FURTHER REFINEMENT OF THE DAVIS-RITCHIE MODEL OF PYRITE OXIDATION IN GEOLOGIC MATERIALS ASSOCIATED WITH MINING
Fennemore et al. (1998) argued that water content was an important variable, particularly in arid climates, and so they revised the DR model to account for changing humidity. They also assumed that D2 was a variable and solved for it by modeling data from humidity cell tests. Resultant D2 values ranged from 2x10-13 to10-10 m2s-1.
We have developed a numerical code that includes all the refinements suggested by Fennemore et al., but also allows the input of measured, variable particle size distributions of rock materials. Data from humidity cell testing of rocks from metal mines in Washington state and Nevada was modeled assuming the measured particle size distributions of the rock materials used in the tests. Values of D2,which ranged from 10-14 to 4 x 10-12 m2s-1, and averaged 5.45x10-13 m2s-1 were obtained by matching the mass of sulfate leached in the tests and model simulations. This study suggests that D2 values derived from Davis-Ritchie modeling of humidity cell test results may differ significantly depending on whether rock particle sizes are input to the model in a distribution function or as measured size distributions.