Rates of Iron Sulfide Oxidation in Coal Spoil Suspensions

Abstract

AbstractRates 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.