The process of mining low-grade iron ore, or taconite, requires massive resources. Heavy industrial mining equipment, expansive mines, and a skilled labor pool are all required. Some of the equipment includes diamond-bit rotary drills, hydraulic shovels and loaders, water-wagons, production trucks and heavy duty conveyors.
Creating steel from low-grade iron ore requires a long process of mining, crushing, separating, concentrating, mixing, pelletizing, and shipping. Once the taconite pellets are formed, they are shipped to the customers and various steel mills.
Short Tour & Mining Process Overview
Mining, blasting, crushing, concentrating, agglomerating are some of the terms associated with mining process. Let’s talk about them as well as machinery, and processes that aren’t the elements of everyday conversation to folks outside of the mining industry.
First, a low-grade iron ore called taconite is mined. This taconite rock is about 28 percent iron, the rest sand or silica for the most part. The purpose of this process is to take this low-grade taconite rock and process it to remove most of the sand/silica and prepare it for shipment to a steel plant to make it into finished steel.
Once the low-grade ore is mined, it is then crushed, and grinded to as fine as face powder. After grinding this fine ore is mixed with water and a series of magnets are run over it. The magnets grab the iron particles and the rest is discarded. For every ton of retained iron about two tons of tailings are discarded / wasted.
Once the iron is captured in a “concentrated” form, the water is removed, a little clay added to serve as a binder, and finally the material is rolled into a small pellet about the size of a marble. These iron ore pellets are heated in a large, natural gas fired kiln to 2400 degrees F to harden them for shipment. The pellets are cooled and screened for quality and then loaded onto trains and ore boats for shipment to blast furnaces and steel mills. That’s where these iron ore pellets are turned into finished steel for shipment to auto and appliance manufacturers, steel building producers, and others.
The iron ore concentrate, mixed with Bentonite, is formed into soft pellets in balling drums in the pellet plant – it is done in much the same manner that one would roll a snowball. The goal is to make a pellet about the size of a marble (between 1/4″ and 1/2″). Pellets are screened to meet the size specification, with undersized or oversized crushed and returned to the balling drums.
The soft pellets are then delivered to the roller feeder for final removal of the fines, which are also returned to the balling circuits. The correctly sized soft pellets are delivered to the traveling grate furnace for further drying and preheating. The grate is fired by natural gas.
From this point, the pellets are charged into the large rotary kiln where they are heat-hardened at 2,400 degrees Fahrenheit. The pellets are discharged into the revolving cooler and then moved to the pellet screening plant on to the pellet loadout system.
The whole process consumes a lot of energy in the form of electricity and natural gas. Millions of dollars, over the last several years, have been spent to improve energy efficiency and to recoup waste heat and re-use it in the process. These efforts have significantly reduced expenditures on energy.
Watch this short Discovery Channel Video that shows iron ore to steel transformation process.