Siderite Weathering in Acidic Solutions under Carbon Dioxide, Air, and Oxygen

Abstract

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 O2. Iron and Mn release from siderite under varying gaseous environments decreased in the following order: CO2 > air > O2. 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.

Neutralization Potential Determination of Siderite (FeCO3) Using Selected Oxidants

“…The color of precipitates formed after complete oxidation with O 2 and titration with NaOH were dark reddish brown (2.5YR 3/4), suggesting that Fe 2+ was oxidized to Fe 3+ and hydrolyzed to ferrihydrite, lepidocrocite (γ‐FeOOH), or an amorphous Fe oxide during testing. The transformation of FeCO 3 to γ‐FeOOH or α‐FeOOH after oxidation with O 2 is consistent with atmospheric weathering of FeCO 3 under natural conditions (Senkayi et al, 1986; Frisbee and Hossner, 1995).…”

“…Siderite is susceptible to oxidation when exposed to atmospheric weathering conditions, which can be described by Eq. [3] to [6] (Frisbee and Hossner, 1995; Lindsay, 1979). Continued weathering of FeCO 3 produces a neutral reaction when lepidocrocite (γ‐FeOOH) or goethite (α‐FeOOH) is the reaction product.…”

“…[3] to [6] (Frisbee and Hossner, 1995;Lindsay, 1979 Continued weathering of FeCO 3 produces a neutral reaction when lepidocrocite (g-FeOOH) or goethite (a-FeOOH) is the reaction product. Atmospheric weathering conditions favor alteration of siderite to goethite through dissolution and ensuing oxidation or precipitation (Senkayi et al, 1986 (Doolittle et al, 1992;O'Shay et al, 1990).…”

Effect of Peroxide on Neutralization‐Potential Values of Siderite and Other Carbonate Minerals

“…The samples used by Skousen et al (1997) consisted of overburden materials whose mineralogy was determined semiquantitatively by bulk‐sample X‐ray diffractometry. We have extended the work of Skousen et al (1997) and Frisbee and Hossner (1995) by performing standard Sobek tests and additional tests with peroxide for 10 monomineralic specimens of carbonate minerals, including five siderite samples, and all samples were characterized by electron microprobe analyses. The additional compositional quantification has allowed comparisons of the measured versus predicted NP values both before and after addition of peroxide in the NP tests.…”

Minerals and mine drainage

“…Analysis of surfacewater, groundwater, and water samples from the mine workings suggests it is unlikely that groundwater will be affected beyond the mine lease area. Frisbee and Hossner (1995) studied the release of metals from mine overburden. Siderite (FeCO) was found in coal overburden, and is commonly subjected to acidic environments in reclaimed minelands, resulting in release of Fe and Mn.…”