5:15 PM - 6:30 PM
[MIS12-P06] Crystal growth in clay solidification: zeolitization of smectite
Keywords:smectite, zeolitization, growth rate, volume change
Investigating growth kinetics of zeolite at various solution, temperature and pressure conditions is important to estimate the time-scale of stabilization of clay materials. We conducted alteration experiment of Na-montmorillonite in 1.0 M NaOH at 120 °C and measured dissolution and growth rates by in-situ phase-shift interferometry . The simplified reaction can be scripted as: _Al2Si4O10(OH)2 + 2NaOH = 2NaAlSi2O6(H2O). At this condition, dissolution of montmorillonite proceeds at 6.9E-6 m/s calculated from rate equation  and molar volume. Grown rate of analcime was measured to be 1.1E-10 m/s. Since the reactive surface area of montmorillonite is reducible from 1/10 to 1/1000 by layer-stacking, this observed growth rate of analcime is mostly consistent. However, total volume change of before and after reaction gives 193.96 – 173.91 = +20.05 cm3/mont mol, which suggests that this reaction is suppressed in the limited space. Further, reaction system in the presence of large excess NaOH with a syringe compaction cell produced zeolite as hydro-sodalite scripted as: 3_Al2Si4O10(OH)2 + 20NaOH = Na8Al6Si6O24(OH)2 + 6Na2SiO3 + 12H2O. Its volume change is calculated to be +54.67 cm3/mont mol, which suggests that this reaction can be more suppressed than low-alkaline system. Thus, alkali plays important role for stabilization by zeolitization but this alteration cannot be achieved entirely except at pores.
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