Study On Preparation, Characterization And Flocculating Performance Of PAC-PDMDAAC Hybrid Flocculant

Coagulation process has already become one of the most important part in watertreatment. The core technology of coagulation process is the development of flocculants,which determined not only the flocculation effect but also the entire water treatmenteffect. Currently, because of the continuous decrease of water resources and theincreasing discharge scale of wastewater, the composition of contaminants in water ismore complex and the harm to the environment is increasing. Development of newefficient quality flocculants to improve flocculation effect in water treatment, reducecosts and expand new application fields, has already become the focus of research inwater treatment field.Polyaluminum chloride-poly diallyl dimethyl ammonium chloride (PAC-PDMDAAC) hybrid flocculant is a new efficient flocculant which is developed basedon the strong electric neutralization capacity of PAC and the excellent adsorptionbridging capacity of PDMDAAC. Compared with traditional inorganic flocculant, it hascharacteristics of fast floc formation, high particle density and fast settling velocity. Inaddition, this new hybrid flocculant has no secondary pollution, high efficiency withlow cost, and can replace expensive organic polymer flocculant. PAC-PDMDAAChybrid flocculant has excellent prospects for development and application. It will playan important role in drinking water, textile wastewater and dyeing wastewater treatmentprocesses.The main contents and conclusions in this study are as follows:(1) The ionic bond PAC-PDMDAAC hybrid flocculant was prepared by usingpolyaluminum chloride and diallyl dimethyl ammonium chloride as raw materials,ammonium persulfate as the initiator in situ hybridization method. The Box-Behnkenmathematical relational model was established and response surface analysis wasintroduced. The optimum preparation conditions were: DMDAAC mass fraction37%,initiator mass fraction0.6%, reaction temperature75℃and reaction time5h. FT-IRand TGA test results showed that the organic and inorganic components were connectedby ionic bond between the chain end of PDMDAAC (-SO42-) and hydroxy aluminumparticles which had positive charges. SEM results showed the particle size and specificsurface area of PAC-PDMDAAC hybrid flocculant were larger than PAC-PDMDAACcomposite flocculant. (2) The covalent bond PAC-PDMDAAC hybrid flocculant was prepared by usingKH570as modifying agent, polyaluminum chloride and diallyl dimethyl ammoniumchloride as raw materials, ammonium persulfate as the initiator in sol-gel method. Theresponse surface analysis was introduced. The optimum preparation conditions were:DMDAAC mass fraction33%, initiator mass fraction0.6%, reaction temperature64℃and reaction time3h. In the flocculant structural characterization analyzes,conductivity, FT-IR,13C-NMR and TGA results showed there was covalent bondbetween organic and inorganic components in PAC-PDMDAAC hybrid products. ItsSEM photograph showed the hybrid flocculant had loose structure and large particlesize.(3) Through coagulation experiment of kaolin simulated water and sedimentationexperiment of diatomite simulated water, the charge neutralization and flocculatingperformance of PAC and two kinds of hybrid flocculants were investigated. The kaolincoagulation experiment showed that the charge neutralization capacity of ionic bondPAC-PDMDAAC hybrid flocculant was the strongest. While charge neutralizationcapacity of covalent bond hybrid flocculant was also more prominent. In thesedimentation experiment of diatomite simulated water, these two kinds of hybridflocculant had larger floc size and higher sedimentation rate than PAC, which playedexcellent flocculating performance. In coagulation tests of Chongqing Jialing River andthe Yangtze River, the two hybrid flocculants showed excellent removal efficiencies onturbidity, UV254and CODMn.(4) Coagulation dynamic process of kaolin simulated water was studied by usinglaser particle size analyzer. The floc size was larger with the increase of dosage and thepH close to neutral when these two hybrid flocculants were used. Compared with PAC,the stable floc formation time was shorter in hybrid flocculants. In the same shear forces,these two kinds of hybrid flocculants had stronger shear resistances and recoverycapabilities than PAC. As the extension of broken time, the strength factors andrecovery factors of the two kinds of hybrid flocculants decreased.(5) The flocs of hybrid flocculants after flocculation were observed by scanningelectron microscope. Flocs could be divided into three different stages. By assumingthat the particle-bond location met regular tetrahedron, floc structure model wasestablished， which to some extent reflected the floc structure of kaolin particles byhybrid flocculants.