pH-Independent and pH-Dependent Surface Charges on Kaolinite

Bolland, M. D. A.

doi:10.1346/ccmn.1980.0280602

Cited by 72 publications

(27 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Natural kaolinites do, however, have a small cation-exchange capacity, generally < 0.02 mol charge kg-i in chemically pure kaolinites (Talibudeen, 1981;Parfitt, 1978;Sposito, 1984Sposito, , 1989 and thus, the surface properties of kaolinite share characteristics with both oxides and smectites. Weak, cation exchange-type sorption observed in macroscopic studies of kaolinite is generally attributed to two factors: either isomorphic substitution of AI 3 § for Si 4 § in the tetrahedral sheet giving rise to a negative structural charge or contamination by small amounts of2:1 phyllosilicate minerals (Schofield and Samson, 1954;Bolland et al, 1976Bolland et al, , 1980Ferris and Jepson, 1975;van Olphen, 1977;Sposito, 1984;Schindler et ak, 1987;Wieland and Stumm, 1992). Several experimental studies suggest that both factors may contribute to ion exchange (Jepson and Rowse, 1975;Lee et al, 1975;Lim et al, 1980;Talibudeen and Goulding, 1983).…”

Section: Sorption and Sorption Sites On Kaolinitementioning

confidence: 99%

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

O’Day

Parks

Brown

1994

Clays and clay miner.

127

View full text Add to dashboard Cite

Abstract--X-ray absorption spectroscopy (XAS) was used to determine the local molecular environment of Co(II) surface complexes sorbed on three different kaolinites at ambient temperature and pressure in contact with an aqueous solution. Interatomic distances and types and numbers of backscattering atoms have been derived from analysis of the extended X-ray absorption fine structure (EXAFS). These data show that, at the lowest amounts of Co uptake on kaolinite (0.20--0.32 ~mol m-2), Co is surrounded by ~60 atoms at 2.04-2.08 A and a small number orAl or Si atoms (N = 0.6-1.5) at two distinct distances, 2.67-2.72 A and 3.38-3.43/~. These results indicate that Co bonds to the kaolinite surface as octahedrally coordinated, bidentate inner-sphere mononuclear complexes at low surface coverages, confirming indirect evidence from solution studies that a fraction of sorbed Co forms strongly bound complexes on kaolinite. In addition to inner-sphere complexes identified by EXAFS spectroscopy, solution studies provide evidence for the presence of weakly bound, outer-sphere Co complexes that cannot be detected directly by EXAFS. One orientation for inner-sphere complexes indicated by XAS is bidentate bonding of Co to oxygen atoms at two A1-O-Si edge sites or an A1-O-Si and AI-OH (inner hydroxyl) edge site, i.e., comersharing between Co octahedra and AI and Si potyhedra. At slightly higher surface sorption densities (0.51-0.57/~mol m-2), the presence of a small number of second-neighbor Co atoms (average Nco < 1) at 3.10-3.13/~ indicates the formation of oxy-or hydroxy-bridged, multinuclear surface complexes in addition to mononuclear complexes. At these surface coverages, Co-Co and Co-AI/Si distances derived from EXAFS are consistent with edge-sharing between Co and AI octahedra on either edges or (001) faces of the aluminol sheet in kaolinite. Multinuclear complexes form on kaolinite at low surface sorption densities equivalent to < 5% coverage by a monolayer of oxygen-ligated Co octahedra over the N2-BET surface area. These spectroscopic results have several implications for macroscopic modeling of metal ion uptake on kaolinite: 1) Primary binding sites on the kaolinite surface at low uptake are edge, non-bridging AI-OH inner hydroxyl sites and edge AI-O-Si bridging oxygen sites, not Si-OH sites typically assumed in sorption models; 2) specific adsorption of Co is via bidentate, inner-sphere complexation; and 3) at slightly higher uptake but still a small fraction of monolayer coverage, formation of Co multinuclear complexes, primarily edge-sharing with A1-OH octahedra, begins to dominate sorption.

show abstract

Section: Sorption and Sorption Sites On Kaolinitementioning

confidence: 99%

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

O’Day

Parks

Brown

1994

Clays and clay miner.

