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• 1 2016-04-25T14:05:14-07:00 Taconite Mining 15 plain 2016-05-03T11:15:54-07:00 By the end of the Vietnam War, most high-grade ores in Minnesota’s Great Lakes region had been depleted, and the industry was forces to consider the benefication (process that removes gangue minerals from ores to produce higher grade concentrate and waste tailings) of lower grade ores. Today, iron ore pellets now account for 97% of U.S. ore production.¹ Rocks with about 50% or more iron are considered natural iron ore, or direct-shipping ore. Lower-grade iron formations are called taconites, which have 25-30% iron content. Taconite is iron-formation that has not been oxidized and enriched by natural processes (source). In addition to the depletion of natural ores through mining, by the end of World War II, blast furnaces had become more efficient in using processed rather than raw ores. Thus, the taconite industry was born. When mining natural ore bodies, there are considerable differences in composition from site to site. These differences are dealt with at the steel mills where various ingredients are added to remove undesired products. Taconites, on the other hand, are mined from large pits which are then blended in the mining, crushing, and concentrating to provide steel mills with a uniform, pelletized product.
  
  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.