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This article in SSSAJ

  1. Vol. 35 No. 5, p. 714-718
    Received: Feb 9, 1971
    Accepted: May 5, 1971

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Illite Solubility1

  1. R. C. Routson2 and
  2. J. A. Kittrick3



Equilibrium solubilities of the 0.2–2.0µ size fraction of three K+-saturated illites were determined in high-pH aqueous solutions. Beavers Bend, Fithian, and Goose Lake illites were selected for the study. Solubility products were found to be 10-77.6±0.1 for Beavers Bend, 10-76.6±0.3 for Fithian, and 10-76.7±0.2 for Goose Lake illites, based on mean calculated formulae of K0.53 (Al1.66, Fe0.20, Mg0.13) (Si3.62, Al0.39) O10 (OH)2, K0.64 (Al1.54, Fe0.29, Mg0.19) (Si3.51, Al0.49) O10 (OH)2, and K0.59 (Al1.58, Fe0.24, Mg0.15) (Si3.65, Al0.35) O10 (OH)2, respectively. From the solubility product and known thermodynamic relationships, the standard free energy of formation (ΔG) was calculated for each illite. ΔG's were −1267.6±0.9 for Beavers Bend, −1270.6±1.0 for Fithian, and −1265.3±1.0 kcal/gram formula weight for Goose Lake illities.

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