Stability of copper sulfide in a contaminated soil

Because of their low solubility under reduced soil conditions, metal sulfid es may decrease the toxicity of heavy-metal contaminants. Periodic variatio ns in soil moisture may expose reduced soils to oxidizing conditions that a re conducive to oxidative dissolution of metal sulfides. Using EXAFS spectr oscopy, we determined the proportion of copper sulfide in soil samples befo re 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 bond ing in the first shell, indicating that the soil samples were not oxidized to Cu-O bonding during the treatment.