Minnesota Department of Natural Resources is responsible for resource development (e.g. mining) by state constitution, school and university trust fund responsibilities (MN Statute 127A.31). We require mining practices that to the extent practicable minimize adverse impacts on water quality, dust generation, erosion, and watershed hydrology. Since the 1970s, the Division of Lands and Minerals has conducted research related to environmentally sound mining of nonferrous and ferrous minerals, peat, and dimension stone. Research has been conducted in cooperation with University of Minnesota, industry, US Environmental Protection Agency, US Bureau of Land Management, US Army Corps of Engineers, and Western Governors' Association.
Cooperative Environmental Research (CER)
The Minnesota Department of Natural Resources has been conducting laboratory and field rock weathering research since the mid-1970s. This research weathering tests of rocks and tailings associated with nonferrous deposits in Minnesota and methods of mitigation applicable to nonferrous and ferrous mine wastes. Research projects are selected cooperatively based on data needs to support the Lands and Minerals Division environmental review and mine permitting responsibilities. Research project results are reported on in two fiscal year (FY) cycles.
Controlling mercury in taconite stack emissions
The taconite processing industry is Minnesota's second largest emitter of mercury to the atmosphere, surpassed only by coal-fired power generation. For Minnesota to reach its mercury reduction goals, the taconite industry will need to find ways to decrease mercury emissions from its ore processing facilities. The DNR has conducted and funded a variety of research projects on mercury reduction from the taconite industry.
Sulfate released from mining regions (MWRAP)
Iron mining is a source of sulfate to nearby watersheds and has recently become a concern because sulfate reduction processes can increase methylmercury production under certain conditions. Methlymercury accumulates in fish tissues and is responsible for fish consumption advisories in the St. Louis River and in many other lakes and rivers across the state. Beginning in 2007, the DNR began investigating sulfate effects on methlymercury by sampling a wide variety of streams and rivers.
Why are we doing this research?
Until the late 1980's, little research had been done regarding environmentally sound management of wastes from hard rock mines. Due to interest in copper-nickel mining in Minnesota during the 1970s, The Minnesota Regional Copper-Nickel Study was initiated to compile information regarding the environmental and socioeconomic issues related to copper-nickel mining in the state of Minnesota. This research was subsequently adopted by Lands and Minerals and continued in order to inform decisions regarding mine waste management. To some extent, research conducted at mines in other locations can be applied to mining in Minnesota, therefore literature work and site visits are helpful. However, many aspects of environmental problems related to mining are site specific, and must therefore be assessed under conditions occurring in Minnesota (e.g. geology, mining methods, climate, geography, hydrology, and socioeconomic conditions). That is, there are some aspects of environmentally sound mining that are best researched under the conditions expected in Minnesota. In addition, some long-term concerns can only be addressed by long-term experiments and governmental agencies are well suited to conduct studies of such duration. It should be noted that pertinent information can also be gained from monitoring of mine sites and provide insight on operational scale of mine waste management techniques.
Minnesota Department of Natural Resources, Division of Lands and Minerals performs research for the following purposes:
- Prediction of mine waste leachate quality
- Assessment of potential impacts of mining, associated mineral processing, and mine and mineral processing waste leachate, and
- Mitigation of mine and mineral processing waste leachate, and other contaminant release.
This research helps to provide a technical foundation for decisions regarding the environmental review and permitting of nonferrous and ferrous mines.
What have we done?
Leachate Quality from Mine Wastes
Minnesota has an extensive taconite mining industry. The mines, tailings, and waste rock produced from taconite mining cover more than 184 square miles (as of 2009). Despite the vast amount of these wastes, leachate quality problems have been minimal. Studies have been conducted to quantify the sulfate released from a tailings basin and to evaluate ground water quality impacts of disposing taconite tailings in existing open pits.
The Duluth Complex and Ely Greenstone formations of northeastern Minnesota host base and precious metal deposits and prospects. The Duluth Complex contains one of the largest enrichments of copper, nickel, and platinum group metals in the Earth’s crust. Numerous locations in the Duluth Complex are being targeted for mining. Exploration for copper-nickel deposits is also occurring in east Aitkin County in an igneous rock unit that is related to the Duluth Complex. Water quality data have been collected from Duluth Complex waste rock in operational stockpiles, small scale test piles, and dimension stone quarries. Extensive laboratory testing has been conducted to better understand the weathering process of Duluth Complex rock and tailings. Laboratory and field rock weathering tests of Ely Greenstone have also been conducted. Rock weathering tests of rock and tailings from locations outside of Minnesota have previously been conducted with funding from both the MN DNR and US Bureau of Mines.
Evaluation of Predictive Tests
Several static and kinetic tests have been developed for predicting mine waste leachate quality. Static tests base predictions on solid phase analyses, whereas kinetic tests use data from weathering tests of mine waste samples. Insight into static and kinetic test accuracy and interpretation has been gained as part of the MN DNR's testing of rock and tailings from the Duluth Complex and Ely Greenstone. Studies on other rock types have further contributed to our understanding of predictive tests.
Mitigation techniques include methods to prevent mine drainage problems as well as treatment methods for water impacted by mining operations. The degree of mitigation required for mining wastes depends directly upon the potential for problematic mine waste drainage quality at a site. Appropriate methods of mitigation can be designed and optimized based, in part, upon the predicted drainage quality. Methods to prevent mine drainage problems include under water disposal of waste rock and tailings, creating wetlands over tailings, co-disposal of tailings and waste rock, adding alkaline materials to mine waste, and coating reactive surfaces to prevent reaction (microencapsulation).
Treatment can include the use of standard water treatment technologies (active treatment) or newer, lower maintenance options that use natural processes (passive treatment). Minnesota Department of Natural Resources, Division of Lands and Minerals designed a small active treatment plant that treats water from the Hibbing field research site while minimizing operation and maintenance.
The Division of Lands and Minerals has also studied passive systems including wetland treatment, sulfate reducing bioreactors, alkaline treatment beds and the use of covers and liners to control the quantity of water entering or leaving mine waste facilities.
Improving Reclamation with Waste Products
Mine waste is primarily broken or ground rock with little to no organic matter or nutrients. The Division of Lands and Minerals has studied the use of waste products to improve vegetation in reclamation of taconite tailings. These materials have included various types of compost, residue from paper mills, treated solids from wastewater treatment plants (biosolids) and dredge material from Lake Superior. Based on this research, new reclamation procedures have been developed to successfully reclaim coarse taconite tailings.
This is a preferred option for sulfide-bearing mine wastes because it limits access of oxygen to the sulfide minerals present and therefore the reaction of these minerals. The Division of Lands and Minerals has examined this strategy, and modifications of it, in both laboratory and pilot tests. These experiments focused on measuring empirical sulfide oxidation rates and evaluating empirical rates to theoretical rates based on natural oxygen diffusion into water.
The mixing of alkaline solids with acid-producing mine wastes is intended to neutralize acid produced within the mine waste disposal facility. The Division of Lands and Minerals has examined this strategy in laboratory tests initiated in 1988 and in more recent field studies.
Please see the Reclamation Sections' list of publications (249 kb) for more information on the research we have done.