| Coagulation process has already become one of the most important part in water treatment. The core technology of coagulation process is the development of coagulant, which determined not only the coagulation effect in water treatment but also the cost of whole coagulation process. Recent years, with the dramatic increasing amount and the complex composition of contaminants of waste water, the affordable and effective coagulant products are in great need by the whole industry, which impels and justifies the research and invention of innovative coagulants.Cationic polymer coagulant-poly diallyl dimethyl ammonium chloride (PDM) with the advantages of high charge density, morphology stablility, non-toxicity, has attracted wide attention. With PFC-PDM prepared by the co-polymerization and composite polymerization, this study focuses on the difference of coagulation characteristics, structural characteristics, and floc characteristic in the treatment of drilling wastewater between PFC and PFC-PDM.Considering the different influence of the composite ratio (P=PDM/PFC), PDM molecular weight, of the composite prepared by PFC-PDMm, and copolymers prepared by PFC-PDMc on the Fe (III) form distribution and Zeta potential, the better prepration method is determined. The results showed that there is a huge gap between PFC-PDMm with PFC-PDMc on the composite ratio and the molecular weight:①With the increasing composite ratio, the amount of effective iron as Feb in PFC-PDMm increased, and Fec content increased significantly in PFC-PDMc.②The Zeta potential of PFC-PDMm and PFC-PDMc is much higher than that of PFC, and increases with higher composite tatio. So, PFC-PDMm floc with higher surface charge is more capable of electric neutralization.③The molecular weight of PDM has similar effect on both PFC-PDMm and PFC-PDMc:In both PFC-PDMm and PFC-PDMc, the amount of Feb decreases while the amount of Fec increases, along with increasing molecular weight of PDM④Under the same composite ratio condition, the Zeta potential of PFC-PDMm and PFC-PDMc increases with the increasing of PDM molecular weight and it was caused by the high charge density of heavy PDM. Studies have shown that appropriate composite ratio and molecular weight of PDM can greatly promote coagulants efficiency. The results showed that P=0.3and PDM molecular weight as200000-350000is the best condition for PFC-PDMm production.With the analysis of IR, TG and SEM for PFC and PFC-PDMm, studies showed that:①The IR spectra of PFC-PDMm was similar with PFC, but some peaks are distorted. Further analysis showed that PFC-PDMm has higher degree of hydroxyl association than PFC, and there were differences in content of hydroxyl bridge and oxygen bridge in Fe between PFC-PDMm and PFC.②Compared with that of PFC, weight loss peak of PFC-PDMm is around300℃～400℃which thanks to methyl-out in quaternary ammonium groups on PDM and polymer chains of PDM fixed by hydroxy iron particles.③At low magnification scanning, PFC-PDMm presented more regular porous honeycomb. At high magnification scanning, there was spherical and ellipsoidal irregular protrusions in the face of PFC-PDMm which was in favor of the role of adsorption and sweep netting.Analysis of the particle size, structural shape, density and their interactions can explain the differences in the characteristic of PFC and PFC-PDMm floc in treatment of drilling wastewater. The floc characteristics of PFC and PFC-PDMm treated drilling wastewater in three different coagulation mechanisms showed:①PFC and PFC-PDMm floc size increased with weaker stir intensity. According to slope y of ln(d)-ln(G),the PFC-treated wastewater floc strength was in the order of bridging> sweep>electrical neutralization, while PFC-PDMm-treated wastewater floc in the order of bridging> charge neutralization> sweep, which is consistent with theroritical calculation.②Under three coagulation mechanisms the floc of PFC-treated wastewater and PFC-PDMm-treated wastewater, fractal dimension of flocs increased with higher stir intensity. Other things being equal, the floc fractal dimension of PFC-treated wastewater was in the order of sweep>charge neutralization>bridging, while that of PFC-PDMm-treated wastewaterin the order of bridging> sweep> electric neutralizing.③An intrinsic unity of relationship between fractal dimension and floc strength under the three coagulation mechanisms demonstrated. The fractal dimension and floc strength is solely determined by the type of coagulant.④In the drilling water treatment experienments, with the dosage as6000mg/L, the PFC-PDMm showed better performance as19.16%higher COD removal rate and13.82%lower Setting Vslocity (SV), than PFC.The difference in the intermolecular bonds, the morphology, floc characteristics between PFC and PFC-PDMm showed that PFC-PDMm. is not a simple mixture of PFC and PDM.The effective interactions between inorganic and organic component within PFC-PDMm can greatly promote the coagulation. |
