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Environmental Behavior of Mineral Deposits

One of the greatest limiting factors in predicting the geochemical behavior of mine drainage water is the poor understanding of the stabilities of minerals and other compounds that interact with ground and surface waters around mineral deposits. The need for a more thorough knowledge of the stabilities of these compounds is essential (1) for understanding the conditions of formation of acid mine drainage and predicting how climatic variations might change the severity of the problem and (2) for designing effective remediation strategies.

Stability data for a class of compounds known as efflorescent salts are notably limited. Efflorescent salts are highly soluble, hydrated, heavy-metal sulfate compounds that have been shown to be very important for storing heavy metals and acid during dry periods in acid mine drainage settings. During rain storms or spring melting of snow packs, these salts readily dissolve and release large amounts of heavy metals and acid to the watershed. Mineralogical studies by the USGS have identified many of these minerals at study sites in the East.

Compilations of existing data demonstrate that the stabilities of some heavy-metal salts vary systematically and predictably. This observation is being used to estimate stability parameters for compounds for which there is no information. New experimental studies are aimed at verifying the estimation procedures and at measuring stability parameters for compounds that are not amenable to the estimation procedures. Ultimately, the new experimental data will be used to model the chemistry of acid mine drainage waters and their interactions with surrounding rocks and watersheds.

Products

Chou, I-M, Seal, RR, and Hemingway, BS, 1998,

Humidity buffers and their application to studies of dehydration reactions of sulfate salts at 0.1 MPa [abs.]: AGU Transactions, v 79, p S364.

Chou, I.M., Seal, R.R.,II, and Hemingway, B.S., 1998,

Relative humidity-temperature relations of dehydration reactions for hydrated salts: a new experimental approach [abs.]: Geological Society of America, Abstracts with Programs, v. 30, no. 7, p. A-129.

Chou, I.M., Seal, R.R.,II, and Hemingway, B.S., 1999,

Determination of melanterite-rozenite and chalcanthite-bonatite equilibria at 0.1 MPa by using the humidity buffer technique: Goldschmidt Conference, Boston, Aug. 22-27, 1999.

Collaborators

Collaborators include the Department of Energy, Oak Ridge National Lab, and the University of Nebraska