The Results of X-Ray and Microscopical Examinations of Soil Colloids

Hendricks, S. B.; Fry, William H.

doi:10.1097/00010694-193006000-00003

Cited by 96 publications

(18 citation statements)

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“…Somewhat more birefringent than 5, index of a few grains higher than 1.56 but most were lower than 1.56. Experiments 7,8,9. Moderate birefringence, mean index about Patterns of the products of experiments 14 and 23 are reproduced in figure 2.…”

Section: Microscopical Examination Of Productsmentioning

confidence: 88%

Hydrothermal synthesis of kaolinite, dickite, beidellite, and nontronite

Ewell¹,

Insley²

1935

J. RES. NATL. BUR. STAN.

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Kaolinite was synthesized by heating coprecipitated AJ20 3-Si02 gels and mixtures of Al20 3 and Si02 with water in a pressure bomb at 310 0 C. Similarly dickite was prepared by treating coprecipitated Ah03-Si02 gels at 350 0 C and 365 0 C, beidellite from mixtures of Ab03 and Si02 at 350 0 C and 390 0 C, and also from co precipitated gels and kaolinite at 390 0 C. Nontronite was madc by treating a coprecipitated Fe203-2Si02 gel at 350 0 C. Beidellite was formed in these experiments in the presence of soda by transport of Si02 in solution to the Alz03 and reaction with Al20 3 in situ.The products were identified by X-ray patterns. Their optical properties were also consistent with those of the natural minerals. The stability ranges of kaolinite, dickite, and beidellite probably occur in the order named, with increasing temperature. This relation between kaolinite and dickite is consistent with geological evidence as to their formation in nature.

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Section: Microscopical Examination Of Productsmentioning

confidence: 88%

Hydrothermal synthesis of kaolinite, dickite, beidellite, and nontronite

Ewell¹,

Insley²

1935

J. RES. NATL. BUR. STAN.

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“…Shortly thereafter, soil chemists applied x-ray diffraction to soil clays and discovered the existence of, and delineated the structures for, the major classes of phyllosilicate clays commonly found in soils (11,12). Soon after it was demonstrated that most phyllosilicates in soils had a permanent negative charge resulting from substitution of lower valence cations in both the tetrahedral and octahedral layers (13).…”

Section: Reactive Mineral Phases In Soils: An Historical Viewmentioning

confidence: 99%

Characterization of complex mineral assemblages: Implications for contaminant transport and environmental remediation

Bertsch

Seaman

1999

Proc. Natl. Acad. Sci. U.S.A.

115

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Surface reactive phases of soils and aquifers, comprised of phyllosilicate and metal oxohydroxide minerals along with humic substances, play a critical role in the regulation of contaminant fate and transport. Much of our knowledge concerning contaminant-mineral interactions at the molecular level, however, is derived from extensive experimentation on model mineral systems. Although these investigations have provided a foundation for understanding reactive surface functional groups on individual mineral phases, the information cannot be readily extrapolated to complex mineral assemblages in natural systems. Recent studies have elucidated the role of less abundant mineral and organic substrates as important surface chemical modifiers and have demonstrated complex coupling of reactivity between permanent-charge phyllosilicates and variable-charge Fe-oxohydroxide phases. Surface chemical modifiers were observed to control colloid generation and transport processes in surface and subsurface environments as well as the transport of solutes and ionic tracers. The surface charging mechanisms operative in the complex mineral assemblages cannot be predicted based on bulk mineralogy or by considering surface reactivity of less abundant mineral phases based on results from model systems. The fragile nature of mineral assemblages isolated from natural systems requires novel techniques and experimental approaches for investigating their surface chemistry and reactivity free of artifacts. A complete understanding of the surface chemistry of complex mineral assemblages is prerequisite to accurately assessing environmental and human health risks of contaminants or in designing environmentally sound, cost-effective chemical and biological remediation strategies.

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“…The clay minerals are layer-type aluminosilicates, ubiquitous on our planet in geologic deposits, terrestrial weathering environments, and marine sediments (1,2). Their name derives from the micrometer-sized particles into which they crystallize.…”

mentioning

confidence: 99%

Surface geochemistry of the clay minerals

Sposito

Skipper

Sutton

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

681

438

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Clay minerals are layer type aluminosilicates that figure in terrestrial biogeochemical cycles, in the buffering capacity of the oceans, and in the containment of toxic waste materials. They are also used as lubricants in petroleum extraction and as industrial catalysts for the synthesis of many organic compounds. These applications derive fundamentally from the colloidal size and permanent structural charge of clay mineral particles, which endow them with significant surface reactivity. Unraveling the surface geochemistry of hydrated clay minerals is an abiding, if difficult, topic in earth sciences research. Recent experimental and computational studies that take advantage of new methodologies and basic insights derived from the study of concentrated ionic solutions have begun to clarify the structure of electrical double layers formed on hydrated clay mineral surfaces, particularly those in the interlayer region of swelling 2:1 layer type clay minerals. One emerging trend is that the coordination of interlayer cations with water molecules and clay mineral surface oxygens is governed largely by cation size and charge, similarly to a concentrated ionic solution, but the location of structural charge within a clay layer and the existence of hydrophobic patches on its surface provide important modulations. The larger the interlayer cation, the greater the inf luence of clay mineral structure and hydrophobicity on the configurations of adsorbed water molecules. This picture extends readily to hydrophobic molecules adsorbed within an interlayer region, with important implications for clay-hydrocarbon interactions and the design of catalysts for organic synthesis.

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The Results of X-Ray and Microscopical Examinations of Soil Colloids

Cited by 96 publications

References 0 publications

Hydrothermal synthesis of kaolinite, dickite, beidellite, and nontronite

Hydrothermal synthesis of kaolinite, dickite, beidellite, and nontronite

Characterization of complex mineral assemblages: Implications for contaminant transport and environmental remediation

Surface geochemistry of the clay minerals

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