Abstract
Iron sulfide minerals commonly found in natural anoxic Fe-S systems have been shown to reductively transform chlorinated hydrocarbons including trichloroethylene (TCE). In the present study, we tested the feasibility of applying an Fe(II) solution to a TCE-contaminated aquifer groundwater under simulated sulfide reducing conditions to enhance reductive transformation of TCE to nontoxic compounds. To achieve this goal, iron sulfide particles were precipitated under a range of pH and Fe:S molar ratios in aquifer groundwater samples from the Dugway Proving Grounds, Utah. Batch tests for abiotic reductive dechlorination of TCE were performed using the precipitates to establish the conditions for most favorable solids for dechlorination. Under all experimental conditions, the solids formed consisted mainly of mackinawite, a tetragonal reduced iron monosulfide FeS1-x. However, the precipitation conditions strongly affected the reactivity of the mackinawite particles formed. The results indicated that addition of Fe(II) to a sulfur-rich groundwater could reduce free sulfide concentration to levels below what is considered inhibitory for biotic dechlorination of TCE, and that higher pH, an Fe:S ratio close to 1, and the addition of citrate produced the most effective mackinawite for abiotic TCE dechlorination.
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