Flocculation of kaolinite due to the attraction of oppositely charged crystal faces

Schofield, R. K.; Samson, H. R.

doi:10.1039/df9541800135

Cited by 341 publications

(147 citation statements)

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“…Two of the samples studied did contain montmorillonite, and these had exchange capacities of 5 and 7 ; therefore they were not included on the plot of exchange capacity and degree of crystallinity is one that would be expected because if the kaolins were disordered in the stacking, then there would be more exposed charged sites for exchange to take place. Schofield and Samson (1955) and others recently have indicated that exchange is due to substitution within the lattice, and that broken bonds are a relatively minor cause of base exchange. Another property that was correlated with degree of crystallinity was surface area, measured by the BET method in square meters per gram.…”

Section: Discussionmentioning

confidence: 99%

Further Correlations of Kaolinite Crystallinity with Chemical and Physical Properties

Murray¹

1959

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

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Previous work has demonstrated that the degree of crystal perfection in kaolinite can be correlated with many physical properties. I n this paper some further relationships are shown, including surface area, base exchange capacity, total percentage of iron and titanium, and high-temperature mullitization. Surface area, base exchange capacity, and the total amount of iron and titanium in the clay increase as the degree of crystal perfection decreases.

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Section: Discussionmentioning

confidence: 99%

Further Correlations of Kaolinite Crystallinity with Chemical and Physical Properties

Murray¹

1959

Clays clay miner. (Natl. Conf. Clays Clay Miner.)

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“…A kaolinite edge develops a positive charge on the acceptance of a proton by the edge hydroxyl group from the solvent (Schofield and Samson, 1954). The reaction may be represented as:…”

Section: Forces Controlling Sediment Volumementioning

confidence: 99%

Mechanism Controlling the Volume Change Behavior of Kaolinite

Rao

Sridharan

1985

Clays and clay miner.

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Abstract--The possible physical and chemical forces controlling the volume change behavior of kaolinite were ascertained from the sediment volume of kaolinite in various solvents under no external load condition and from conventional oedometer measurements of kaolinite in several pore fluids. The minimum sediment volume of 14.5 cmV10 g clay occupied by kaolinite in water where repulsive (R) forces were dominant indicated that the R contribution was insignificant for kaolinite. The maximum sediment volume of 25.0 cmV10 g clay in benzene where coulombic attraction forces were significant suggested that electrostatic attraction between silicate sheets and midplane cations and van der Waals forces were not appreciable for kaolinite. The positive edge-negative face bonding of kaolinite particles in benzene was unlikely because the protons required to impart a positive charge to the edges were not available in the nonpolar solvent. The 3688 cm-l band in the infrared spectrum ofa kaolinite-dimethylamine sample decreased by 10 cm-1 on H-bond formation of the solvent molecule with the exposed structural hydroxyls of the octahedral sheet. The adsorbed solvent molecules likely H-bonded with an adjacent clay particle. That such interparticle H-bonds controlled the sediment volume and interparticle attraction in kaolinite was indicated by the decrease in sediment volume with increase in dipole moment of the solvent molecule, i.e., 25.0 cmV10 g clay in n-heptane (dipole moment,/~ = 0), 23.5 cmV10 g clay in toluene ~ = 0.36), 17.0 cmV10 g clay in ethanol (# = 1.67), and 14.5 cm3/10 g clay in water 0z = 1.84).In the oedometer tests with various pore fluids, a high void ratio (i.e., volume of voids/volume of solids) of ~ 1.3 was obtained for kaolinite in n-heptane, and hexane (u -~ 0) at an external pressure of 1 kg/cm 2 probably because the weakly bonded kaolinite particles were randomly oriented. At the corresponding applied pressure a lower void ratio of 0.88 resulted in water (u = 1.84) where the stronger hydrogen bond between flat layer surfaces of adjacent particles favored a parallel orientation of clay particles.The variations in void ratio-external pressure relationship indicated that kaolinite underwent lower compressibility in a solvent with low dipole moment and vice versa. Thus, the interparticle H-bond did not play a significant role in controlling the shear resistance and volume change behavior. The volume change behavior was essentially controlled by frictional forces and clay fabric. In nonpolar solvents the random arrangement of kaolinite particles and the frictional forces mobilized a high shear resistance on the application of a consolidation pressure, resulting in a lower compressibility. In a solvent with high dipole moment the parallel array of clay particles mobilized less shear resistance and produced a greater compression.

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“…A study of the behavior of kaolinite in suspension has shown that pure Na-kaolinite flocculated at pH < 7 under conditions that dispersed illite and montmorillonite (Schofield and Samson, 1954). The acidified kaolinite retained exchangeable Na, indicating that the clay crystals were negatively charged.…”

Section: Introductionmentioning

confidence: 99%

“…At pH 8, CIwas desorbed from the crystals indicating that the edges were no longer positively charged. Hence, eliminating the positive charges at the edges of the kaolinitic clay plates, dispersed the clay (Schofield and Samson, 1954).…”

Section: Introductionmentioning

confidence: 99%

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Effect of Na-Hexametaphosphate on the Hydraulic Conductivity of Kaolinite-Sand Mixtures

Levy

1991

Clays and clay miner.

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Abstract--Mixtures of kaolinite clay and quartz sand were packed in columns and leached with NaCICaC12 solutions of different concentrations (ranging from 0.5 M to distilled water) having sodium adsorption ratios (SAR) of 5, 10 and 20. Sodium hexametaphosphate (NaHMP) (10 g/m s) was added to each solution. Changes in the hydraulic conductivity (HC) and clay concentration in the effluent were measured, and the dispersion of the clay was evaluated. In the absence of NaHMP, using distilled water instead of 0.01 M solutions caused some reduction in the HC; the reduction became more severe as the SAR increased. At SAR 20 the HC dropped to 73% of that obtained when the 0.5 M salt solution was used. This reduction in HC was related to increases in the pH of the effluent and partial dispersion of the clay. On adding the NaHMP to the leaching solutions, a marked decrease in the HC and severe clay dispersion were observed at all SAR levels, if the kaolinite-sand mixtures were leached with dilute solutions and distilled water. The HC dropped to 40% of that obtained when leaching with 0.5 M salt solution, and dispersed day in the effluent peaked at about l~ in the SAR 20 treatment following leaching with distilled water. The observed reduction in the HC of the kaolinite-sand mixture when NaHMP was added to the leaching solutions was due to the dispersive effect of NaHMP and sodium on the kaolinite. The polyanion NaHMP reduced the edge-to-face particle interactions, thereby enabling the diffuse doublelayer repulsion forces to predominate. Following addition of the polyphosphate, the response of kaolinite to sodium and electrolyte concentration was similar to that reported in the literature for smectite.

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Flocculation of kaolinite due to the attraction of oppositely charged crystal faces

Abstract: Pure kaolinite washed first with 1 M NaCl containing 0.001 M HCI and then with distilled water remains firmly flocculated when salt free. In this state the kaolinite retains exchangeable Na, which shows that the crystals are negatively charged.

Cited by 341 publications

References 0 publications

Further Correlations of Kaolinite Crystallinity with Chemical and Physical Properties

Further Correlations of Kaolinite Crystallinity with Chemical and Physical Properties

Mechanism Controlling the Volume Change Behavior of Kaolinite

Effect of Na-Hexametaphosphate on the Hydraulic Conductivity of Kaolinite-Sand Mixtures

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