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The nature of interstratification in mixed-layer illite-montmorillonites has been investigated by comparison of diffraction patterns of ethylene glycol and ethylene glycol monoethyl ether treated samples with calculated one-dimensional diffraction profiles. The calculated profiles take into account the effects of particle size distribution, chemical composition, and convolution factors as well as proportions of layers and interstratification type. On the basis of detailed matching of diffraction patterns of monomineralic illite-montmorillonites of known chemical composition it is concluded that there are three types of interstratification: (1) random, (2) allevardite-like ordering, and (3) superlattice units consisting of three illite and one montmorillonite layers (IMII). By comparison of suites of calculated profiles with the diffraction patterns of many samples of illite-montmorillonites it is concluded that virtually all illite-montmorillonites with expandabilities from about 40 to 100 per cent are randomly interstratified (allevardite being exceptional); at >40 per cent montmorillonite layers they almost always have ordered interstratification. Allevardite-like ordering predominates in illitemontmorillonites which have ordered interstratification, with the IMII superlattice varieties confined to samples with about 10 per cent montmorillonite layers.
The adsorption of CO2 at low temperature (~ -70°C) on thin films of homoionic smectites was studied by X-ray diffraction and by i.r. absorption. An increase in the d001 spacings of these clay films upon adsorption of CO2 was observed. In addition, a dichroic effect was readily discernible by comparing the i.r. spectra at two different orientations of the smectite films; i.e. with the film normal and tilted 35° with respect to the i.r. beam. The CO2 stretching vibration at 2350 cm-1 was used for the i.r. study. These observations conclusively show that CO2 intercalates the smectite structure rather than being adsorbed only in pores between clay tactoids—the limiting process proposed by other investigators.
Adsorption isotherm data from earlier surface area studies are re-examined here through application of the Dubinin equation. Again, intercalation is demonstrated by convergence of the plotted experimental data for smectites containing large monovalent interlayer cations toward a pore volume that is near the calculated theoretical value for a monolayer of intercalated CO2.
Scanning electron photomicrographs of Li- and Cs- smectites provide additional evidence that aggregation differences are not responsible for the large observed difference in BET surface areas obtained for these smectites with CO2 as the adsorbate. At low magnification, visual differences in macro-aggregates are apparent, but at high magnification no significant differences are observed in the micro-structure of individual aggregates where the major amount of gas adsorption really occurs.
Various kaolinites, a dickite and halloysites have been treated by DMSO in presence of D2O and subsequently washed by D2O. This procedure allowed to record OD stretching bands which are due specifically to the intercalated fraction and, for the washed samples, to the fraction of the solid which has been intercalated and has subsequently collapsed.
No structural difference is found between the intercalated materials prepared from the various minerals. Washing usually restores the starting mineral; however, for a non-tubular halloysite, DMSO intercalation and subsequent washing gave a product similar to kaolinite.
Shales from six locations in Oklahoma were subjected to natural weathering for 2 yr. Simulated weathering of these shales was effected in the laboratory by subjecting them to ultrasonic treatment in a tank type device. Both treatments produced disaggregation. X-ray diffraction patterns for the ultrasoni-cally treated and weathered shales indicated no major changes in the types of clay minerals. However, natural weathering in the field produced degradation of the clay minerals in addition to disaggregation of the shales. Ultrasonic treatment appears to be a good predictive test for determining the durability and weatherability of the shales; however, it can simulate field weathering only so far as the engineering index properties of the shale are concerned. It is not a predictive test where the mineralogical characteristics are of significance.
Petrographic studies have shown that brucite is a major constituent of the New Idria serpentinite and of the short-fiber asbestos deposit associated with it. Acid-leaching data suggest that the serpentinite averages 7–8 weight per cent brucite, which contains approximately 15 mole per cent “Fe(OH)2”. Unit cell parameters and electron probe analysis suggest an empirical formula close to (Mg10Fe2)(OH)24 for this phase. Brucite formed during the initial serpentinization of an olivine-rich parent and is concentrated today in the hard, dense serpentinite fragments scattered throughout a highly sheared matrix of soft, friable asbestos. Although brueite is abundant in the fresh serpentinite it is almost absent from the surface weathering zone, which persists to a depth of 20–30 ft across the entire body. Here, serpentinite fragments have oxidized and brueite has transformed in situ into pyroaurite [Mg6Fe2CO3(OH)16.4H2O] and a new mineral, coalingite [Mg10Fe2CO3(OH)24.2H2O]. Brueite in the matrix material has dissolved in the CO2-rich ground waters, yielding soluble magnesium ions and amorphous iron oxides which discolor the surface asbestos.
In the laboratory, samples of fresh serpentinite oxidized and disintegrated completely when exposed to the atmosphere for a few months, due to the brucite-coalingite transformation. In the presence of O2 and CO2, brueite dissolved completely from a water slurry of the serpentinite, yielding a dark brown residue and a clear filtrate which later precipitated hydromagnesite [Mg4(OH)2(CO3)3.3H2O]. These data indicate that in the relatively impervious environment of the residual serpentinite “boulders”, iron-rich brueite oxidizes in air, picking up CO2 and H2O to form coalingite. In the presence of excess ground waters, brueite in the friable matrix dissolves, leaving behind a residue of amorphous iron oxides. Dissolved magnesium ions later precipitate as hydromagnesite, which is also abundant in the surface weathering zone of the serpentinite.
