Effectiveness of the addition of alkaline materials at surface coal mines in preventing or abating acid mine drainage--Part 1. Geochemical considerations

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Abstract

The addition of alkaline materials to supplement deficient "neutralization potential" (NP) of mine spoil, and thus to prevent or abate acid mine drainage, has riot been successful at most surface coal mines in Pennsylvania. A basic problem may have been improper accounting for acid‐production potential and thus inadequate addition rates of calcium carbonate (CaCO3 ), calcium oxide (CaO) , or calcium hydroxide [ Ca (OH)2 ] at many mines. The commonly used acid‐base accounting method is based on the following overall reaction:

FeS2 + 2 CaCO3 + 3.75 O2 + 1.5 H2O --> Fe(OH)3 + 2 SO4-2 + 2 Ca+2 +2 CO2(g),

where the acidity from 1 mole of pyrite (FeS2) is neutralized by 2 moles of CaCO3 . This method presumes that gaseous carbon dioxide (CO2) will exsolve, and therefore may underestimate by up to a factor of 2 the quantity of CaCO3 required to neutralize the "maximum potential acidity" (MPA) in the mine spoil. This paper reviews some geochemical reactions involving FeS2 and various alkaline additives that support the argument that the acid‐base accounting method for computing MPA from overburden analyses should be revised. Considering the stoichiometry of the following overall reaction:

FeS2 + 4 CaCO+ 3.75 O2 + 3.5 H2O --> Fe(OH)3 + 2 SO4-1 + 4 Ca+2 + 4 HCO3-,

4 moles of CaCO3 are required to neutralize the maximum potential acidity produced by the oxidation of 1 mole of FeS2 . Therefore, the multiplication factor for computing MPA from the overburden sulfur concentration, in weight percent, should be increased from 31.25 to 62.5.

Publication type Conference Paper
Publication Subtype Conference Paper
Title Effectiveness of the addition of alkaline materials at surface coal mines in preventing or abating acid mine drainage--Part 1. Geochemical considerations
Year Published 1990
Language English
Publisher West Virginia University Publication Services
Publisher location Morgantown, WV
Contributing office(s) Pennsylvania Water Science Center
Description 10 p.
Larger Work Type Conference Paper
Larger Work Subtype Conference Paper
Larger Work Title Proceedings of the 1990 Mining and Reclamation Conference and Exhibition
Conference Title 1990 Mining and Reclamation Conference and Exhibition
Conference Location Charleston, WV
Conference Date April 23-26, 1990
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