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Brunet, J. - F. (2000). Drainages miniers acides; contraintes et remedes; etat des connaissances--Acid mine drainage; problems and remediation techniques; state of the art. Principaux Resultats Scientifiques – Bureau de Recherches Geologiques et Minieres, 1999/2000, 97–98.
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Cravotta, C. A., III, & Trahan, M. K. (1999). Limestone drains to increase pH and remove dissolved metals from acidic mine drainage. Appl. Geochem., 14(5), 581–606.
Abstract: Despite encrustation by Fe and Al hydroxides, limestone can be effective for remediation of acidic mine drainage (AMD). Samples of water and limestone (CaCO3) were collected periodically for 1 a at 3 identical limestone-filled drains in Pennsylvania to evaluate the attenuation of dissolved metals and the effects of pH and Fe- and Al-hydrolysis products on the rate of CaCO3 dissolution. The influent was acidic and relatively dilute (pH < 4; acidity < 90 mg) but contained 1-4 mg . L-1 of O-2, Fe3+, Al3+ and Mn2+. The total retention time in the oxic limestone drains (OLDs) ranged from 1.0 to 3.1 hr. Effluent remained oxic (O-2 > 1 mg . L-1) but was near neutral (pH = 6.2-7.0); Fe and Al decreased to less than 5% of influent concentrations. As pH increased near the inflow, hydrous Fe and Al oxides precipitated in the OLDs, The hydrous oxides, nominally Fe(OH)(3) and Al(OH)(3), were visible as loosely bound, orange-yellow coatings on limestone near the inflow. As time elapsed, Fe(OH)(3) and Al(OH)(3) particles were transported downflow. The accumulation of hydrous oxides and elevated pH (> 5) in the downflow part of the OLDs promoted sorption and coprecipitation of dissolved Mn, Cu, Co, Ni and Zn as indicated by decreased concentrations of the metals in effluent and their enrichment relative to Fe in hydrous-oxide particles and coatings on limestone. Despite thick (similar to 1 mm) hydrous-oxide coatings on limestone near the inflow, CaCO3 dissolution was more rapid near the inflow than at downflow points within and the OLD where the limestone was not coated. The high rates of CaCO3 dissolution and Fe(OH3) precipitation were associated with the relatively low pH and high Fe3+ concentration near the inflow. The rate of CaCO3 dissolution decreased with increased pH and concentrations of Ca2+ and HCO3- and decreased Pco(2). Because overall efficiency is increased by combining neutralization and hydrolysis reactions, an OLD followed by a settling pond requires less land area than needed for a two-stagetreatment system consisting of an anoxic limestone drain and oxidation-settling pond or wetland. To facilitate removal of hydrous-oxide sludge, a perforated-pipe subdrain can be installed within an OLD. (C) 1999 Elsevier Science Ltd.
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Dillard, G. (2000). A win-win way to clean up by changing ionic state, new process can precipitate heavy metals. Pay Dirt, 734, 10–11.
Keywords: acid mine drainage; California; chemical composition; companies; environmental analysis; environmental management; heavy metals; ion exchange; ions; metal ores; metals; mining; pollutants; pollution; precipitation; processes; remediation; soils; surface water; United States; water treatment 22, Environmental geology
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Dunn, J., Russell, C., & Morrissey, A. (1999). Remediating historic mine sites in Colorado. Min. Eng., 51(8), 32–35.
Abstract: This article provides examples of reclamation and remediation in Colorado watersheds. The projects were undertaken by the US Environmental Protection Agency (EPA) Region 8, in cooperation with the Colorado Division of Minerals and Geology (CDMG), Colorado Department of Public Health and Environment (CDPHE), US Forest Service (USFS), the Bureau of Land Management (BLM), Bureau of Reclamation (BOR) and the US Geological Survey (USGS). These agencies collaborated on the environmental problems at abandoned mines. These samples involved the interaction of surface and ground waters with sulfide-bearing rocks, mine workings and surface mine spoils that produce acid solutions charged with heavy metals that are toxic to organisms. In these examples, acid mine drainage from historic mines in Colorado has been approached cooperatively with stakeholders. Each example emphasizes one aspect of the three-stage process. These stages include characterization and prioritization, hydrologic controls and the evaluation of long-term remediation activities.
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Earley, D., III, Schmidt, R. D., & Kim, K. (1997). Is sustainable mining an oxymoron?.
Abstract: Sustainable mining is generally considered to be an oxymoron because mineral deposits are viewed as nonrenewable resources that are fixed in the crust. However, minerals are conserved and recycled by plate tectonics which continually creates and destroys ore deposits. Though it is true that rock cycles have much longer periods than biomass cycles, the crust is essentially an infinite reservoir so long as we continue to invest in mineral exploration and processing technology. Implicit in the definition of sustainable development is the recognition that human development of resources in one reservoir may subsequently degrade resources supplied by another. The depreciation of overlapping and adjacent resources is often externalized in the cost to benefit accounting and cannot be sustained if the integrated cost/benefit ratio is greater than 1. The greatest obstacle to sustainability in mining is the expanding scale of excavation required to develop leaner ores because this activity degrades connected resources. In the case of open pit, sulfide ore mining the disturbed land may produce acid rock drainage (ARD). Because ARD will self-generate over the course of tens to hundreds of years the cost of controlling this pollution and rehabilitating mined lands is large and often spread over many generations. Secondary production of minerals from partially excavated deposits where there are preexisting environmental impacts and mine infrastructure help to reduce the risk of depreciating pristine resources, provided that new mining operations “do no (additional) harm” (Margoles, 1996). In turn, a percentage of the profits derived from secondary mineral production can be used for rehabilitation of the previously mined lands. These lands contain significant, albeit low grade, metal concentrations. These concepts are being developed and tested at the Mineral Park Sustainable Mining Research Facility where an in situ copper sulfide mining field experiment was conducted. Monitoring data and computer modeling indicate that ARD is not generated after closure. This is because the ore is not disturbed and is left saturated, whereas unsaturated conditions generate acidic drainage. The short term risk of groundwater contamination is mitigated by utilizing an exempt mine pit to capture any leach solutions that are not intercepted by the wellfield. Using green accounting techniques and transfer models it can be communicated that this mining scenario is an approach to sustainability.
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