Iron Ore Beneficiation
Iron ore occurs naturally in a variety of forms, from sand-like iron fines to solid rock masses. Crude ore, or ore mined in the natural state, seldom occurs in a pure state and requires some form of beneficiation. Crude ore is commonly mixed with other minerals (gangue), which reduce the iron content. Concentrations of as little as 30 percent may be of commercial interest, provided other factors such as gangue content, the size of the deposit, and accessibility are favorable. Crude iron ore is classified in three general categories:
• Direct Shipping - Direct shipping ores are transported as mined or possibly after screening. Direct shipping ores are generally hematite, magnetite, or goethite. Reserves of these ores are rarely found in North America because they have been mostly depleted. There are many grades of direct shipping ores, including lump ores usually crushed to 20 - 30 mm and sinter fines with a maximum grain size of 6 - 10 mm. The prices of direct shipping ores are often related to the historical Mesabi standard of 51.5 percent iron.
• Concentrates - Iron ore that requires beneficiation to upgrade the iron content is called low-grade, intermediate, taconite, or concentrating ore. “Concentrating” or otherwise treating iron ore to remove impurities and improve its quality is referred to as beneficiating.
• Agglomerated - The development of techniques of mining and concentrating taconite led to the introduction of the iron-ore pellet. Pellets are comprised of ore that has been agglomerated into balls. The pellet is the major form of introducing iron into the steelmaking blast furnace. The effect of pelletizing taconite iron has been to encourage mines throughout the world to grind, concentrate and pelletize otherwise low-grade ores. Another form of agglomeration commonly used is briquetting.
Iron ores often contain impurities, undesirable chemical components such as phosphorous, sulfur, sodium, potassium (alkalis), alumina, silica and sometimes titanium. Other components such as calcium and manganese, may be considered desirable, depending on the composition of other raw materials used in the individual iron or steel producer's process.
There are a variety of beneficiation methods that can be used to prepare iron ores, depending on the iron content in the ores. Some ores contain greater than 60 percent iron and require only crushing and blending to prepare them for further beneficiation. In other cases, operations including screening and concentrating are necessary to prepare the raw materials. Generally, the operations required before the iron ore is considered a finished product include:
• Crushing & Screening
• Grinding
• Concentration
• Agglomeration
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