Taconite Mining
In basic terms, the taconite process involves crushing the mined rock down to a fine grain, and then mechanically removing the iron minerals from the waste material (source). Magnetite is removed from the waste materials via large electromagnets. Hematite requires a more selective process called flotation. After the concentration of the iron minerals, they are washed to remove any fine dust. The remaining fine powder of iron minerals is then formed into pea-sized pellets that are readily available for transport and use in blast furnaces. These taconite pellets are formed by adding small amounts of bentonite clay and water to the iron concentrate, which binds the iron particles together. This mixture is then tumbled through large cylinders to produce round pellets that are hardened by firing.
In the 1940s, the magnetic separation technique was developed to pelletize the taconite. The waste from this process, known as tailings (silicate and carbonate minerals) are slurried with water and disposed of. In the case of Reserve Mining, the company used Lake Superior water for this process as well as a disposal site. When Reserve was at full capacity, it contributed 11% of the total U.S. iron production and 25% of Minnesota’s taconite pellet production.
1-"Iron Mining Today." Iron IV. Accessed April 26, 2016. http://geo.msu.edu/extra/geogmich/iron_iii.html.