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This article in SSSAJ

  1. Vol. 50 No. 1, p. 251-254
    Received: Dec 24, 1984
    Accepted: Aug 26, 1985

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Evaluating Mineral Dissolution in Laboratory Weathering Experiments Using Leachate Equilibria1

  1. Patrick J. Sullivan,
  2. Andrew A. Sobek and
  3. James P. Rybarczyk2



A laboratory mineral weathering study was completed using pyrite and soxhlet leaching apparatus to demonstrate the application of the GEOCHEM computer model for identifying mineral weathering reactions from nonequilibrium leachates. Crushed crystals of pyrite were continuously leached at approximately 27°C for 144 h. Every 24 h, leachate was removed from the soxhlet and analyzed for pH, ferric Fe, ferrous Fe, SO2-4, Ca, Mg, and silica. Based on the stoichiometry of pyrite oxidation, the GEOCHEM computer model was utilized to calculate leachate pH. By comparing the GEOCHEM calculated pH to the observed leachate pH, it was determined that pyrite oxidation in the soxhlet occurs through a reaction with atmospheric O2 and not with ferric Fe. The results of this study exemplifies the use of geochemical models to help identify and characterize weathering reactions under conditions of nonequilibrium.

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