Preparation And Performance Of Cationic Starch Graft Polyacrylamide And Fe₃O₄@Graft Copolymer

Advanced treatment of coking waste water with low cost and high efficiency is a worldwideproblem. Flocculants based on natural polymers like starch and chitosan have been acclaimed asgreen flocculants of21th century, which are expected to open a green way for advancedtreatment of coking waste water. In the structure of starch grafting polyacrylamide and dimethyldiallyl ammonium chloride, St-g-P（AM-DMDAAC）, flexible PAM and positively chargedPDMDAAC branched chains are attached to hydrophilic and semirigid chains of starch.Consequently the grafted copolymers possess both the characteristics of natural polymers andsynthetic polymers, such as mechanical and biological stability, linear extensibility and chargeneutrality. Magnetic microspheres are composite materials of polymers and inorganic magneticparticles. The magnetic composite materials show the uniqe application prospect for thecombination of mangnetic responsiveness and special structure property of microspheres.In this study, cationic starch graft PAM was prepared in two steps with microwave synthesistechnology in salt solution. The copolymers were used to coat Nano Fe₃O₄to form Magneticmicrospheres. The two kinds of products were applied to advanced treatment of coking wastewater. The detailed study is as follows.After the removal of protein and lipid by optimized pretreatment process, the gelatinizationdegree of starch was significantly improved. The gelatinization transmittance exceeded60%which was superior to native starch and other pretreated starch.Single factor experiments about pretreated starch grafting PDMDAAC were carried out. Tothe indexes of grafting efficiency, percent grafting and cationic degree, the optimal conditions forgrafting PDMDAAC were: concentration of pretreated starch1.5g/70mL, concentration ofZnCl22g/70mL, pH of reaction system9, concentration of potassium persulfate2mmol/L,mass ratio of DMDAAC to pretreated starch4:1, microwave irradiation time150s, microwaveirradiation power600W.Single factor experiments and orthogonal experiments about cationic starch grafting PAMwere carried out. To the indexes of grafting efficiency, percent grafting and cationic degree, theoptimal conditions for grafting PAM were: concentration of pretreated starch1.5g/90mL, pH ofreaction system9, concentration of supplementary ZnCl21.5g/90mL, concentration ofsupplementary potassium persulfate1mmol/L, mass ratio of AM to pretreated starch3.3:1,microwave irradiation time180s, microwave irradiation power700W. Under the optimalconditions, indexes of St-g-P（AM-DMDAAC） were: grafting efficiency88.57%, percent grafting167.08%, cationic degree0.7897mmol/g, average molecular weight4.62×106Da.FTIR spectroscopy, SEM analysis and X-ray diffraction were employed to confirm that DMDAAC and AM had been grafted onto pretreated starch backbone. The structure of thecopolymers gradually demonstrated some potential applications.Nano Fe₃O₄were coated by St-g-P（AM-DMDAAC） with self-assembly embedding method.FTIR spectroscopy, SEM analysis and X-ray diffraction were employed to confirm that magneticpolymer microspheres had been prepared successfully. After calculation, particle size wereobtained: Fe₃O₄9nm, St-g-P（AM-DMDAAC）-Fe₃O₄21nm.Inorganic flocculants and St-g-P（AM-DMDAAC）, together with St-g-P（AM-DMDAAC）-Fe₃O₄and surfactant CTAB, were applied to advanced treatment of coking waste water. Aftersingle factor experiments and orthogonal experiments, to the indexes of removal rates of chroma,CODCrand turbidity, the optimal conditions for waste water treatment were: without adjustingpH, PFS dosage1.2g/L, St-g-P（AM-DMDAAC） dosage3mg/L,[St-g-P（AM-DMDAAC）]-Fe₃O₄dosage15mg/L, CTAB dosage62.5mg/L. Under the optimal conditions, in dealing withraw coking waste water （chroma320°and CODCr160.52mg/L）, chroma and CODCrremovalrate can reach89.06%and57.69%（chroma35°and CODCr67.91mg/L）. Synthetic graftedflocculant is superior to commercial CPAM for CODCrand chroma removal in cokingwastewater treatment.