TREATMENT OF PYRITE-GENERATED POLLUTION

Although there have been many reviews of the kinetic paths by which pyrite oxidation produces sulfate and acid, pragmatic tests were necessary to develop practical methods for controlling polution from Skytop roadcuts. Objectives are first to coat pyrite to repress its reactions with both oxygen and water, and second to minimize the concentrations of solutes produced. Needed for these purposes are (1) buffers to neutralize the acidity to pH 6+, (2) added cation concentrations to precipitate excess sulfate, and (3) suspension-stabilizing, viscosity-controlling components to favor the persistence and distribution of slurry additives.

Tests were carried out with slurry treatment in 10 ton tank samples and 50 lb column samples of aggregate from I-99 roadcuts. Additives used were 325 mesh limestone, periclase, and kaolinite in different proportions. Neutralization was achieved routinely with low concentrations of solids. Sulfate control resulted from the precipitation temporaarily of green rust and more persistently of gypsum. Penetration of the aggregate and partial coating of pyrite surfaces depended on clay concentrations. Practical methods of applying the slurry treatment are more challenging than the geochemical problems.