Stability of Montmorillonites: I. Belle Fourche and Clay Spur Montmorillonites1
- J. A. Kittrick2
Seven samples of montmorillonite from Belle Fourche, South Dakota and one from Clay Spur, Wyoming were equilibrated with various solutions for 3 to 4 years. Most samples did not exhibit a static equilibrium, yet solution compositions moved along or toward definite solubility lines in relation to pH-⅓ pAl3+ vs. pH4SiO4 axes. This behavior was not altered by a wide variety of sample treatments, including two particle-size fractions. The approach from both undersaturation and supersaturation indicated that true equilibria were involved.
Periodic analyses of the equilibrating liquid gave a range in pAl3+ of 2.44 to 4.26, in pH4SiO4 of 2.48 to 3.47, and in pH of 2.74 to 3.60. Analyses were also made for Mg, Na, and Cl-.
A montmorillonite-kaolinite mixture established the montmorillonite-koalinite join and demonstrated montmorillonite-kaolinite equilibria. The solution composition of several other samples helped define an experimental Belle Fourche-Clay Spur montmorillonite solubility line. The slope and intercept of this line on pH-⅓pAl3+ vs. pH4SiO4 axes agreed with a calculated slope and intercept that were based upon the premise that the solubility of montmorillonite is independent of the exchangeable ion.
A ΔG of −2468.5 ± 0.3 kcal per mole was calculated for Belle Fourche and Clay Spur montmorillonites, based upon the assumption that Fe3+ in solution was controlled by hematite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © .