SIDERITE WEATHERING IN ACIDIC SOLUTIONS UNDER CARBON-DIOXIDE, AIR, AND OXYGEN

Siderite (FeCO3) is found in coal overburden, and is commonly subjected to acidic environments in reclaimed minelands, Manganese commonly substitutes for Fe, and can be present in significant concentrations in the mineral. Siderite was incubated in a solution of either potassium hydrogen phthalate (KHP) or sulfuric acid with an initial pH of 3.0 in environments of CO2, air, or O-2. Iron and Mn release from siderite under varying gaseous environments decreased in the following order: CO2 > air > 0(2). Weathering zones developed that were from 0.39 to 0.85 mm thick. Iron oxides precipitated in the weathering zone and slowed iron release from siderite samples incubated in H2SO4 under all three gaseous atmospheres, Iron oxides did not precipitate in the weathering zone for samples reacted in KHP solution, The release of Fe and Mn to solution followed a zero order reaction rate.