127

View full text Add to dashboard Cite

show abstract

“…It is also stated by another study that the charge from broken edges and exposed OH planes rather than charge from Al/Si substitution determines the kaolinite CEC, even at zero point charge, and that a high CEC in some kaolinites is found to be due to smectite layers on the surface of the kaolinite crystals [4]. However, it is indicated by other researches that the negative charge on kaolinite cannot be attributed to an oxide-like source only, and the partial dissolution of structural aluminum yielding negatively charged vacant sites must also be considered [5].…”

Section: Introductionmentioning

confidence: 99%

Physicochemical characterization of the retardation of aqueous Cs+ ions by natural kaolinite and clinoptilolite minerals

Shahwan

Akar

Eroğlu

2005

Journal of Colloid and Interface Science

View full text Add to dashboard Cite

The aim of this study was to carry out kinetic, thermodynamic, and surface characterization of the sorption of Cs + ions on natural minerals of kaolinite and clinoptilolite. The results showed that sorption followed pseudo-second-order kinetics. The activation energies were 9.5 and 13.9 kJ/mol for Cs + sorption on kaolinite and clinoptilolite, respectively. Experiments performed at four different initial concentrations of the ion revealed that the percentage sorption of Cs + on clinoptilolite ranged from 90 to 95, compared to 28 to 40 for the kaolinite case. At the end of a 1 week period, the percentage of Cs + desorption from clinoptilolite did not exceed 7%, while it amounted to more than 30% in kaolinite, indicating more stable fixation by clinoptilolite. The sorption data were best described using Freundlich and D-R isotherm models. Sorption showed spontaneous and exothermic behavior on both minerals, with H 0 being −6.3 and −11.4 kJ/mol for Cs + uptake by kaolinite and clinoptilolite, respectively. Expanding the kaolinite interlayer space from 0.71 to 1.12 nm using DMSO intercalation, did not yield a significant enhancement in the sorption capacity of kaolinite, indicating that the surface and edge sites of the clay are more energetically favored. EDS mapping and elemental analysis of the surface of kaolinite and clinoptilolite revealed more intense signals on the surface of the latter with an even distribution of sorbed Cs + onto the surfaces of both minerals.

show abstract

“…The third view is that aluminosilicate gel coatings, rich in silica, may exist on the surface, conferring a negative charge on the basal surface that becomes more negative with increasing pH. It is the variation of these different charge contributions at the basal surfaces and at the edges with pH and ionic strength that is used to account theoretically for the measured changes in electrophoretic mobility, surface charge, and extrapolated yield strength as a function ofpH and ionic strength (Diz and Rand, 1989;Bolland et al, 1980;Rand and Melton, 1977;van Olphen, 1977;Schofield and Samson, 1954). The hydroxyl groups at the plate edges are considered to be the major reactive sites (Morris et al, 1990).…”

Section: Introductionmentioning

confidence: 99%

The Effect of Surface Modification by an Organosilane on the Electrochemical Properties of Kaolinite

Braggs

Fornasiero

Ralston

et al. 1994

Clays and clay miner.

104

View full text Add to dashboard Cite

Abstract--The electrochemical properties of kaolinite before and after modification with chlorodimethyloctadecylsilane have been studied by electrophoretic mobility, surface charge titration, and extrapolated yield stress measurements as a function of pH and ionic strength. A heteropolar model of kaolinite, which views the particles as having a pH-independent permanent negative charge on the basal planes and a pHdependent charge on the edges, has been used to model the data. The zeta potential and surface charge titration experimental data have been used simultaneously to calculate acid and ion complexation equilibrium constants using a surface complex model of the oxide-solution interface. The experimental data were modeled following subtraction of the basal plane constant negative charge, describing only the edge electrical double layer properties. Extrapolated yield stress measurements along with the electrochemical data were used to determine the edge isoelectric points for both the unmodified and modified kaolinite and were found to occur at pH values of 5.25 and 6.75, respectively. Acidity and ion complexation constants were calculated for both sets of data before and after surface modification. The acidity constants, pKat = 5.0 and pKa2 = 6.0, calculated for unmodified kaolinite, correlate closely with acidity constants determined by oxide studies for acidic sites on alumina and silica, respectively, and were, therefore, assigned to pH-dependent specific chemical surface hydroxyl groups on the edges of kaolinite. The parameters calculated for the modified kaolinite indicate that the silane has reacted with these pHdependent hydroxyl groups causing both a change in their acidity and a concomitant decrease in their ionization capacity. Infrared data show that the long chain hydrocarbon silane is held by strong bonding to the kaolinite surface as it remains attached after washing with cyclohexane, heating, and dispersion in an aqueous environment.

show abstract

pH-Independent and pH-Dependent Surface Charges on Kaolinite

Cited by 72 publications

References 14 publications

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

Molecular Structure and Binding Sites of Cobalt(II) Surface Complexes on Kaolinite from X-Ray Absorption Spectroscopy

Physicochemical characterization of the retardation of aqueous Cs+ ions by natural kaolinite and clinoptilolite minerals

The Effect of Surface Modification by an Organosilane on the Electrochemical Properties of Kaolinite

Contact Info

Product

Resources

About