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Rates of Iron Sulfide Oxidation in Coal Spoil Suspensions¹

ABSTRACT

Rates of pyritic coal spoil oxidation were studied in water suspensions of each of two particle-size fractions (< 0.5 mm and 0.5–2 mm). The treatments on each of the size fractions included liming with reagent grade CaCO₃ at rates of 0, 14.4, and 28.8 g kg^–1. In another treatment, toluene was added to unlimed suspensions to inhibit microbial growth.

The greatest rate of salt formation (taken as a measure of pyrite oxidation) was associated with the larger size fraction. Toluene suppressed the oxidation-dissolution rate, suggesting a microbial role in pyrite oxidation in these systems. The application of CaCO₃ at 14.4 g kg^–1 spoil to the 0.5- to 2.0-mm size fraction enhanced the oxidation-dissolution process during the initial phase of the reaction (0–100 min). When the larger size fraction was amended with CaCO₃ at a rate of 28.8 g kg^–1, three rates of oxidation-dissolution were apparent. The first rate was attributed to dissolution of indigenous sulfate salts. The second rate was attributed to oxidation of a more reactive pyrite fraction than that described by the third rate (slowest rate). This last rate was attributed to a nonmicrobial oxidation pathway due to the higher pH values observed in the suspension.

Key Words: mineral dissolution • suspensions • pyrite • sulfate salt formation

¹ Contribution from the Dep. of Agron., Univ. of Kentucky Agric. Exp. Stn., Lexington, KY 40546-0091. The investigation reported in this paper (no. 83-3-44) is in connection with a project of Kentucky Agric. Exp. Stn. and is published with the approval of the Director.

² Assistant extension professor, assistant professor, and senior lab technician, respectively. Dep. of Agron., Univ. of Kentucky, Lexington, KY 40546-0091.

Received for publication November 29, 1983.