The effect of second coagulant dose on the regrowth of flocs formed by charge neutralization and sweep coagulation using titanium tetrachloride (TiCl <inf>4</inf>)
- Publication Type:
- Journal Article
- Journal of Hazardous Materials, 2011, 198 pp. 70 - 77
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Characteristics of flocs formed by charge neutralization and sweep coagulation using titanium tetrachloride (TiCl 4) were investigated with humic acid-kaolin suspension by continuous optical monitoring. This paper focused on the regrowth ability of broken flocs after addition of second TiCl 4 dose. Variation of floc size and the fractal dimension of flocs versus second TiCl 4 dose after regrowth were investigated. Second TiCl 4 dose was added during the floc breakage period, and addition time of second TiCl 4 dose was also investigated. The results showed that, when coagulated by charge neutralization at pH 6, an appropriate second TiCl 4 dose improved regrowth ability of broken flocs at low initial TiCl 4 doses. While for high initial TiCl 4 doses, second TiCl 4 dose lowered floc re-growth ability. When coagulated by sweep coagulation at pH 10, second TiCl 4 dose made regrown flocs larger than those without second TiCl 4 dose. Floc structure analysis showed that it was determined by not only the fractal dimension of flocs, but also the chemical characteristics of floc surface. Addition time of second TiCl 4 dose had a great effect on floc regrowth ability, suggesting that the broken flocs had better regrowth when second TiCl 4 dose was added at the end of the breakage period. © 2011 Elsevier B.V.
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