Principles of Sulfide Oxidation and Acid Rock Drainage
Oxidation of sulfide minerals releases sulfuric acid and dissolved metals, with iron sulfides pyrite (FeS2) and pyrrhotite (Fe(1−x)S) recognized as the most common acid-forming minerals. Several factors control the oxidation rate including: the oxidant ty
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Abstract Oxidation of sulfide minerals releases sulfuric acid and dissolved metals, with iron sulfides pyrite (FeS2) and pyrrhotite (Fe(1−x)S) recognized as the most common acid-forming minerals. Several factors control the oxidation rate including: the oxidant type, sulfide morphology, microbial action, and trace element contents. Whilst metal sulfides such as galena and sphalerite are less acid-forming, they are typically sources of environmentally significant elements such as Cd, Pb and Zn. Common sulfide oxidation reaction products are metal-sulfate efflorescent salts. Dissolution of these minerals is critical to the storage and transport of acids and metals released upon weathering of mineralized rock or mine wastes. Acid formed by sulfide oxidation can be consumed through reaction with gangue minerals. Neutralization is primarily offered by dissolution of carbonate minerals with calcite and dolomite the most effective. Factors affecting carbonate reactivity include: grain size, texture and the presence of trace elements which can influence a mineral’s resistance to weathering. Silicate minerals such as olivine, wollastonite and serpentinite are recognized as effective longer term neutralizers. Lesser neutralizing potential contributions from phyllosilicates, pyroxenes, amphiboles and feldspars have been reported. Micas, clays and organic matter can temporarily adsorb H+ ions through cation exchange reactions, with gibbsite and ferric hydroxide recognized as offering neutralizing capacity under acidic conditions. Ultimately, the balance of acid producing and acid consuming chemical reactions will determine the production of acid rock drainage (ARD).
A. Parbhakar-Fox (&) School of Physical Sciences, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia e-mail: [email protected] B. Lottermoser Institute of Mineral Resources Engineering, RWTH Aachen University, Wüllnerstrasse 2, 52062 Aachen, Germany e-mail: [email protected] © Springer International Publishing Switzerland 2017 B. Lottermoser (ed.), Environmental Indicators in Metal Mining, DOI 10.1007/978-3-319-42731-7_2
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A. Parbhakar-Fox and B. Lottermoser
Introduction Oxidation of sulfidic mine wastes, and the consequent release of acid drainage is one of the main environmental issues facing the mining industry (Hudson-Edwards et al. 2011). The oxidation of sulfides in rock is a natural process which typically occurs slowly as the Earth’s surface erodes and underlying rock oxidizes (Lottermoser 2010). However, mining operations can greatly accelerate the oxidation process through various activities (e.g., grinding of sulfidic ore, excavation of sulfidic rock), providing paths for water and oxygen that allow the accelerated release of pollutants into surface and groundwater at rates far greater than the downstream environment can sustain without significant ecological effects (Lottermoser 2010). Sulfide oxidation is controlled by several intrinsic parameters including trace element chemistry, morphology, electrochemical fact
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