Strength of aluminium hydroxide flocs

François, R.J.

doi:10.1016/0043-1354(87)90023-6

Cited by 172 publications

(101 citation statements)

References 16 publications

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“…However floc strength is harder to characterize and there is, as yet, no straightforward technique to characterize the floc strength experimentally. Generally, there are two modes of floc rupture [18], surface erosion and large-scale fragmentation [19,20]. Researchers [20][21][22] found a correlation between floc size and the strength for a given rate of shear condition.…”

Section: Floc Strengthmentioning

confidence: 99%

“…Generally, there are two modes of floc rupture [18], surface erosion and large-scale fragmentation [19,20]. Researchers [20][21][22] found a correlation between floc size and the strength for a given rate of shear condition. Spicer and Pratsinis [23] studied on the flocculation of polystyrene particles in a stirred tank and pointed out that the average floc structure became less open or irregular as the floc size distribution attained steady state as a result of shear-induced breakage or restructuring.…”

Section: Floc Strengthmentioning

confidence: 99%

“…Bache and Rasool [24] gave the value of slope, which varied between 0.44 and 0.64, for alumino-humic flocs under low alkalinity conditions. Francois [20] concluded that the values of γ were around 0.5 for all types of floc formed by alumino-kaolin under different aluminum sulphate dosage. Spicer et al [25] investigated the effect of shear history on the evolution of polystyrene-alum floc size, density and structure by small angle light scattering, the floc structure was characterized by the mass fractal dimension, D F , and the relative floc density.…”

Section: Floc Strengthmentioning

confidence: 99%

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Characterization of floc size, strength and structure under various coagulation mechanisms

et al. 2006

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Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107) N sweep (0.5618) N bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m − 2 . An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated.

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Section: Floc Strengthmentioning

confidence: 99%

Section: Floc Strengthmentioning

confidence: 99%

Section: Floc Strengthmentioning

confidence: 99%

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Characterization of floc size, strength and structure under various coagulation mechanisms

et al. 2006

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“…In the previous research, characteristics of flocs formed in the coagulation process by metal salts have been well understood (Jarvis et al, 2005a;Francois, 1987;Spicer and Pratsinis, 1996;Chakraborti et al, 2000). The accurate estimation of flocs characteristics is valuable for evaluating water treatment performance under certain coagulation conditions.…”

Section: Introductionmentioning

confidence: 99%

Characterization of kaolin flocs formed by polyacrylamide as flocculation aids

Zhu

et al. 2009

International Journal of Mineral Processing

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a b s t r a c t a r t i c l e i n f oAlthough the synthetic organic polymers have been widely applied as flocculant aids to improve solid-liquid separation efficiency, it is not very clear how the charge type and molecular weight of the polymers influence the characteristics of flocs. In this paper, floc characteristics, such as floc size, density, structure, strength and reversibility were investigated in details in terms of their response to the polyacrylamide (PAM) with different charge types and molecular weights. Laser light scattering, image analysis and settling technology were employed simultaneously. The results showed that floc size induced by anionic PAM with medium molecular weight (A130) and ultra high molecular weight (A115) was 419 µm and 438 µm respectively, correspondingly, floc size induced by cationic PAM with medium molecular weight (C448) and very high molecular weight (C498) was 731 µm and 796 µm. Meanwhile, floc fractal dimension was inversely proportional to polymer molecular weight and the values were between 1.91 and 2.40. In addition, floc density was affected by molecular weight of anionic PAM more dramatically than that of cationic PAM. For a given floc size, the density increased with molecular weight. Furthermore, flocs formed by cationic PAM showed much greater shear-resistant ability and reversibility than anionic PAM. Nevertheless, the poor reversibility of the flocs formed by high molecular weight was also observed. An explanation for the resultant floc characteristics was offered in terms of flocculation mechanisms.

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“…After breakage, slow mixing at 40 rpm was reintroduced for anther 15 min to allow the floc re-formation. The relative breakage and re-growth of different flocculated systems have previously been expressed by use of floc strength and recovery factors [19,20] which may be calculated as follows:…”

Section: Floc Strength Recovery Ability and Structure Analysesmentioning

confidence: 99%