Growth Kinetics of Hydroxide Flocs

Abstract

This article describes how mathematical expressions of the kinetics of flocculation are applied when a hydrolyzing metal salt is used as the coagulant. It includes not only an evaluation of the phenomena observed but also substantial experimental data.

The role of mixing conditions on floc growth, breakage and re-growth

“…Similar observations have been reported previously for flocs broken after growth at different slow stirring speeds [18] and also in this work (see Section 3.2). The FI values after breakage were always lower than those before breakage, which is typical of flocs formed with hydrolyzing coagulants under 'sweep coagulation' conditions [9,19]. According to previous results [14] when charge neutralization dominates the coagulation mechanism at low pH (where there is little or no hydroxide precipitation), there are only physical bond(s) between destabilized particles and broken flocs can re-grow more or less completely.…”

“…Therefore, increasing the duration of rapid mixing could be important for reducing the number of small flocs. Longer duration of rapid mixing, such as 120 s caused higher residual turbidity compared with that for 60 s. Franç ois [19] considered that a further increase in rapid mixing time gives rise to microflocs breakage and this reduces floc re-growth potential as suggested above. In addition, the residual turbidity mostly became lower after the re-growth of broken flocs, especially for only 10 s of rapid mixing, where the proportion of smaller flocs was lower (Fig.…”

Is electrophoretic mobility determination meaningful for aluminum(III) coagulation of kaolinite suspension?

“…The enmeshment is usually taken as the process in which flocs snare particles. Although there is no consensus about the optimal floc size for enmeshment, it has been found in several typical conditions favoring enmeshment that charge neutralization still occurs, followed by enmeshment [9,31]. In another study, under conditions favoring enmeshment, considerable amounts of polymeric hydrolyzed Al species responsible for charge neutralization were identified after the rapid-mixing stage during Al(III) coagulation [32].…”

Fractal Dimension of Cohesive Sediment Flocs at Steady State under Seven Shear Flow Conditions

“…The Taylor vortices due to flow instability were observed during all the experimental runs because all the angular velocity values of the inner cylinder in this study exceeded this ωi value. To avoid estimating the effects of several mineral compositions on the flocculation process, kaolin (China clay) was used in this experiment because of its obvious flocculation characteristics, as described in many previous experiments [23,[45][46][47][48]. The particle size distribution of the kaolin was determined using a laser particle size analyzer (Horiba LA-920; produced by Horiba Corporation, Tokyo, Japan).…”