The Nature of the Surface Charge of Kaolinite

Zhou, Zhipeng

doi:10.1346/ccmn.1992.0400320

Cited by 151 publications

(93 citation statements)

References 17 publications

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“…As with Braggs et al (1994), a short equilibration time in the experiments of Schindler et al (1987) is a possible explanation of a lower p.z.n.p.c. Zhou and Gunter (1992) did not report an equilibration time but their titration data indicate p.z.n.p.c. --< 5 for kaolinite KGa-1, similar to the results in the present study.…”

Section: Points Of Zero Chargementioning

confidence: 97%

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Surface Charge Properties Of Kaolinite

Schroth

Sposito

1996

MRS Proc.

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-The surface charge components of 2 Georgia kaolinites of differing degrees of crystallinity (KGa-1 and KGa-2) were determined using procedures based on charge balance concepts. Permanent structural charge density (tr0) was determined by measuring the surface excess of Cs, which is highly selective to permanent charge sites. The values of cr0 determined were -6.3 -~ 0.1 and -13.6 ---0.5 mmol kg -~ for kaolinites KGa-1 and KGa-2, respectively. The net proton surface charge density (trn) was determined as a function of pH by potentiometric titration in 0.01 mol dm -3 LiC1. Correction from apparent to absolute values of cr n was made by accounting for A1 release during dissolution, background ion adsorption and charge balance. Lithium and C1 adsorption accounted for the remainder of the surface charge components. Changes in surface charge properties with time were measured after mixing times of 1, 3 and 15 h. the latter representing "'equilibrium". Time-dependenl behavior is believed to be caused by mineral dissolution followed by readsorption or precipitation of A1 on the mineral surface. Both the point of zero net charge (p.z.n.c.) and the point of zero net proton charge (p.z.n.p.c.) changed with mixing time, generally increasing. The "'equilibrium" p.z.n.c, values were approximately 3.6 for KGa-1 and 3.5 for KGa-2, whereas the corresponding p.z.n.p.c, values were about 5.0 and 5.4. The p.z.n.c, results were in good agreement with previous studies, but the values of p.z.n.p.c, were higher than most other values reported for specimen kaolinite.

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Section: Points Of Zero Chargementioning

confidence: 97%

“…Samples (0.2 kg) of 2 specimen kaolinites, KGa-i and KGa-2, described as "well crystallized" and Copyright 9 1997, The Clay Minerals Society 85 Zhou and Gunter (1992) ~ i.e.p. = pH value at which electrophoretic mobility = 0. p.z.n.p.c.…”

Section: Stock Suspensionsmentioning

confidence: 99%

Surface Charge Properties Of Kaolinite

Schroth

Sposito

1996

MRS Proc.

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“…The charge on the edges is due to the protonation -deprotonation of surface hydroxyl groups. It depends on the solution pH (Zhou & Gunter 1992). Zhang et al (1987) pointed out that at the edges, especially at the concave margin of broken crystals of kaolinite, the charge is positive, and hence kaolinite can adsorb a complex Au ion with a negative charge.…”

Section: Interaction Between [Au(hs 2 )]mentioning

confidence: 99%

THE ADSORPTION OF [Au(HS)2] ON KAOLINITE SURFACES: QUANTUM CHEMISTRY CALCULATIONS

Hong¹,

Fu²,

Min³

2001

The Canadian Mineralogist

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Electronic structure and energies of the system of [Au(HS) 2 ]-adsorbed on an atomic cluster of kaolinite were calculated using the self-consistent-field discrete-variation (SCF-X ␣ -DV) method. A hexagonal ring of SiO 4 tetrahedra with three Al octahedra, including 38 atoms, was used -ion and kaolinite is expected to be strong. This kind of adsorption can be regarded as the formation of a surface complex.

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“…Based on the consideration of surface charge density, Zhou and Gunter (1992) noted that the ionization of edges alone can not explain the magnitude of the changes in the CEC with pH. Thus, they concluded that the basal surface must also contribute to these charges.…”

Section: Ph Control On Cecmentioning

confidence: 99%

“…McBride (1989) proposed that isomorphous substitution in kaolinite generates about 0.01 mol Kg 1 of permanent charge but gave no details. The attribution of surface charge in kaolinites to isomorphous substitution is called the Constant Basal Surface Charge model (Zhou and Gunter, 1992). Bolland et al, (1976) concluded that most of the negative surface charge on kaolinite is pH independent and is likely to be due to isomorphous substitution.…”

Section: Introductionmentioning

confidence: 99%

Cation Exchange Capacity of Kaolinite

Eggleton

1999

Clays and clay miner.

301

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Abstract--Experimental cation exchange capacities (CEC) of kaolinites were determined and compared to theoretical calculations of CEC. The comparison reveals that the exchangeable cations occur mostly on the edges and on the basal (OH) surfaces of the mineral. It also shows that permanent negative charge from isomorphous substitution of AP + for Si 4+ is insignificant. The CEC of kaolinite strongly depends on the particle size (both thickness and diameter in the (00l plane) and pH value. Particle size is more important than crystallinity in affecting kaolinite CEC. This study shows that the hydroxyls on the exposed basal surfaces may be ionizable in aqueous solutions. The amount of negative charge on the edges and the exposed basal hydroxyls depends on pH and other ion concentrations. A higher pH value gives rise to more negative charges, which lead to a higher CEC value. This study indicates that charge from broken edges and exposed OH planes rather than charge from A1/Si substitution determines the kaolinite CEC, even at zero point charge. A high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals.

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The Nature of the Surface Charge of Kaolinite

Cited by 151 publications

References 17 publications

Surface Charge Properties Of Kaolinite

Surface Charge Properties Of Kaolinite

THE ADSORPTION OF [Au(HS)2] ON KAOLINITE SURFACES: QUANTUM CHEMISTRY CALCULATIONS

Cation Exchange Capacity of Kaolinite

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