Revealed: The U of M’s “top-secret” research on reducing mine waste

December 2, 2014

Jennifer Martin-Romme
Zenith News

Two sources familiar with the University of Minnesota’s “top-secret” research on a method for removing sulfate from mining waste have revealed details of the project.


The Zenith has granted these sources anonymity because one is not authorized to speak to the press, and naming the second one would identify the first.


The two-year experiment is conducted in part by UMD’s Natural Resources Research Institute (NRRI) and funded by a $500,000 MNDrive grant, aimed at putting university research to work for industry.


Partners include the Iron Range Resources and Rehabilitation Board, the Minnesota Pollution Control Agency (MPCA), PolyMet Mining, Barr Engineering, and Cliffs Natural Resources. ••see full list


Their goal was to “create a commercial-scale, remotely-operated modular bioremediation system to reduce sulfate,” according to a press release last July.


More recently, NRRI got tight-lipped with the Duluth News Tribune, saying they hope to seek a patent. “University officials won’t say where [NRRI] is overseeing research on whether bacteria can eat enough sulfate to clean up mining waste, calling it only an ‘undisclosed’ flooded mine pit” [“Sulfate-eating bacteria could cut mine waste,” November 17].


But the Zenith’s sources say sulfate-reducing bacteria is not the key factor in the experiment, which began in late 2013 at a 50-year-old mine pit northeast of the proposed PolyMet site near Hoyt Lakes.


The big secret? Floating bioreactors that use an iron compound called “siderite” to reduce sulfate levels dramatically—but with one doozy of a bad side effect: They produce methylmercury.


Sulfate is a byproduct of (among other things) mining ore. It’s produced by taconite mining, and it’s dogged potential copper mining projects like PolyMet. When released into the watershed, sulfate initiates two dangerous chemical reactions:


•It converts to sulfide, which damages wild rice. MPCA has a sulfate standard of 10 milligrams per liter for discharge into “wild rice waters.” (MPCA is currently deciding which specific waters in the state should be considered “wild rice waters.”)


•When sulfate is combined in an anaerobic (oxygen-less) environment with carbon, mercury, and sulfate-reducing bacteria, it causes mercury to “methylate,” which allows mercury to be absorbed by cellular tissues. MPCA has no methylation standard for sulfate discharge, even though one in ten babies born along the North Shore now have dangerously high levels of mercury in their blood.


NRRI Director Rolf Weberg says the current research has only concluded its first phase. The second phase, which started at the end of July and will continue until next summer, is intended to look at byproducts, including methylmercury.


“That’s the whole point of the research: What are the side issues we need to look at? We don’t have peer-reviewed data. We have data that’s promising in terms of reduction of sulfate, but the second phase addresses viability.”


The floating bioreactors look like large swim rafts, but instead of buoys underneath, there are anaerobic containers four to five feet below the freeze line.


They capture water and mix it with a slurry of sulfates, dissolved organic carbon, iron siderite, and sulfate-reducing bacteria. Just add the mercury that’s been in our water for 150 years (called “legacy mercury”) and all the elements of methylation are present.


Over two to three months, the sulfate becomes sulfide, which binds with the siderite, producing harmless iron sulfide. But siderite doesn’t stop mercury methylation. It doesn’t even eliminate sulfates; it brings them down to 200 milligrams per liter—below the standard for discharge into non-wild rice waters, but nowhere near the 10 mg/L standard for wild rice.


Weberg says the reactors would likely be supplemented by other methods, such as reverse osmosis or bioremediation, which would then be less costly if the sulfate levels have already been reduced. “We’re not looking at just one method to get it done...It’s much more affordable to use a less energy-intensive method. Having more than one bullet is a good idea.”


Powered by solar panels, the bioreactors could be quite expensive. A PowerPoint designed by one of the research partners describes the experiment’s first year and extrapolates it to Mesabi Nugget’s Pit 1, which would need 5,800 bioreactors covering 6.5 acres.


The units will require maintenance, replacement parts, and replenishing the substances they consume, particularly large volumes of siderite. Mesabi Nugget, for example, would require an extrapolated seven tons of siderite per day.


And siderite don’t come cheap—$500,000 to $2.5 million for enough to treat one million cubic meters of water containing 1,000 mg/L of sulfate. For the eight million cubic meters per year at Mesabi Nugget, the siderite alone could cost $19.2 million a year.


Weberg says the final model may or may not rely on siderite and cost estimates will be addressed in Phase II of the study.

••The full list of project collaborators, according to a PowerPoint by Laurentian Vision Partnership, includes Laurentian Vision Partnership, the Iron Range Resources and Rehabilitation Board, the East Range Joint Powers Board, the Natural Resources Research Institute/Coleraine Minerals Research Laboratory, Apex Engineering, PolyMet Mining, Barr Engineering, Pace Analytical Services, Northeast Technical Services, Cliffs Natural Resources, Premier Plastics, Silicon Energy, the University of Minnesota, the Minnesota Pollution Control Agency, the Minnesota Trade Office, Clearwater Layline, LLC, Minnesota’s Materials Management Division Cooperative Purchasing (Environmentally Responsible Purchasing), and Industrial & Environmental Concepts, Inc.

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