Potential Inhibition of Acid Formation in Pyritic Environments Using Calcium Sulfite Byproduct

Pyrite (FeS 2 ) oxidation in coal mine spoils and coal refuse produces copious amounts of acid that can cause severe environmental damage. Prevention of acid formation by calcium sulfite (CaSO 3 ), a flue gas desulfurization (FGD) byproduct of the scrubbing reaction used to remove sulfur dioxide from flue gases when coal is burned, was studied. First-order rate constants of CaSO 3 oxidation by O 2 ranged from approximately 0.0164 min - 1 (initial pH 8.0, 25 °C, 21% O 2 ) to 0.3807 min - 1 (initial pH 5.0, 15 °C, 21% O 2 ). Overall, the rate constants dramatically increased when the initial pH decreased from 6.5 to 5.0, the temperature increased from 5 to 15 °C, and the O 2 content in air increased from 0.2% to 21%. When 6.4 g of CaSO 3 or 10 g of CaSO 3 -containing FGD byproduct were mixed with 50 g of coal refuse in small columns (2.5 × 13 cm), the total acidity in the leachate water collected during 27 weeks was reduced by 45% and 64%, respectively, as compared to the untreated control. Mixing CaSO 3 with coal mine spoil or coal refuse before extensive oxidation occurs reduces acid production because the CaSO 3 reacts with any O 2 introduced into the spoil or refuse materials before it can react with pyrite to form acid.