Geochemistry of Acid Mine Waters
D. Kirk Nordstrom, C.N. Alpers, 1997. "Geochemistry of Acid Mine Waters", The Environmental Geochemistry of Mineral Deposits: Part A: Processes, Techniques, and Health Issues Part B: Case Studies and Research Topics, G.S. Plumlee, M.J. Logsdon, L.F. Filipek
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There are about a dozen major hydrogeochemical processes that can account for the chemical composition of most natural waters. One of these is the oxidation of pyrite, a process at least as important a source of sulfate in natural waters as seawater and sea spray, gypsum dissolution, and atmospheric emissions. The natural process of pyrite oxidation is fundamental to the supergene alteration of ore deposits, the formation of acid-sulfate soils, and the development of acidity and metal mobilization in natural waters. As mineral deposits continue to be mined, and inactive or abandoned mines with their associated waste-rock and tailings piles continue to be exposed to weathering, large concentrations of sulfate and heavy metals will continue to be found in both surface waters and ground waters. Nearly 5 × 1010 tons of mining and mineral processing wastes had been generated in the United States as of 1985 and about 109 tons continue to be generated each year (U.S. Environmental Protection Agency, 1985). A more recent estimate indicates that there may be more than 500,000 inactive or abandoned mine sites in the U.S. (Lyon et al., 1993). Hazardous mine sites in serious need of remediation are probably much fewer but may still range in the thousands. Inventories of mineral resources, mine sites, and their associated environmental hazards are being assembled at various scales by federal and state agencies to better assess the magnitude of the problem.
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The Environmental Geochemistry of Mineral Deposits: Part A: Processes, Techniques, and Health Issues Part B: Case Studies and Research Topics
Environmental issues have become important, if not critical, factors in the success of proposed mining projects worldwide. In an ongoing and intense public debate about mining and its perceived environmental impacts, the mining industry points out that there are many examples of environmentally responsible mining currently being carried out (e.g., Todd and Struhsacker, 1997). The industry also emphasizes that the majority of mining-environmental problems facing society today are legacies from the past when environmental consequences of mining were poorly understood, not regulated, or viewed as secondary in importance to societal needs for the resources being extracted. On the other hand, environmental organizations (e.g., Mineral Policy Center, 1999) point to recent environmental problems, such as those stemming from open-pit gold mining at Summitville, Colorado, in the late 1980s (see Summitville summaries in Posey et al., 1995; Danielson and Alms, 1995; Williams, 1995; Plumlee, 1999), or those associated with a 1998 tailings dam collapse in Spain (van Geen and Chase, 1998), as an indication that environmental problems (whether accidental or resulting from inappropriate practices) can still occur in modern mining. Recent legislation imposing a moratorium on new mining in Wisconsin, and banning new mining in Montana using cyanide heap-leach extraction methods further underscore the seriousness of the debate and its implications for mineral resource extraction.
In this debate, one certainty exists: there will always be a need for mineral resources in developed and developing societies. Although recycling and substitution will help meet some of the worlds resource needs, mining will always be relied upon to meet the remaining needs. The challenge will be to continue to improve the ways in which mining is done so as to minimize its environmental effects.
The earth, engineering, and life sciences (which we group here under the term “earth-system sciences,” or ESS for short) provide an ample toolkit that can be drawn upon in the quest for environmentally friendly mineral resource development. The papers in this two-part volume provide many details on tools in the scientific toolkit, and how these tools can be used to better understand, anticipate, prevent, mitigate, and remediate the environmental effects of mining and mineral processing.
As with any toolkit, it is the professional’s responsibility to choose the tool(s) best suited to a specific job. By describing the tools now available, we do not mean to imply that all of these tools need even be considered at any given site, nor that