Transformation Of Montmorillonite Research Articles

Release of Mg and Fe From the Octahedral Sheets During the Transformation of Montmorillonite Into Kaolinite

AbstractIsomorphous substitutions of Mg and Fe for Al generally appear in the octahedral sheets of montmorillonite, whereas they are infrequent in kaolinite. Therefore, the release of Mg and Fe from the octahedral sheets probably happens during the transformation of montmorillonite into kaolinite, which could affect the migration of Mg and Fe from clay minerals into surrounding environments. The objective of the current study was to investigate the relationship between Mg and Fe release during the transformation of montmorillonite into kaolinite. The results showed that the d060 value of clay minerals decreased slightly, and the intensities of both the AlMg–OH and AlFe–OH bending vibrations also decreased gradually. In addition, the (Mg+Fe)/Al (major octahedral ions) atomic ratio of kaolinite was lower than that of montmorillonite, especially in identical hydrothermal products. These results indicated that Mg and Fe ions were released progressively from the octahedral sheets during the transformation of montmorillonite into kaolinite. Moreover, the changed relative concentrations of Mg and Fe ions in the supernatant solutions after hydrothermal reactions suggested a random distribution of Mg and/or Fe in the octahedral sheets of the montmorillonite. These results improve understanding of the release relationship between Mg and Fe during clay mineral evolution and of the distribution of these two ions in the octahedral sheets, as well as the chemical composition of clay minerals as an indicator of geological environments.

Fe microenvironments in heat treated rare-earth exchanged montmorillonites

The rare-earth bentonites were prepared from Ca-bentonite by suspending Ca-bentonite in rare-earth (Ce, La, Y) perchlorate solution. 57Fe Mössbauer spectra of rare earth montmorillonites before heat treatments showed a doublet envelop at room temperature, reflecting dominantly Fe3+ assigned to (cis) octahedral site in the montmorillonite. At the same time, the 80 K spectra of these rare-earth exchanged montmorillonites revealed an additional magnetically split component, too, associated with iron atoms intercalated in the interlayer space. In the case of heat treated samples (250 °C, 360 °C and 500 °C for 4 h), a new doublet component associated with Fe3+ at trans octahedral site, appeared in both the 295 K and 80 K Mössbauer spectra. Powder X-ray diffractometry (XRD) measurements of the heat treated rare earth montmorillonites revealed that a gradual mineral phase transformation of montmorillonite to muscovite occurred upon the applied heat treatments, being consistent with the completing electron magnetic resonance (EMR) and Mössbauer spectroscopy (MS) results.

Genesis and transformation of minerals in the formation of red (Alfisols) and black (Inceptisols and Vertisols) soils on Deccan basalt in the Western Ghats, India

SUMMARYSix noncalcareous pedons from the basaltic terrain of the Western Ghats in Maharashtra, India, were identified for the present study. Of these, two red‐soil pedons (Typic Haplustalfs) and one black‐soil pedon (Vertic Ustropept) are from the Bhimashankar plateau at an elevation of 1000 m above mean sea level, experiencing a humid (>5000 mm rainfall) tropical climate. The other three pedons of black soils (Typic Chromusterts and Typic Ustropept) are from the semi‐arid zone (500–1000 mm rainfall), at an elevation of 825–893 m.Clay mineralogical investigation indicated that interstratified smectite‐kaolin (Sm/K) is dominant in red soils whereas smectite is dominant in black soils. The Sm/K is formed by the transformation of montmorillonite, the first weathering product of Deccan basalts in a humid tropical climate. We suggest that the interstratification of kaolin with chloritized smectite may also be an important ephemeral stage during the transformation of smectite to kaolinite. The presence of zeolites provided sufficient bases to prevent the complete transformation of Sm/K to kaolinite. The presence of smectites and zeolites made the formation of black soils possible in microdepressions even in a tropical humid climate. The genesis of Sm/K and smectite in red and black soils, respectively, suggests that these soils formed through a progressive landscape reduction process. The presence of both Sm/K and smectite in black soil clays of semi‐arid climate suggests that the smectite of these soils was formed in an earlier humid climate.

Relations Between Maturation of Organic Matter and Geothermal Effect, As Exemplified in Canadian East Coast Offshore Wells

ABSTRACT The integration of microscopic and chemical studies of organic matter from several offshore wells of Eastern Canada results in the definition of a maturation index. This parameter is based on the state of preservation scale, but its value is an average of all available data reflecting evolution. The use of this maturation index apparently improves the representativity of the results obtained in the appraisal of organic metamorphism. The systematic comparison of the curves established on a regional scale by means of the maturation index, the rate of sedimentation and the temperature from well-logging, displays a conspicuous relation between maturation, time and the geological history of the section. Conversely, the present variations of the geothermal gradient do not seem to influence the evolution of organic matter to a large extent. It appears that the beginning of the window corresponds to a degree of organic diagenesis more advanced in sediments more recently buried. This finding demonstrates that there is a compensation effect between temperature and overburden time. An obvious correlation also exists between incipient oil genesis and the transformation of montmorillonite into illite and mixed-layered minerals. It can thus be assumed that the thermal effect causing maturation is conjugated with a mechanical effect due to the compaction of sediments resulting in the expulsion of fluids. Therefore the most favourable conditions for sediments to release liquid hydrocarbons seem to occur when this stage (i.e. incipient diagenetic zone) has been reached.

SOME FEATURES OF ALTERATION IN CLAY MINERALS RELATIVE TO OIL FORMATION

A study of the distribution of clay minerals and their accessories in the Mesozoic and Tertiary sediments of the Caucasus area points to the conclusion that the replacement of montmorillonite by hydromicas is necessarily associated with the conversion of dispersed organic matter to petroleum. The hydromicatization reaction gives off energy which may promote the conversion of organic matter. The transformation of montmorillonite also contributes to the migration of the broken-down organic compounds, inasmuch as the sorption is much weaker on hydromica than on montmorillonite.—Auth.