Flocculation of kaolin suspensions

H Serita, K Murai. Flocculation of kaolin suspension with graft copolymers of ionen. Kobunshi Ronbunshu. 50(7) 564-570, 1993. 

In a series of experiments on the flow of flocculated kaolin suspensions in laboratory and industrial scale pipelines(26-27-2Sl, measurements of pressure drop were made as a function of flowrate. Results were obtained using a laboratory capillary-tube viscometer, and pipelines of 42 mm and 205 mm diameter arranged in a recirculating loop. The rheology of all of the suspensions was described by the power-law model with a power law index less than unity, that is they were all shear-thinning. The behaviour in the laminar region can be described by the equation ... 

Heywood, N. I. and RICHARDSON, J. F. J. Rheology 22 (1978) 599. Rheological behaviour of flocculated and dispersed aqueous kaolin suspensions in pipe flow. 

It is worth noting that the specific resistances obtained by flocculation with cationic polymers are much less than those achieved by simple salts. For instance, when the kaolin suspension is completely destabilized by the addition of a calcium salt, the specific resistance is only reduced by a factor of about two. A ten-fold reduction can easily be achieved by cationic polymers. 

Michaels, A.S. Bolger, J.C. The plastic flow behavior of flocculated kaolin suspension. Ind. Eng. Chem. Fundam. 1962, 1, 153-162. 

The pH of the material surrounding kaolin will determine whether or not its surface will have OH groups. When the pH is above 7, the deprotonation of hydroxyl groups occurs which eliminates the active functional groups from the surface. The chemical changes are consistent with the ability of kaolin to flocculate in suspensions. ... 

As mentioned above, kaolin suspensions are also often used as model dispersed systems for studying flocculation processes to solve important problems in water treatment such as the removal of dispersed impurities. Among the synthetic flocculants, polyacrylamide ones are the most widely used. These flocculants are rather easily available, cheap, and economic. 

The influence of charged acrylamide graft copolymers on the flocculation process of 5% (w/w) kaolin suspensions were investigated by Serita and Murai [17]. The flocculation ability of different copolymers was linked to their structure by measuring the sedimentation potential. An iep of kaolin particles was observed for the concentration of approximately 20 ppm polymer, and they could additionally show that copolymers were more effective for flocculation than typical commercial flocculants. 

Starch-induced flocculation of 1% (w/w) kaolin suspensions and the adsorption of NaCMC were investigated by Jamstrom et al., where the kaolin was partly pretreated with sodium polyacrylate of low molecular weight (PAA) [22], In all flocculation experiments the kaolin suspension as well as the starch solution were adjusted to pH 7.5. The flocculation behavior of the PAA-treated suspension indicated that depletion flocculation is a very likely flocculation mechanism. When a hydrophobically modified starch was added, no flocculation occurred, and no adsorption of the modified starch on the kaolin particles could be detected. It is reasonable that water is a less good solvent for the hydrophobically modified starch and thus may cause the impossibility of depletion flocculation. On the other hand, a dispersing... 

Michaels A.S. and Bolger J.C., 1%2. Settling rates and sediment volumes of flocculated kaolin suspensions, Ind. Eng. Chem. Fundam., 1, 24-33. 

FIGURE 3.10 Flocculation characteristics of various grades of polyacrylamide-grafted agar (Ag-g-PAM) synthesized by (a) conventional, (b) microwave-initiated, and (c) microwave-assisted method, in 0.25% kaolin suspension. 

A.S. Micheals and J.C. Bolger, Settling Rates and Sediment Volumes of Flocculated Kaolin Suspensions, I EC Fimdamentals, 1,24,1962. 

A highly concentrated suspension of flocculated kaolin in water behaves as a pseudo-homogeneous fluid with shear-thinning characteristics which can be represented approximately by the Ostwald-de Waele power law, with an index of 0.15. It is found that, if air is injected into the suspension when in laminar flow, the pressure gradient may be reduced even though the flowrate of suspension is kept constant, Explain how this is possible in slug flow and estimate the possible reduction in pressure gradient for equal volumetric flowrates of suspension and air. 

The flocculated suspension was then transferred to the syringe and the specific resistance was determined as described previously. Results are shown in Figure 4 for three different kaolin concentrations, flocculated with polymer A. The polymer concentration is shown as a percentage of the clay concentration. In all cases, plots of t/D vs. D were linear. 

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