Acid‐Base Properties of a Limed Pyritic Overburden during Simulated Weathering

Abstract

AbstractSurface‐mine reclamation is often hindered by the formation of acid minesoil and acid mine drainage from FeS2 oxidation. Surface soils containing FeS2 are often treated with crushed limestone (predominately CaCO3) to prevent acid minesoil formation. The main objective of this study was to evaluate the long‐term effectiveness of liming pyritic minesoil to prevent the formation of acid minesoil and acid mine drainage. Pyritic minesoils that did not receive lime became acidic very rapidly and produced acidic leachate. Almost all of the FeS2 in this treatment oxidized during the first 200 d. The addition of lime at a rate of 25% of the theoretical acid‐base account (ABA) significantly slowed FeS2 oxidation, but rapid oxidation ensued after the added lime was neutralized. Treatments receiving a liming rate of 50% ABA or greater remained neutral to alkaline throughout the study. Acid‐base values and residual FeS2‐CO3 data, however, indicate that the lime was dissolving from the system faster than the FeS2 was oxidizing, and all the treatments would eventually become acidic. The results indicate that the liming of a pyritic overburden to an ABA of 125% is not a sustainable solution to preventing acid minesoil and acid mine drainage.