Abstract
A smectite has been produced from kaolinite in the temperature range 160°–300°C in liquid water by treatment with silicic acid, calcium oxide, magnesium hydroxide and sodium silicate. The products have been examined by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive analyzer (EDX), transmission (TEM) and analytical transmission electron microscopy (AEM). These data show that the products contain smectite, serpentine, garronite, and wairakite. TEM observations and AEM analyses show that the smectite crystallinity and expandability increases with magnesium hydroxide content. The rate of reaction appears to obey a simple Arrhenius equation with an activation energy of 52.72 kJ mol −1 (12.6 kcal. mol −1). The reaction appears to be sensitive to the quantity of magnesium hydroxide in the starting mixture. Extrapolation to typical soil temperatures of the tropics would indicate conversion times of one year at 100°C, 15 years at 45°C and 54 years at 25°C. These data indicate that beneficiation of highly leached soils by production of smectite clays is slow when treatment involves simple inorganic additives.
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