taconite n : a variety of chert containing magnetite and hematite; mined as a low-grade iron ore
Taconite is an iron-bearing, high-silica, flint-like rock. It is a Precambrian sedimentary rock referred to as a banded iron formation due to the typical alternating iron-rich layers and shale or chert layers. The very finely dispersed iron content, present as magnetite, is generally 25 to 30%. In the late 19th and early 20th centuries, available iron ore was of such high quality that taconite was considered an uneconomic waste product. After World War II, most of the high grade ore in the United States had been mined out, and so taconite was turned to as a new source of iron. To process taconite, the ore is ground into a fine powder, the iron is separated from the waste rock by using strong magnets, and then the powdered iron concentrate is combined with bentonite clay and limestone as a flux and rolled into pellets about one centimeter in diameter that are approximately 65% iron. The pellets are heated to very high temperatures to oxidize the magnetite (Fe3O4) to hematite (Fe2O3) for further processing. Edward W. Davis is credited with developing this process.
The Mesabi Iron Range region of the American state of Minnesota is a major production area. The taconite iron concentrate is hauled by railroad through Silver Bay, Two Harbors and the Twin Ports of Duluth, Minnesota and Superior, Wisconsin, all on Lake Superior. The ore is generally shipped by lake freighters to other locations on the Great Lakes. Many steelmaking centers are located near Lake Erie. From about 1900 through 1992, great machines called Hulett ore unloaders performed the task. Self-unloading ships later made the Huletts obsolete.
Taconite and Human HealthThe Minnesota Department of Health has launched a study to determine whether taconite fibers and dust can cause or exacerbate lung conditions such as mesothelioma and asbestosis which occur following asbestos exposure. Because asbestos was common in the taconite mining and processing industry, the study will attempt to determine what, if any, influence taconite fibers may have played. This will be the second study of the issue that the MDH has conducted. A 2003 study of taconite miners concluded that the most likely cause of 14 of the 17 cases of mesothelioma was contact with asbestos. However, since the conclusion of that study, 35 additional cases of the disease have been diagnosed. Mesothelioma occurs at twice the expected rate in the region of Minnesota known as the Iron Range.
taconite in Japanese: タコナイト