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Understanding PolyMet’s Proposed Copper Mine


Recently, I visited the proposed PolyMet copper mine and processing facility at Hoyt Lakes. This news-making project may launch a new era of mining on Minnesota’s Iron Range—provided the project is approved through a rigorous environmental review and permitting process.

Hosting my visit were PolyMet’s LaTisha Gietzen, an engineer and fourth generation Iron Ranger, and Brad Moore, a senior advisor of public affairs for Barr Engineering. Moore is a former commissioner of the Minnesota Pollution Control Agency and assistant commissioner of the DNR. Full disclosure here, I know Moore personally and fished and hunted with him.

PolyMet proposes to mine and extract copper, nickel, cobalt and precious metals using a former taconite processing plant on the outskirts of Hoyt Lakes. If you were looking to open a new mine, in some ways you could not pick a better place. Although the company’s two open pits would be new, existing mine pits are nearby. Transportation infrastructure, is in place to transport ore from the mine to the processing plant. The facility is a brownfield site where mining activity has occurred since the 1950s. It includes a roughly four-square mile tailings basin where waste material from processing is permanently stored and the water used in the process is collected and re-used.

PolyMet will mine chunks of ore from the pit and transport them to the plant to be crushed and ground into a fine powder. The powder will be made into a slurry and put in large tanks where the metal-bearing sulfide minerals are separated from fine sand tailings. The tailings will be piped to the tailings basin and the sulfide minerals will be processed into various products. PolyMet can accomplish the crushing and grinding operations using about one-third the capacity of the existing plant. Further processing requires new facilities to be built on site.

The sulfide minerals will be heated in an autoclave, triggering a chemical reaction that will separate in solution copper for further processing, nickel and cobalt hydroxide that will be processed off-site, small amounts of precious metals (platinum, palladium and gold) also processed off site, and a byproduct, gypsum, that may be sold as a secondary product. Further on-site processing will produce 99 percent pure copper plates. Total annual output will be 36,000 tons of copper, 7,700 tons of nickel, 360 tons of cobalt and 7,200 pounds of precious metals.

The downside is the mining and processing will produce waste rock and tailings containing sulfur, because rocks containing copper also contain sulfur. When exposed to air and water, some of the mining wastes could create sulfuric acid—which could become acid mine drainage. Much of the environmental debate surrounding the project is whether PolyMet’s plans will contain the waste and whether the company has adequate bankruptcy-proof financial assurance to cover the cost of clean up if acid mine drainage occurs. PolyMet is in the Partridge River watershed, a headwater tributary of the St. Louis River, which enters Lake Superior at Duluth.

PolyMet plans to contain waste materials and have no acid drainage. About 10 percent of the waste rock at the mine contains higher levels of sulfur. This rock will be stored on a liner until it is returned to one of the pits and flooded with water to stop any acid generation, a process called subaquaeous storage. Tailings from processing with low sulfur levels that are not acid-generating will be stored in the tailings basin, which is designed for containment. The company must meet the state’s financial assurance requirements.

Air emissions from the plant are projected to be a small fraction of those produced in taconite processing and PolyMet must meet all state and federal air quality standards. No wastewater discharges from the mine or the plant are proposed during operations, and any discharge from the proposed mine either during operations or after closure will have to meet the state wild rice water quality standard. Current research indicates that PolyMet mine operations will not increase methylation of mercury in the St. Louis River watershed. While the mine site is located on 6,700 acres Superior National Forest property, PolyMet is purchasing lands for exchange. In order to meet the federal government’s obligations to the tribes, the exchange lands will be located within the 1854 treaty area so tribal hunting, fishing and gathering rights are maintained.

While some critics say the PolyMet project is a threat to the Boundary Waters, the project site is about 20 miles southwest of the wilderness boundary and in a watershed flowing in the opposite direction. However, the project is about 6 miles from Hoyt Lakes and upstream from Colby Lake, the community’s water supply. Gietzen says on-site containment will prevent acid drainage from entering surface or ground water and not have an effect on the town’s drinking water or water wells in the vicinity.

PolyMet has worked on the project’s planning and engineering for five years. Because this is a new mining process—and the first coppermine in Minnesota—the plans and projections are based on extensive testing and computer modeling which becomes a basis for many decisions made during the environmental review.

PolyMet’s draft Environmental Impact Statement (EIS) went through the public comment period, drawing comments from average citizens to the U.S. Environmental Protection Agency. The regulating agencies now must respond to all comments and make changes or provide scientific justification for decisions. When the environmental review is complete—contested aspects of the company’s plans may need to be settled in court— PolyMet can then receive its necessary permits.

The EIS provides needed information for the permitting process. Over a dozen federal and state permits are required before mining begins, including a Section 404 federal wetlands permit, a state Permit to Mine, a state Air Emissions Permit and other permits dealing with water protection, waste disposal and pollution control. Only after the permits are acquired can the project move forward.

Beneath northern Minnesota lies a rock formation called the Duluth Complex, which contains 4.5 billion tons of ore and is considered the world’s second largest source of contained copper and platinum group metals. Exploration of the Duluth Complex is ongoing and other mining proposals are in the works.

Our society requires copper, nickel, and precious metals to make everything from cell-phones and laptop computers to “green” technology such as wind turbines and hybrid cars. The big question is: Should we mine copper in Minnesota, where environmental safeguards are in place, or get it from a less-developed corner of the globe which lacks rules to protect the environment and people?

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