A Case Study on the Aerobic and Anaerobic Removal of Manganese by Wetland Processes
L.A. Clayton, J.L. Bolis, T.R. Wildeman, D.M. Updegraff, 1997. "A Case Study on the Aerobic and Anaerobic Removal of Manganese by Wetland Processes", 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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Constructed wetlands have been utilized to passively remove metals and raise the pH of acid mine drainage. Manganese is typically the most difficult metal to remove from solution due to the high pH (>8) required to form insoluble manganese precipitates. A study of the removal of manganese by wetland processes was conducted using two guidelines. A microbial ecosystem approach was used to select and test reasonable candidates for passive treatment. Also, a staged design approach consisting of laboratory and bench-scale studies was conducted to examine manganese removal by aerobic versus anaerobic constructed wetland processes. Aerobic laboratory experiments found that common green algae (pond scum) removed large concentrations of manganese from solution and raised the pH through photosynthesis. Aerobic bench-scale reservoirs were constructed containing green algae (predominantly Cladophora) and mine drainage that had passed through an anaerobic constructed wetland, but still contained 32 mg/1 Mn. Static and flow tests were conducted so that manganese was consistently removed to NPDES standards (2 mg/l). Manganese (oxide) coatings on the Cladophora appear to be an important removal mechanism. Four anaerobic bench-scale reactors were constructed, however, only the reactors containing a composted manure substrate achieved manganese removal to the NPDES standard for a significant portion of the experiment. In conclusion, manganese removal from severe acid mine drainage through the use of constructed wetlands requires a two-stage process. An aerobic algal pond appears to be a promising treatment method.
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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