Preparation Of Chitosan-glutathione And Its Coagulation Performance Of Chromium (?) Removal

With the rapid development of our country industries such as metallurgy, electroplating,leather processing,paint manufacturing and textile,etc,large chroumuim ions-containing wastewater has been discharged into the aquatic system.The treatment of polluted water by Cr⁶⁺ has become a major challenge to the water environmental researchers.Chitosan?CTS?,a nature high molecular weight cationic polymer.CTS and its modifier often be used as coagulant for the water treatment due to their low toxic,biodegradability and excellent chelating ability.According to the coordination chemistry theory and soft and hard acid-base theory,the sulfur-containing organic compound has excellent complexing ability with heavy metal ions.Therefore,sulfur containing coagulant theoretically has better removal effect on heavy metals.Reduced glutathione?GSH?,is a kind of S-containing organic compounds.It is an ideal reaction monomer for the synthesis of coagulant for treatment of heavy metal due to its molecular chain contaning multiple coordination groups,such as thiol group,amide group,carboxyl group and amino group.In this paper,a high molecular thiolated chitosan coagulant?denoted as CTS-GSH? was synthesized through amidation reaction with reactive monoers including chitosan?CTS? and glutathione?GSH?, N-hydroxy succinimide as protecting agent, 1-ethyl-?3-?dimethylamino? propyl? carbodiimide hydrochloride as cross-linking agent. In this study, the optimum conditions for preparation of CTS-GSH were obtained by examining the effects of parameters, such as reaction monomers mass ratio, reaction time, dosages of cross-linking and protecting reagents as well as the system pH, on performance of CTS-GSH. CTS-GSH was used to treat the modeling wastewater including Cr⁶⁺ in a coagulation-flocculation system. The results showed that Cr⁶⁺ removal efficiency could be up to 90.5% with chitosan/glutathione mass ratio of 1:1, reaction time of 5.0h, 0.25 g cross-linking agent, 0.40 g protecting agent, and pH 3.5, indicating CTS-GSH had a good effect on removal of aqueous Cr⁶⁺.In this paper,the structural characterization of the optimization of CTS-GSH product was studyed,in addition to study on the Near Infrared Determination of thiol content of CTS-GSH. The product structure and performance characterized by IR spectrum and scanning electron microscopy showed that the amidation reaction between monomers was successfully achieved, and the surface of polymer had a good adsorption performance.Differential thermal-thermogravimetric analysis indicates that the product was strong stable and could not be decomposed at room temperature. And ultraviolet spectrophotometric method was used to determine the content of thiol group in the product of CTS-GSH,then near infrared spectra of the product were scanned.The characteristic peaks of each band were used as the independent variables,and the content of thiol group was used as the dependent variable,using partial least squares method to establish the mathematical conversion near infrared reflectance spectroscopy calibration model.With this calibration model to predict the content of thiol group in CTS-GSH,and with comparison of the simulated value and measured value.In this experiment 56 products were used which were self-prepared in the laboratory. The results show that the external validation determination coefficient between simulated and observed values was found to be 0.90,and the distribution trend forecast was good.Statistics showed that there was no significant between simulated value and measured value.And the results show that using the calibration model established by the data of NIRS to predict the content of thiol group in CTS-GSH is of high feasibility.Synthetic wastewater containing Cr⁶⁺ was selected as treatment object, jar test was carried out by using enhanced coagulation. Parameters affecting the coagulation-flocculation process such as the initial concentration of Cr⁶⁺, the dosage of CTS-GSH dosage,slow stirring time,sedimetation time,pH value, turbidity,organic complexing agents,inorganic coordination ions and so on.The results showed that it had better reaction conditions among the initial concentration of Cr⁶⁺,the dosage of CTS-GSH dosage, slow stirring time,sedimetation time and pH value.Controlling the above reaction conditions except for rapid stirring speed,which can be improving the removal rate of Cr⁶⁺;When the waste water containg Cr⁶⁺ containing other substances such as turbidity,organic coordination agents,humic acid,etc.,there were different removal rate of Cr⁶⁺ among these conditions;Turbidity can be promoting it under certain conditions;And other coexistent substances,such as EDAC,sodium salicylate,tartaric acid,citric acid,humic acid, reflected effect of promotion or inhibitation,which was related to the nature and concentration of the substance and differed in various extents of promotion or inhibitation.Controlling the above promoting conditions,which can be improving the removal rate of Cr⁶⁺.And under certain conditions,adding the amount of CTS-GSH dosage can be reducing or eliminating this inhibition;The coexistence metal ions Ca²⁺,Mg²⁺ have an inhibitory effect on Cr⁶⁺ removal rate.The higher of Ca²⁺,Mg²⁺ concentration,the stronger of inhibition.And the inhibitory extents:Mg²⁺>Ca²⁺,adding the amount of CTS-GSH dosage can be reducing or eliminating this inhibition.While the coexistence of inorganic ions SO₄^2-,CO₃^2-have an more significant inhibitory effect on Cr⁶⁺ removal rate.The higher of SO₄^2-,CO₃^2-concentration,the stronger of inhibition.The inhibitory extents:SO₄^2-<CO₃^2-,and adding the amount of CTS-GSH dosage has little function to these.