Kaolin suspension

Farooqi, S. I. and Richardson, J. F. Trans. I. Chem. E. 58 (1980) 116. Rheological behaviour of kaolin suspensions in water and water-glycerol mixtures. 

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 ... 

Table 5.2. Power-law parameters for flocculated kaolin suspensions...

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

Some preliminary experiments have been conducted using the new technique, with kaolin suspensions and cationic polymers. 

Figure 3. Linearized plot for an unflocculated 35 mg/1 kaolin suspension.

Figure 4. Specific resistance of kaolin suspensions treated with different amounts of polymer A. Kaolin concentrations 1) 70 mg/1, 2) 140 mg/1, 3) 280 mg/1.

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. 

Effect of Stirring. The rather small effect of tube flow and slow stirring on the specific resistance results in Figure 5 was unexpected and has been checked by a series of trials in which a kaolin suspension was subjected to various periods of slow stirring, following polymer addition and rapid mixing. 

For this purpose, 500 ml of a 140 mg/1 kaolin suspension was treated with an amount of polymer A corresponding to 0.5% of the clay concentration (i.e. the optimum dose). After 15 seconds of rapid mixing, the suspension was subjected to slow (30 r.p.m.) stirring, using a paddle stirrer. Samples were withdrawn at different intervals directly into the syringe and a filtrability determination was carried out. 

Figure 6.15 The floe volume in shear against the number of particles per floe for a kaolin suspension. Different aggregation numbers for edge-edge and edge-face interactions were achieved by adjusting pH and electrolyte conditions. Face-face interactions were induced by the addition of a monolayer of HDTAB...

Figure 4. Electrophoretic mobility (EM) and residual turbidity for kaolin suspensions (50 mg/L)...

The SEM picture (Fig. 1, insert a) confirms that the main part of kaolin particles has size in the range of 300-600 nm, but the distribution is rather broad. This kind of kaolin with rather fine particles has a high specific surface area and a high negative charge density of — 13.75 C/g. Thus, the kaolin suspension remains stable due the strong electrostatic repulsion between particles. 

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

In one case, multiple pulmonary kaolin granulomata developed secondary to the use of a liquid kaolin suspension for pleural poudrage to treat recurrent spontaneous pneumothoraces, presumably because the kaolin entered the lung through pleuro-alveolar or pleuro-bronchial openings (4). 

The kaolin suspension (kaolin, milk) is partially dewatered by sedimenlalion and filtration... 

Johnson, S.B., Russell, A.S.. and Scales, P.J., Volume fraction effects in shear rheology and electroacoustic studies of concentrated alumina and kaolin suspensions. Colloids Surf. A, 141, 119. 1998. 

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. 

The adsorption of natural polyelectrolytes (serum albumin-BSA) on kaolin suspensions as well as the complex formation with Na-chondroitin-6-sulfate (Na2Chs) was studied by Shimabayashi et al. by means of a microscope electrophoretic apparatus [11]. The iep of kaolin after covering with BSA was determined to be lower than that of BSA itself the zeta potential was positive at pH lower than 4.2. When the pH became higher than the iep, the zeta potential was reversed to negative values and decreased with pH. 

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... 

Stabilization and destabilization studies on kaolin suspensions were performed in our group by means of various electrokinetic methods to follow the adsorption process of differently charged polyelectrolytes. The polyelectrolytes used were polycations such as the branched free polybase polyethyl-eneimine (PEI) and the linear PD ADM AC, and Na-poly aery late as polyanion, whereas the polycations are of different charge density. In Figures 4-7 results of electrophoretic light scattering experiments (Zetasizer 4, Malvern) of 0.05% (w/w) kaolin suspensions are presented (compare Ref. 24). 

First of all, acoustophoresis is a useful method to distinguish between nondispersed and well-dispersed kaolin suspensions. By adding polyanions... 

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

L Jamstrdm, L Lason, M Rigdahl, U Erikson. Flocculation in kaolin suspensions induced by modified starches 2. Oxidized and hydrophobically modified oxidized starch in comparison with poly(vinyl alcohol) and carboxymethyl-cellulose. Coll Surf A 104 207-216, 1995. 

Figure 3.55 Cross-flow electro-filtration of kaolin suspension.

Kaolin and alumina suspensions are also, in some cases, included in water paint formulations. It has been shown in [193] that a maximum shear yield stress is observed with AKP-30 alumina suspensions of a mean primary particle diameter of ca. 0.3 pm at pH 9, independent of the particle volume fraction between 0.2 - 0.3. For kaolin suspensions, the maximum shear yield stress is observed at pH 6 independent of the solid volume fraction. A direct correlation with the electrokinetic potential is observed. Thus, the pair-wise particle interaction is due to the electrostatic interaction which allows to control the stability of these suspensions. 

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