REACTION SEQUENCE OF SODIUM MONTMORILLONITE UNDER HYDROTHERMAL CONDITIONS

概要

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The natural Na-montmorillonite (Tsukinuno mine.Yamagate Prefecture, Japan) was treated under hydrothermal conditions.Temperature ranged between 250 and 500℃ at 100MPa, and run durations ranged between 1 and 150 days.The identification of phases was carried out by the X-ray powder diffraction method.The Greene-Kelly test was applied to distinguish among montmorillonite, beidellite and saponite.The phases identified in the products were plotted in a time-temperature diagram.The diagram showed that montmorillonite below 350℃ reacted to the assemblage of mixed-layered phase of smectite and the 1:1 regular interstratification of montmorillonite/beidellite (S/r.i.M-B)+montmorillonite+quartz+analcime, and with increasing temperature transformed to the assemblage of Na-rectorite+quartz+feldspar, through the intermediate phase assemblage of beidellite+saponite+quartz+feldspar.The diagram indicated also that montmorillonite and S/r.i.M-B might be stable clay minerals below 300℃, and that the decomposition of montmorillonite to an assemblage of beidellite, saponite and quartz can proceed in nature below the temperature where rectorite is formed.
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