Acid mine drainage in the Iberian Pyrite Belt: 2. Lessons learned from recent passive remediation experiences
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Acid mine drainage in the Iberian Pyrite Belt: 2. Lessons learned from recent passive remediation experiences Carlos Ayora & Manuel A. Caraballo & Francisco Macias & Tobias S. Rötting & Jesús Carrera & Jose-Miguel Nieto
Received: 15 November 2012 / Accepted: 7 January 2013 / Published online: 19 March 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract The Iberian Pyrite Belt (IPB), SW Spain and Portugal, contains about 100 abandoned mine wastes and galleries that release acid mine drainages (AMD) to the Tinto and Odiel rivers. In situ passive remediation technologies are especially suitable to remediate the drainages of these orphan sites. However, traditional remediation systems, designed for coal mines, have been demonstrated inefficient to treat the IPB mine waters. Due to their high acidity and metal loads, large amount of solids precipitate and fast clogging of porosity or passivation (coating) of the reactive grains occurs. To overcome these problems, the dispersed alkaline substrate (DAS) a mixture of finegrained limestone sand and a coarse inert matrix (e.g., wood shavings) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate. The high porosity retards clogging. However, calcite dissolution only raises pH to values around 6.5, at which the hydroxides of trivalent metals (Al and Fe) precipitate, but it is not high Responsible editor: Philippe Garrigues C. Ayora (*) : J. Carrera Institute of Environmental Assessment and Water Research, CSIC, Barcelona, Spain e-mail: [email protected] M. A. Caraballo Department of Geosciences, Virginia Tech, Blacksburg, VA, USA F. Macias : J.-M. Nieto Department of Geology, University of Huelva, Huelva, Spain T. S. Rötting Department of Geotechnical Engineering and Geo-Sciences, Technical University of Catalonia Barcelona, Barcelona, Spain
enough to remove divalent metals. Caustic magnesia (MgO) buffers the solution pH between 8.5 and 10. A DAS system replacing limestone with caustic magnesia has been tested to be very efficient to remove divalent metals (Zn, Cd, Mn, Cu, Co, Ni, and Pb) from the water previously treated with calcite. Keywords Mine water . Passive treatment . Dispersed alkaline substrate . Limestone . Caustic magnesia . Schwertmannite . Hydrobasaluminite . Hydrozincite
Introductory background to conventional passive treatments for mine waters Acid mine drainage (AMD) is a worldwide problem with high environmental and ecological impacts. It is generated by oxidation of metal sulfides and consists of an aqueous solution of sulfuric acid containing metals. Moreover, AMD pollution is well known for its longevity. The release of contaminants can persist for hundreds and even thousands of years after mining activities have stopped (Strömberg and Banwart 1994; Younger 1997). In addition to this problem, it is common to see that most of these AMD sources correspond to abandoned mines, where no liable entity can be found to cover remediation costs. This dis
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