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This article in SSSAJ

  1. Vol. 46 No. 6, p. 1321-1325
    Received: Feb 26, 1982
    Accepted: June 24, 1982

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Quantitative Evaluation of Water Adsorption on Soil Clays1

  1. A. D. Karathanasis and
  2. B. F. Hajek2



Quantitative water adsorption determinations were obtained from clay fractions of soil and sedimentary samples by both adsorption isotherms and low temperature thermogravimetry and differential scanning calorimetry techniques. Isotherms at 35°C were obtained with a sealed evacuated quartz spring system and a cathetometer. The weight of water required for monolayer coverage was calculated by application of BET and Langmuir equations. Surface areas based on adsorption by the BET equation were more suitable than from Langmuir, especially when hydroxy-interlayered or zeolite impurities were present. Quantifications of expanding 2:1 minerals by surface area, weight loss, and enthalpy methods compared favorably. Correlation coefficients comparing methods were high (r = 0.97) and average deviations were small (±3.9%). Water adsorbed by clays at 52% relative humidity was exactly double the monolayer BET value. Water vapor adsorption level for montmorillonitic clay fractions was always >9.0%. Monolayer adsorption limits between mixed and kaolinitic mineral classes ranged from 2.2 to 2.4%. These relationships indicate that water adsorption can be used to aid routine clay mineral analysis for classification purposes.

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