When kaolinite undergoes percussive grinding, pronounced changes take place in its i.r. absorption spectrum even in the earliest stages of the grinding when the lattice is not yet destroyed. In this report, attention is directed to the change in the stretching bands of the hydroxyl ions. A remarkably rapid effect on the band of the intralayer hydroxyl ions has been observed and is attributed to a permanent removal of the protons from these ions. Auxiliary measurements of X-ray diffraction, thermal water loss, and DTA were used to corroborate the spectroscopic evidence for this ready prototropy.
Tubular halloysite from Wagon Wheel Gap, Colorado and spheroidal halloysite from Redwood County, Minnesota were examined by transmission electron microscopy. Clay samples were prepared by the following techniques: drop-mounted suspension on carbon support films; thin sections of clay in Araldite epoxy resin; and carbon-platinum-palladium single-stage replicas.
Both types of dehydrated halloysite have interlayer separations between packets of layers. Halloysite tubes are composed of packets as thin as five layers which sometimes reveal a rolled interior configuration in cross-sectional view. Thicker tubes are composed of many layers per packet. Some large tubes appear in cross section as folded packets of layers. The interior morphology of spheroidal halloysite particles is more irregular and the layer structure is more discontinuous than in most tubes. The spheroidal halloysite of this study is characterized by external tangential plates with hexagonal shape suggestive of kaolinite.
The water adsorption capacity of zeolites is a function of pressure and temperature. Desorption of zeolites may be of three types, wherein the crystal lattice undergoes (1) no or little change, (2) a reversible change, or (3) an irreversible change. In the first two cases, the divariance of the zeolite-water vapor equilibrium results in networks of isobars, isotherms, and isosteres which can be transformed into a “characteristic” curve following the Polanyi-Dubinin theory. Because the volume of the micropores of a zeolite structure is constant, the isotherms and “characteristic” curve can be transformed linearly. During desorption, if the volume of the micropores varies due to a change of structure, the curves show linearity breaks.
On the basis of X-ray diffraction, differential thermal, and thermal gravimetric analyses, the equilibrium curves and structural changes of heulandite and stilbite were determined, using specially designed equipment. In the reversible adsorption range, heulandite shows no linearity breaks in the transforms and no structural variation. Stilbite, however, shows a linearity break in the transforms corresponding to a structural change.
Electrical double layer theory is used to analyze an idealized model unit of a clay particle system with the purpose of describing the mechanical stability in terms of an equilibrium of attractive and repulsive forces. Restricting the analysis to two dimensions, a symmetrical parallelogram formed by four typical clay mineral particles is taken as a representative unit of a flocculated clay and the interactions of mineral faces and associated electrolyte is investigated. The distortion energy of the system thus found is then directly related to the mechanical stability of the model unit’s structure as it varies from parallel to perpendicular orientation. The general pattern of behaviour of the model unit will be shown to be compatible with the mechanical behavior of the clay mass.
The reaction of phlogopite with a trimethylsilylating reagent yielded organosilicate compounds which are soluble in various organic solvents. Gas chromatographic analysis of the soluble products indicates that they consist of the trimethylsilylated derivatives of silicic acids which have been formed in the decomposition of phlogopite by hydrochloric acid and that silicic acids formed by the acid attack are monomelic and also oligomeric. The increase of the ratio of GC peak areas of monomer derivative to dimer one with an increase of the reaction time shows that silicic acids in the reaction system tend to depolymerize. The difference between phlogopite and biotite in the ease of trimethylsilylation also is discussed.
The electron spin resonance (ESR) technique has been used to study the motion and segregation of an organic spin probe cation (4-amino-2,2,6,6-tetramethylpiperidine N-oxide) on K+-hectorite as a function of average surface concentration. The organic cation tends to concentrate in certain interlayers of aqueous hectorite suspensions even when it occupies a small fraction of the cation-exchange sites. This demixing effect is not evident in methanol-solvated hectorite. The average mobility of the probe increases at higher adsorption levels as a result of the shift of the equilibrium in favor of the solution state. Calculated time-averaged orientations of the probe on the clay surfaces are quite different for methanol- and water-solvated systems, emphasizing the importance of the solvent in modifying the surface-cation interaction.
Adsorption studies indicate that paraquat, diquat, and thionine are bound on bentonite by amounts greater than the measured cation-exchange capacity (CEC) of the clay. Methylene blue, new methylene blue, and malachite green are bound by amounts equal to the CEC. The unipositive organocations form aggregates on the clay surface. Aggregation increases with ionic strength and increases the apparent adsorption capacity by 25%. The aggregates are removed by washing with distilled water. Desorption studies show that the dyes are irreversibly bound, whereas the dipositive organocations are reversibly bound. Ionic strength variation reduces adsorption by 15 and 36% in the monovalent and divalent organocation-clay systems, respectively. In the clay-divalent organocation systems adsorption is greater on Na-saturated clay than on K-saturated clay. Adsorption is unchanged over the pH range 4.5–8.5 and decreases steadily below pH 4.0. Changes in adsorption due to changes in temperature are small. The study indicates that ionic strength is the most important variable in clay-organocation interactions.