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Soil Science Society of America Journal Abstract -

Temperature and Water Activity as Variables in Soil Mineral Activity Diagrams1


This article in SSSAJ

  1. Vol. 44 No. 1, p. 149-154
    Received: Dec 12, 1978
    Accepted: Sept 25, 1979

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  1. S. V. Mattigod and
  2. J. A. Kittrick2



Thermochemical data are available for many soil minerals and solutes for calculating temperature dependent equilibria. These equilibria can then be used to construct temperature dependent activity diagrams, which are necessary for studies of chemical weathering of soil minerals under wide ranging temperature conditions. Such an activity diagram was constructed for the K2O-Al2O3-SiO2-H2O system. The diagram indicated, for example, that between 25–95°C, the kaolinite-gibbsite equilibrium changes over a four-fold increase in Si(OH)40 concentration. The diagram further predicted that the equilibrium solubility of quartz changes roughly five-fold and that of amorphous silica changes nearly three-fold within the same range of temperature. It was also shown for the same four component system that the change in activity of water significantly alters the thermodynamic stability relationships between various minerals. It appears that the activity of water is an important variable in activity diagrams applied to chemical weathering studies of minerals in arid and salt affected soils and sediments.

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