitosan is a natural macromolecular material.Chitosan and its derivative have many useful features, for example, hydrophilicity,biocompatibility, non-toxic, biodegradability, etc. Chitosan molecules containing a lotof activity of amino and hydroxyl groups that can be modify easily. So chitosan and itsderivative are good adsorbent. But they are not stable in acid medium. And adsorptionperformance of anions is very weak.A novel absorbent was prepared by inverse suspension method with chitosan as theraw material, formaldehyde as the amino-group protective agent and glutaraldehyde ascrosslinking agent. In the process of preparation of experiment, the effects of thecrosslinking reaction time, the crosslinking reaction temperature, the amount offormaldehyde and glutaraldehyde on the adsorption amount are studied in detail. Thepreparation conditions of the adsorbent were optimized by orthogonal experiments wereinvestigated. The materials are characterized by analysis means of the SEM?FTIR andEDS. The results show that the optimization crosslinking conditions are determined asfollows: the temperature of crosslinking reaction is50?,the time is6h, the volume offormaldehyde is15mL and the volume of glutaraldehyde is1mL. The SEM?FTIR andEDS show that the preparation and adsorption have been occurred. The stability of thecross-linked chitosan has great improvement than chitosan in acid medium. And thatprovides the possibility for protonate modification. Then the cross-linked chitosan was protonated to make a novel adsorbent forsulfate in the water. In adsorption experiments, discussed of the adsorption time, thetemperature, pH and the initial concentration of sulfate on influence of adsorptionproperties of the adsorbent. The isotherm and kinetics of the adsorption wereinvestigated. Then the regeneration of the adsorbent was carried out. The results showthat the modified the protonation of the cross-linked chitosan adsorbent has a goodadsorption capacity for the sulfate in the water. And when1h for the equilibrium time,25?for the temperature,600mg/L for the concentration of sodium sulfate solution and3.8for the pH, adsorption performance of the adsorbent to achieve the best. It showsthat the equilibrium sorption process follows Langmuir isotherms well and belongs tothe single layer adsorption. In addition, the adsorption process of sulfate ions could beexplained by the second-order kinetic model. The regeneration performance of theadsorbent is excellent and can be used repeatedly.In order to improve the adsorption performance of materials further, after thecross-linked chitosan is activated, it was made for amination modification. Theamination cross-linked chitosan was prepared. Then the cross-linked chitosan wasprotonated to make a novel adsorbent for sulfate in the water. The optimization reactionconditions of the activation and amination modification are studied. The materials arecharacterized by analysis means of the SEM?FTIR and EDS. Finally, the several kindsof adsorbent were compared. The results show that the optimization of the activationreaction condition are determined as follows: the reaction time is6h, the reactiontemperature is50?, the amount of ECH is1.8mL, the concentration of a solution ofsodium hydroxide is0.4mol/L; the optimization of amination modification conditionsare determined as follows: the reaction time is21h, the reaction temperature is60?,the amount of amination agent is4mL. The SEM?FTIR?EDS and XRD show that thepreparation and adsorption have been occurred. The comparative experiment resultsshow that: the cross-linked chitosan adsorbent of protonated amination modification isbetter than other kinds of adsorbent.