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TECHNICAL REPORTS
Ecosystem Restoration

Iron Sulfide Oxidation as Influenced by Calcium Carbonate Application

^a Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843
^b Plant Science Dep., South Dakota State Univ., Brookings, SD 57007

^* Corresponding author (l-hossner{at}tamu.edu)

Received for publication March 5, 2002. Two overburden materials, with different FeS₂ contents (1.9 and 4.1%) and low acid neutralization potential, were limed with CaCO₃ at rates of 0, 25, 50, 75, 100, and 125% based on the amount of CaCO₃ needed to provide an acid–base account deficit (A/B_a) of zero (A/B_a = neutralization potential - potential acidity - exchangeable acidity). The limed overburden materials were inoculated with Thiobacillus ferrooxidans and leached weekly with deionized water. Residual FeS₂ and CaCO₃ were determined in samples over a 378-d period. Oxidation followed zero-order kinetics with respect to FeS₂ concentration at pH values greater than 4 and first-order kinetics at pH values less than 4. Zero-order oxidation rates ranged from 0.0l to 0.46 µmol g^-1 d^-1 in the overburden with 1.9% FeS₂ and from 0.01 to 0.22 µmol g^-1 d^-1 in the overburden with 4.1% FeS₂. Oxidation following the first-order rate law had a first-order rate constant of 0.03 d^-1 in the 1.9% FeS₂ overburden and 0.01 d^-1 in the 4.1% FeS₂ overburden. The calculated half-life was 23 d for the 1.9% FeS₂ overburden and 69 d for the 4.1% FeS₂ overburden. Additions of CaCO₃ affected FeS₂ oxidation by controlling the pH of the system. Liming to greater than 50% of the acid–base account deficit did not significantly affect the zero-order oxidation rate. Dissolution of the applied CaCO₃ was found to be faster than the oxidation of FeS₂ at pH values greater than 4. It was projected that at lime rates up to 125%, the CaCO₃ would dissolve and leach out of the system before all the FeS₂ oxidized, leaving the potential for acid minesoil formation.

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This Issue in Journal of Environmental Quality

JEQ 2003 32: 745-750. [Full Text]  

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