Questions & Answers

How do we move forward with this process?

Minnesotans deserve a thoughtful, informed and respectful discussion about using the state’s precious natural resources – land, water, woods and metals, including copper, the world’s most reusable metal – in a way that protects the environment and brings economic opportunity to Minnesota.

Learn project facts about some of the most-discussed topics surrounding the PolyMet project on


Has copper-nickel mining been done safely before?open

Yes. An example of environmentally responsible non-ferrous mining is next door in Wisconsin. The Flambeau Mine produced copper, gold and silver while protecting the area’s water resources.

  • Closed in 1997, the site has been fully reclaimed and remains an ecologically healthy habitat and community resource visited by thousands or people each year.
  • Despite its positive track record, the project continued to be challenged by environmental groups. Most recently, an appeals court ruled in favor of Flambeau, noting it fully complied with the Clean Water Act. This ruling reversed an earlier decision by a circuit court judge who, despite her ruling, said the mine’s efforts deserved commendation, not penalties, and that the company seemed every bit as committed as the plaintiffs to protect the environment and preserve water quality.

Why does Minnesota need this type of mining?open

Minnesota has one of the world’s largest untapped deposits of copper, nickel and other metals – some 4 billion tons. Copper and nickel are needed not only for everyday living, but also for a green economy that includes wind, solar and other alternative energies. Modern mining techniques make it possible to economically and responsibly mine the state’s rich deposit of these metals – presenting Minnesota with an opportunity for large-scale and enduring economic growth.

What is the difference between ferrous and non-ferrous mining?open

Non-ferrous refers to any mineral or natural material that doesn’t contain iron. Non-ferrous mining typically means mining metals like copper, nickel, cobalt, as well as precious metals, including platinum, palladium, gold and silver.

Does PolyMet’s ore contain sulfur?open

The ore from the PolyMet project contains, on average, less than 1 percent sulfur.

What is sulfide?open

A sulfide is any compound or mineral in which an ion is bonded with sulfur ions. The proposed PolyMet project will mine a metallic sulfide ore – in other words, copper, nickel and precious metals bound together with sulfur ions.

Will PolyMet produce significant amounts of air pollution?open

No. According to the U.S. Clean Air Act, the project will be “a minor source of air pollutants, based on engineering design and modeling.” Emissions of common air pollutants like particulates, sulfur dioxide and nitrogen oxides will be far less than other mining operations, power plants and paper mills.

Will PolyMet generate a lot of hazardous waste?open

No. PolyMet will manage three types of mineral waste from processing (none of which are hazardous): tailings, gypsum and other residues from the hydrometallurgical process.

  • Tailings will be separated from ore using flotation. The tailings do not have the ability to generate acid and will be sent to the existing tailings basin.
  • Limestone will be added to the waste solution to create 99 percent pure synthetic gypsum, which will be sent to the hydrometallurgical cell, unless and until a market for the product can be found.
  • Residue from the hydrometallurgical process, including iron, magnesium and zinc, will be stored in specially constructed hydrometallurgical cells.

Why won’t PolyMet experience the same environmental problems created by non-ferrous mines that operated many decades ago?open

Many years ago, prior to current laws and regulations, mines were largely unregulated and some led to environmental problems. Since then, the government has made substantial changes in regulatory standards. State and federal regulators are reviewing PolyMet’s plan to ensure all activities, including eventual closure, will wisely and responsibly use our state’s rich mineral resources. We will meet these standards by using advanced technology.

Where can I read the SDEIS? open

You can view the complete SDEIS and fact sheets on the Minnesota Department of Natural Resources (DNR) website.

What happens now that the public comment period is over? open

The agencies are reviewing and responding to all comments. Then, they will revise the document and publish a final EIS for public review. The agencies will use this document to make their Record of Decision (ROD) and Adequacy Decision (AD).

After the ROD and AD, the agencies will be able to formally issue permits, each of which will have had its own public process.

Learn how you can support the project and get involved.

When was the SDEIS public comment period?open

The 90-day public comment period was from Dec. 14, 2013, to March 13, 2014.