Preparation And Application Study Of Cationic Starch/Chitosan Crosslinking Copolymer Flocculant (CATCS)

A crosslinking-copolymer flocculant named CATCS was prepared with corn starch and chitosan as raw material in this paper for the first time. The synthesis condition of flocculant CATCS was determined by single factor experiments and orthogonal optimization experiments. The structure and surface morphology of CATCS was characterized using Fourier infrared and scanning electron microscopy technique. The surface charge property of CATCS was characterized by electrophoresis. Thermogravimetry and differential scanning thermal analysis were carried out to investigate its thermal properties. In this thesis, flocculating experiments in kaolin suspension and actual wastewater were carried out with CATCS. Moreover, decolorization of dye solutions and printing and dyeing wastewater and the flocculation removal of hexavalent chromium by flocculant CATCS were investigated. Research results are summarized as following:(Ⅰ) The optimal synthetic condition was confirmed:crosslinking temperature was 70℃;ω(Cat St):ω(CS) was 5:1 g/g; the ration of crosslinker and cationic starch was 0.75 mL/g and reaction time was 1.5h. CATCS was positive charged; the surface of CATCS was rough; the pyrolysis temperature of CATCS was low and range and its glass transition temperature, crystallization temperature and melting temperature was lower than that of raw materials.(Ⅱ) Kaolin suspension and actual wastewater were processed by CATCS. The effects of temperature, pH, amount of CATCS, stirring speed and other factors on flocculation efficiency were tested and comparative experiments were carried out. Flocculation performance CATCS of in 0.5%kaolin suspension was better than that of cationic starch and chitosan, chitosan easily showed deflocculation phenomenon, but CATCS didn't. To achieve the same removal rate (70%～80%) of COD for the wasterwater, the dosage of CATCS was only tenth of that of ferric sulfate. Water content of floc by CATCS, PAM and ferric sulfate was 85.65%,87.26%and 90.95, respectively. The moisture of the sludge treated by CATCS was lower than those by ferric sulfate and polyacrylamide. The dewatering performance of CATCS was better than those of ferric sulfate, aluminum chloride and Ply-ferric sulfate; the dewatering rate of the sludge by aluminum chloride, ferric sulfate, poly-ferric sulfate, PAM and CATCS was 3.48mL/min, 2.95 mL/min,6.54 mL/min,9.24mL/min and 8.43mL/min, respectively. The dehydration rate of the sludge by CATCS was faster than PAM in previous 18min, but mean dehydration rate was lower than PAM. (Ⅲ) Decolorization of four dye solutions, a real dye wastewater and mixed dye wastewater by CATCS were investigated. The effects of initial pH, dosage of CATCS, initial dye concentration, concentration of NaCl electrolyte and absorption time on decolorization ability of CATCS were studied.Thermodynamic studies showed that the flocculation isotherms of decolorization of various dyes by CATCS may be described several isothermal models commonly. Temperature played an important role in the process of decolorization and had great impact on the thermodynamic behavior. The value ofΔH in decolorization process of each dye solution was over 40 kJ/mol, which indicated the existence of chemical reaction in the process. As the temperature increased, the values ofΔG become more negative. In addition, theΔS were positive, indicating the flocculating process was a process of increasing entropy. The increase of temperature was benefit for the flocculation of various dye solutions by CATCS.Decolorization kinetics studies have shown that:the kinetics of decolorization of various dyes by CATCS are highly relevant to the pseudo second order kinetics equations., the equilibrium adsorption capacity calculated by the pseudo second order kinetics were very closed to the experimental values. Flocculating process of various dyes solutions by CATCS may be described excellently. Change of adsorption rate constant with changing temperature was inconsistent for different dye solutions. The flocculation mechanism of adsorption at different temperatures may also be different, which resulted in adsorption rate constant varied with the change of temperature. The activation energy in the reaction was calculated to be 27.74kJ/mol,51.71kJ/mol,-1.93kJ/mol and-14.31kJ/mol, respectively.The decolorization for real dye wastewater and simulated wasterwater:the decolorization efficiency was over 93%by CATCS of 0.15g/L-0.42g/L. To get a decolorization of 90%for real dye wasrewater, the dosage of activated carbon was deminded to be over 2g/L; The absorbance of simulated wastewater in the wavelength of 400-800 nm were 0-0.08 treated by 0.89g/L CATCS, the removal of the dye was more than 98%. Those treated by 14.83g/L activated carbon was 0.1-0.19. CATCS appeared to be much more efficient than those of activated carbon in decolorliaztion for the real dye wastewater and simulating dye wastewater.(V) The removal behavior of CATCS for hexavalent chromium was studied. The influence of CATCS dosage, nitial concentration of Cr(VI), initial solution pH, reaction time and temperature on the removal effect of Cr(VI)by CATCS were discussed. Thermodynamic studies showed that the adsorption isotherms of Cr(VI) on CATCS was described by Freundlich isotherms model well. The chang of Gibbs free energy (ΔG) was 16.75 kJ/mol.The flocculation reaction process of remove Cr(VI) was endothermic.AG at all temperature studied were negative. As the temperature increased, AG becomes more negative suggesting the reaction trended to occur at a higher temperature. In addition, entropy changeΔS was positive to note elevating temperature was conducive to the for removal of Cr(VI) by CATCS.The kinetics of removal of Cr(VI) by CATCS can be elaborated by pseudo second order kinetics mechanism. The equilibrium adsorption capacity calculated by pseudo second order kinetics was much closed to the experimental value. The correlation coefficient squared values of this model were over 0.999, which were much higher than those of pseudo first order. The activation energy in the reaction was calculated to be 29.16 kJ/mol.