|MadSci Network: Earth Sciences|
Typically, hematite is mined by open pit mining. Overburden is removed, then the ore is mined from an ever-deepening hole. The mineral and rock is first stripped by blasting the rock with explosives and removing it with enormous trucks - with capacities over 150 tons. The ratio of mineral to rock can be quite large - up to 1.5 to 1 for hematite. The material is stored in a covered building after being reduced to no greater than 10 inches in diameter in a primary crusher. The material is about 35% iron and is processed into pellets. The next step in the process is Grinding. Using large mills, material can be ground to the consistency of beach sand or powder, without the addition of steel balls as is often used in other milling operations. The waste rock and water is removed and becomes the mines "tailings". Seperating hematite involves adding Caustic soda and cooked corn starch during and after grinding, along with water to collect all the fine- grained ore together in flotation cells, called deslime thickeners. The thicker ore-starch-soda material sinks and the water and waste rock float off the top and are removed as tailings. At this point the material is dewatered and mixed with the proper amount of limestone and dolomite according to customer requirements. Steam is added to the hematite process as it is harder to dewater. In the pelletizing process the ore is rolled with bentonite clay (a binder) to marble size pellets in balling drums. The produce at this time is called "green balls" and is then conveyed to a rotary kiln fired at 2200 degrees Fahrenheit. The kilns can burn natural gas, coal or oil as a fuel. The pellets are cooled and transported to the stockpile. A loading yard loads ore into special rail. The tailings are conveyed to a basin where the water is recycled and reused and the tailings remain in the impoundment. see the following site for photos and a cybertour of a working mine http://www.mining-technology.com/projects/snim/ http://www.copperrange.org/lsi2.htm
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