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Local View: There is an answer to acid mine drainage concerns

From the column: "It’s still early, but if we work together, it is now possible to see a path forward to restoring damaged waterways and safely mining Minnesota’s rich mineral resources."

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Peter Kuper/Cagle Cartoons
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One of the most vexing issues facing the Northland has been the issue of sulfate produced by past iron mining and proposed copper-nickel mines. Rivers of ink have been spilled over concerns about acid mine drainage and the potential for damage to the Boundary Waters Canoe Area Wilderness — with good reason.

However, an Iron Range company, Clearwater BioLogics, may have solved the sulfate issue in a cost-competitive manner and with valuable byproducts to boot.

Many iron mines pierced sulfur-containing rock formations and the resulting interaction between these sulfur atoms and water formed highly concentrated sulfate compounds in the mine pits. A number of mine pits overrun their banks or seep water out through fault lines. The result is that wild rice beds have been destroyed as bacteria use the oxygen on sulfate for their purposes, and the sulfate is turned into hydrogen sulfide, which is known by its rotten-egg smell. Unless there is a lot of iron in the water, the wild rice withers and dies at sulfate concentrations greater than 10 parts per million.

Many Iron Range communities also use the old iron pits as sources of drinking water. The safe level of sulfate for community drinking water is 250 parts per million. There are a number of communities that far exceed that level.

There are other point sources of sulfate in Minnesota, mainly coal and natural gas-burning power plants such as Minnesota Power’s Boswell and Laskin plants. Oil refineries are also problematic.

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Municipal sewer systems, however, produce sulfate largely based on the sulfate levels found in the drinking water. Cleaning up the drinking water solves that problem.

The technique Clearwater BioLogics utilizes to clean up water is borrowed from nature itself. Using a two-step process, bacteria are fed sulfate-rich iron pit water. The bacteria use the oxygen on the sulfate but produce stinky hydrogen sulfide. The second step uses a weak electrical current through direct reduced iron to create charged iron atoms which bond avidly to the sulfur to create iron sulfide and hydrogen gas. The iron sulfide is heavy and precipitates to the bottom of the vessel for simple removal and use in industry and agriculture. The hydrogen is light and bubbles off as a gas. It is collected and used for everything from electricity to heat and transportation.

The sulfate level through this process is reduced to zero.

The first step, using bacteria in a bioreactor, has been field-tested. The second step, using direct reduced iron (not to be confused with DR-grade iron) has not left the lab bench, but it is a simple electrochemical process which should be scalable. It is believed that the byproducts of the process will nearly pay for the cleanup; however, further research and development is needed, which needs funding through private and public means.

It’s still early, but if we work together, it is now possible to see a path forward to restoring damaged waterways and safely mining Minnesota’s rich mineral resources.

Dr. Eric Enberg practices family medicine in West Duluth and is a member of the Northland Chapter of Citizens' Climate Lobby. He is also a member of the Duluth Climate and Energy Network and Healthcare Professionals for a Healthy Climate.

Dr. Eric Enberg
Eric Enberg

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