There was a time when the steel mills of America belched forth fire and forged more steel than elsewhere on the planet. In those days the mills devoured high grade and continued to do so until there was little left. Many of these minerals were extracted from the hills of Minnesota.
The demand for steel in the Second World War and Korean War was so great that the supplies were severely depleted. In a thirteen year period between 1941 and 1953 more than 850 million tons of iron ore were shipped into the mills. Proven reserves in the Minnesota hills fell from 1.1 billion tons in 1940 to just 8.3 million tons in 1954. Industrialists had to develop a way to exploit low grade supplies.
Their answer came from the work of Edward W Davis (May 8, 1888 to December 1973). Davis was an academic at the University of Minnesota. In 1911 he completed a degree in electrical engineering at Purdue University and moved to Minnesota as a mathematics instructor. From 1913 he worked on the problem of economically extracting iron ore from taconite.
In many respects Professor Davis was ahead of his time. In 1870 vast taconite deposits were discovered throughout Minnesota. The great Misabi Range deposits extend for 110 miles with a width of one to three miles and a depth of up 500 feet. As long as high grade ores were available these were cast aside. Taconite is a hard, flint-like rock which contains a low-grade iron ore and is difficult to process. Professor Davis spent 43 years perfecting that process. He foresaw the time when the industry would have need the low grade ores.
In 1946 Professor Davis took out a patent to convert taconite into iron ore. In the same year the Reserve Mining Company announced plans to develop a new plant at Silver Bay that would ultimately be named in hour of the Professor. In 1955 the Professor was able to patent the full taconite pellet process. One year later the first plant entered into full scale production. From that point, the industry went from strength to strength. By 1979 there were seven companies producing the taconite pellets in Michigan and the industry employed 16,000 people.
Professor Davis deserves to be better known. His efforts caused a renaissance in the Minnesota mining industry. Although industry seemed to decline in the 1970s it has rebounded vigorously since 2005 fuelled by an increased demand for steel in China. Despite the recession, Minnesota still produces 80% of the iron ore that is used to make steel in the United States. While the pall of recession still looms above the smoke stakes at the time of writing, in autumn 2009 the mines made the first tentative steps to return to full production.
The Hull-Rust-Mahoning Open Pit Iron Mine is the king of all mines. It is the largest open cast mine in the world. In 2008 it produced 8.2 million tons of taconite pellets which is a significant part of the total US demand. The scale is truly spectacular. Dumper trucks larger than houses appear insignificant in its vaults. Here, at the epicentre of the taconic industry, in the nearby town of Hibbing, Bob Dylan spent his youth.
Some aspects of mining are obvious. The mineral has to be extracted. Very often this involves the rock into small pieces and scooping up the remnants. Then the rocks are transported for processing. Large dump trucks are used at the Hust Rust Mine. Each dump truck can hold 240 tons of crushed rock. The loading shovel can carry 85 tons of rock in each scoop. At the processing plant the rock is treated so that the ore is concentrated. Ore from the taconite mine has to be transformed into pellets. Then the concentrate is shipped to the consumers. The taconite pellets are loaded onto ore ships which sail the Great Lakes to the steel towns of Gary, Indiana, Cleveland and Ohio.
Actually, this belittles the task. Teasing out the iron required all of Professor Davis’ ingenuity and the best part of his career.
Taconite is a very hard rock. Drilling the holes to blast out the rock was not straightforward. The Professor invented a special jet piercer, or high temperate flame thrower for the purpose.
The iron found within the ore in very low concentrations that are very finely dispersed. The rock typically contains 20 30% iron by weight. The rock has to crushed to a dust before it can be even processed. First the rock is crushed down to the size of marbles. Then the rock is mixed with water and ground to a fine powder in rotating mills.
Then rock is processed. Whereas most minerals are processed chemically Professor Davis decided to use his electrical engineering skills and extract the iron using magnetism. The unmagnetic waste is syphoned off into tailing lagoons.
The next stage is to produce the pellets. The iron rich concentrate is mixed with clay and limestone in large drums. Marble sized balls form when the drums rotate. These are heated until white hot and then allowed to cool. Using pellets allows the product can be transported safely and easily. Steelmakers approve because the pellets are a uniform product which improves their control over the steel making process. The pellets contain about 65% iron by weight and are suitable for direct use in a blast furnace.
Sadly there is a final sting in the tale of Edward W Davis. In 2007 the Minnesota Department of Health decided to launch an enquiry into a rare form of cancer afflicting a small number of mine works. This condition resembles Mesothelioma. Mesothelioma arises from exposure to asbestos. The enquiry will determine whether the miners have contracted mesothelioma or a similar condition arising from exposure to taconite dust.