Taconite is a low-grade iron ore, containing a relatively small percentage of iron compared to other minerals. This hard, banded sedimentary rock is an important source of iron for steel production, especially as higher-grade iron ore deposits have become less abundant. Its significance grew in the mid-20th century, transforming from a waste product into a valuable resource for the iron and steel industry.
How Taconite Forms and Where It’s Found
Taconite is a variety of banded iron formation, a sedimentary rock characterized by distinct layers of iron minerals interlayered with quartz, chert, or carbonate. These formations contain around 20-30% magnetite, a magnetic iron oxide. Iron in taconite is also present as iron silicates and iron-bearing carbonates.
Geologically, taconite deposits formed billions of years ago during the Precambrian era. These ancient rocks are the result of iron-rich sediments settling at the bottom of prehistoric oceans. Over vast stretches of time, these sediments compacted and solidified, forming the hard rock known today as taconite.
The most significant taconite deposits are found in the United States, particularly within the Lake Superior region. The Mesabi Range in northeastern Minnesota is the largest and most important taconite deposit, extending over 100 miles. Smaller deposits also exist in Michigan’s Marquette Iron Range.
From Rock to Steel: The Taconite Processing Journey
Converting raw taconite into usable iron ore pellets is a multi-stage industrial process due to its low iron content and hard nature. The initial step involves blasting the hard taconite rock into smaller pieces using explosives. These rock fragments are then transported by large electric shovels and massive dump trucks to a processing plant.
At the plant, the taconite undergoes several crushing stages, reducing the rock to pieces approximately the size of a marble. Following crushing, the material is mixed with water and finely ground in rotating mills until it becomes a powder. This fine grinding is important for liberating the iron-bearing particles from the surrounding waste rock, also known as gangue.
Magnetic separation is then employed to extract the iron concentrate from the powdered mixture, as much of the iron in taconite is magnetic magnetite. The non-magnetic waste material is discarded.
The resulting iron concentrate is then combined with binders like bentonite clay and limestone. This mixture is rolled in large rotating cylinders, forming marble-sized balls called green pellets. These green pellets are then fired at high temperatures, around 3,000 degrees Fahrenheit, to harden them for transport and use in steel mills. The finished taconite pellets are rich in iron, containing about 63% to 65% iron.
The Economic Impact of Taconite
Taconite mining and processing have played an important role in the economies of regions where it is found, particularly Minnesota’s Iron Range. The development of taconite processing in the 1950s was important in sustaining Minnesota’s iron ore mining industry after the depletion of high-grade natural ores. This industry contributes to local economies through employment and associated businesses.
The taconite industry provides numerous jobs, including blue-collar, technical, and professional roles. In 2019, Minnesota’s mining industry, largely driven by taconite, contributed over 11,600 jobs, $1.0 billion in labor income, and over $4.0 billion to the state’s economy. This economic activity influences various sectors and creates ripple effects throughout the regional economy. The iron ore produced from taconite is important to the domestic steel industry, with Minnesota alone producing approximately 85% of the iron ore used in American steel production.