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Clean Tailing Reclamation Project
1996
2000
Laboratory and greenhouse work performed at Montana State University, Bozeman, MT; field pilot study built in Butte, MT
Project Sponsor(s): Hazardous Substance Research Center for EPA Regions VII and VIII and Montana Department of Natural Resources and Conservation |
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| Conceptual Schematic |
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Project Partners: Montana Resources Inc. (MRI), Butte, MT
Research Objectives:
- Demonstration of an alternative, cost effective, permanent method for tailing reclamation in addition to currently employed methods;
- Reduction of the toxicity, mobility, and bioavailability of heavy metal contaminants in tailing material;
- Reduction of the acid generation potential of tailing material, and consequently the potential for mobilization of heavy metals;
- Establishment of vegetation on tailing materials currently not supporting vegetation;
- Recovery and recycling of economically valuable mineral resources present in tailings as waste minerals and environmental contaminants.
Project History: Acid-producing mine tailings are present at many active and inactive mine sites and pose an environmental liability due to the potential for future acidification caused by pyrite oxidation. Since pyrite has essentially no economic value, it is not recovered during mining resulting in pyrite-bearing tailings following mining. Conventional approaches to reclamation typically involve capping of mine tailings with coversoil followed by revegetation. Alternative methods using soil amendments have been employed for reclamation where coversoil is locally unavailable. Lime can be added to mine tailings to ameliorate acidic conditions followed by revegetation using adapted plant species. The Clean Tailing Reclamation research project proposed an alternative method to sulfide tailing reclamation using reprocessing to remove sulfide minerals in materials used for plant growth. These reclamation methods offer some potential for decreased cost and improved vegetation performance compared with conventional techniques.
Experimental Approach: Acid-producing mine tailings were collected from three sites in western Montana for greenhouse evaluation. Each tailing material was reprocessed to separate heavy sulfide minerals from lighter silicate materials. The resulting silicate fraction constituted approximately 90% of original sample mass while the residual 10% was sulfide-rich and demonstrated elevated levels of metals. The silicate fraction was used as a plant growth media and compared to coversoil and lime treated tailings in a 120 day replicated greenhouse study. Following completion of the greenhouse investigation a field research site was identified at an operational copper mine. Again, replicated experimental plots were constructed using run-of-mine tailings, tailings reprocessed to remove sulfides and locally available coversoil. Each of the plots was subsequently monitored to assess the success of established vegetation.
Results: Reprocessing of sulfide mine tailings was successfully accomplished resulting in substantially decreased levels of pyrite and trace metals in the ‘cleaned’ tailing material that was subsequently used as a plant growth media. Plant vigor and production in both the greenhouse and field study suggests that adequate to excellent vegetation can be established in reprocessed tailings following removal of sulfides.
Supplementary Considerations: Full scale implementation of mine tailing reprocessing has occurred in several locations within the U.S. and Canada, principally with the goal of mineral recovery. The opportunity for using mineral processing to facilitate land reclamation has been largely overlooked. While this project has demonstrated the potential for using reprocessed or de-pyritized tailings as a plant growth media the overall deployment of this technology is dependent on economics. It appears unlikely that small sites can be reclaimed using this technology owing to expenses incurred related to mobilization of the mineral processing equipment to remote sites. Conversely, many large operational mines have all the equipment necessary to perform the work on site and performing the sulfide mineral separation step is only a simple modification of the waste stream. Conceptually, an active mine site could switch to “cleaned” tailings during the final phase of mining, therein capping their tailing impoundment with what would amount to clean sand. The challenge of revegetation of the cleaned tailings, subsequently, would be comparatively simple and related to the addition of nutrients and organic matter rather than costly neutralizing amendments to combat sulfide oxidation and acid generation.
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| Greenhouse experimentation using cleaned tailings, coversoil, lime amended tailings and a control with no amendments. |
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| Pyrite and sulfides being removed from tailing material using a shaker table (pyrite is the dark mineral moving diagonally toward the lower left on the table; lighter silicate minerals wash over the ridges and are captured at the bottom of the photo). |
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| Slurried tailings being run through spiral classifiers to separate sulfides and silicates at the field site. Since the gravimetric density of pyrite is nearly twice that of silicate minerals, particles of equal size can be separated gravimetrically. |
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| Cleaned tailings are regraded to form test plots for experimentation. |
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| All test plots exhibited a strong response to the addition of organic matter. The image shows the impact of compost addition during the first growing season on the run-of-mine tailing test plot. |
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| Plants innoculated with mycorrhizae were nested in the experimental design to evaluate the effect of mycorrhizae collected from different sources on the experimental treatments. |
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Stuart Jennings
Reclamation Research Unit
106 Linfield Hall
Montana State University
Bozeman, MT 59717
(406) 994-4821
stuartj@montana.edu
Krueger, J.M. 1997. Clean Tailing Reclamation: revegetation of Mill Tailings Following Removal of Pyrite and Heavy Metals. M.S. Thesis, Montana State University, Bozeman, MT.
Jennings, S.R., Krueger J. M., Seastone Moynahan, O. and C. Zabinski. 2000. Clean Tailing Reclamation. Reclamation Research Unit Publication No. 2000-4, Montana State University, Bozeman, MT.
Stuart Jennings
August 2004 |
