| In this study, the coagulation process of PFS in HA and HA-Kaolin suspension under different mixing ways and initial pHs was investigated. The changes in the zeta potentials of micro-fiocs, turbidity, UV254absorbance, pH, and conductivity of supernatant and the volume of PFS-HA flocs after coagulation-floccualtion-sedimentation with these typical operating factors were analyzed. The results showed that the charge neutralization mechanism played a main role in coagulation of HA and HA-kaolin solution with initial pH=6.00by PFS. The mixing ways had no effect on the determination of he optimum PFS dosage range, while one-stage mixing way in coagulation-flocculation process led to a higher HA removal ratio than two-stage mixing one. When the HA solution was coagulated by PFS at initial pH=8.00, absorption-complexating and flocs sweeping effects became a main coagulation mechanism, and the optimum PFS dose range for coagulation of HA solution at two-stage mixing way was wider than that at single mixing one, then a higher HA removal effect was also observed at the former mixing way.The floc size was monitored by Mastersizer2000, and the result showed that during the PFS coagulation period, the formation of the PFS-HA-Kaolin flocs could be described as following:the dynamic occurrence of the sharp growth-sharp breakage-gradual regrowth process. At the end of coagulation at OCC or RC of PFS, one-stage mixing at intensity of G=84s-1can led to the formation of more compact and larger flocs with much less numbers than two-stage mixing at intensity of G=452/84s-1. Moreover, the floc strength were influenced by pH and mixing way. The flocs formed under one-stage mixing way at OCC dosage of PFS in pH=8.00have stronger floc strength than the flocs which formed at pH=6.00during the first1000s, while after1000s, the floc stength close to each other. When the flocs formed under two-stage mixing way at OCC dosage of PFS at pH=8.00had stronger floc stength than the flocs formed at OCC dosage of PFS at pH=6.00. In addition, PFS hydrolysis results showed that a faster hydrolysis reaction could occure at pH=6.00under one-stage mixing way than pH=8.00. But the PFS hydrolysis rate was slower at pH=6.00under two-stage mixing way than pH=8.00under the same mixing way. In all, two-stage mixing way can lead a faster hydrolysis of PFS than one-stage mixing way.The ESEM images of PFS-HA-kaolin flocs which prepared by freezing-drying method implied that the floc surface topography were somehow different for which formed under different coagulation conditions. The flocs were amorphous structure in the low magnification images. And in the high magnification ESEM images, some breakage-particles can be found in the floc surface. The ultrathin slices-TEM result showed the micro-structure of PFS-HA-kaolin were somehow different for the different coagulation conditions. At OCC dosage of PFS, the structure of of flocs formed at pH=6.00was more compact than pH=8.00. But the quantity of cloud-like formations in the ultrathin-slice at pH=6.00was less than pH=8.00. The ATR-FTIR spectrum of PFS-HA-kaolin flocs and PFS hydrolyzed species showed the PFS-HA-Kaolin flocs formed under aforementioned different coagulation operation conditions exhibited the similar features in their own ATR-FTIR spectra though there were noticeable differences in the relative intensities of individual bands. And the PFS hydrolyzed species showed the similar feature in their ATR-FTIR spectra at the same mixing way. |
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