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Stability of copper sulfide in a contaminated soil.

Because of their low solubility under reduced soil conditions, metal sulfides may decrease the toxicity of heavy-metal contaminants. Periodic variations in soil moisture may expose reduced soils to oxidizing conditions that are conducive to oxidative dissolution of metal sulfides. Using EXAFS spectroscopy, we determined the proportion of copper sulfide in soil samples before and after exposure to more oxidizing conditions for 35 days at pH 6.6 or 7.6. The samples were collected from the reduced zone (47 to 73 and 73 to 101 cm depth) of a contaminated soil and contained about 1,700 mg Cu/kg. In both the original and the treated soil samples, we detected only Cu-S bonding in the first shell, indicating that the soil samples were not oxidized to Cu-O bonding during the treatment.