Potential inhibition of acid formation in pyritic environments using calcium sulfite byproduct

Pyrite (FeS2) 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 (CaSO3), 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 CaSO3 oxidation by Oz ranged from approximately 0.0164 min(-1) (initial pH 8.0, 25 degrees C, 21% O-2) to 0.3807 min(-1) (initia1 pH 5.0, 15 degrees 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 degrees C, and the O-2 content in air increased from 0.2% to 21%. When 6.4 g of CaSO3 or 10 g of CaSO3-containing FGD byproduct were mixed with 50 g of coal refuse in small columns (2.5 x 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 CaSO3 with coal mine spoil or coal refuse before extensive oxidation occurs reduces acid production because the CaSO3 reacts with any O-2 introduced into the spoil or refuse materials before it can react with pyrite to form acid.