MadSci Network: Earth Sciences

Re: How is Hematite mined?

Date: Tue Jan 20 07:45:05 2004
Posted By: Dave Clark, Staff, Chemical and Environmental Technologies, Battelle
Area of science: Earth Sciences
ID: 1074192424.Es

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 
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 

see the following site for photos and a cybertour of a working mine

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