Nancy Schuldt, photo from
Nancy Schuldt, photo from

Historically Minnesota’s lands have been mined for its iron deposits, as taconite mining. Extraction of precious metals would be part of the state’s first sulfide mine. The impact of mining on environmental resources, locally and globally, has not been good — with destruction of usable land, toxic watershed spills, higher rates of mercury found in children, and long and expensive environmental clean ups. Cloquet-based biologist and aquatic ecology scientist Nancy Schuldt is a Fond du Lac Water Projects coordinator who specializes in toxicity research and watershed hydrologic modeling. She offered this perspective on the science behind the environmental concerns. 

Q: How is the newly proposed copper-nickel (sulfide) mining different from Minnesota’s existing iron ore (taconite) mines? 

Sulfide mining extracts precious and strategic minerals, like copper, nickel, silver, and gold, from the Earth’s rock and sediment. Chemically these minerals are bound with sulfur within the rock, thus the term ‘sulfide ore.’ When the ore is blasted and crushed, sulfide is released and exposed to air and water. Upon exposure, the sulfide waste becomes sulfuric acid, a compound highly toxic to humans and aquatic life. The process also releases dissolved heavy metals, such as mercury, in toxic concentrations.

Taconite is a low-grade, iron-bearing ore that is similarly blasted and crushed, and then concentrated to make higher-grade iron pellets used for steelmaking. 

Both types of mining create footprints of permanently destroyed habitat and leave waste in the form of tailings [waste rock that has been blasted and separated from precious metals], contaminated water, air toxins, and dust. The wastewater of sulfide mining is more toxic than taconite mining, but taconite wastewater is also polluted. 

Q: Are there processes to clear pollutants and contaminants from wastewater and rock?

Wastewater is recycled in plant processing, then slurried into a basin, where it seeps out of purposefully “leaky” tailings dams to ensure structural stability. Tailings basins themselves are considered “treatment systems,” to avoid certain requirements, but the only treatment they provide is some settling of the fine tailings solids. 

Q: What protections prevent leaks?

Minntac has installed collection systems outside the dams, and is pumping seepage back into the tailings pond, but they only capture about 50 percent. PolyMet proposes to install seepage collection systems outside the tailings dam, but claims of nearly 100 percent capture are not supported by evidence.