Iron ore and its beneficiation:

Iron ore and its beneficiation:

Most useful metal in the world, Iron, is extracted from iron ore. It is the rock from which metallic iron can be economically extracted. Iron ore is a mineral substance which, when heated in the presence of a reductant, will yield metallic iron (Fe). The iron ore, usually, very rich in iron oxides (Fe3O4 and Fe2O3). Iron ores are mostly dark grey to rusty red in color and high specific gravity. Two main types of iron ore used for iron making – Magnetite (Fe3O4) and Hematite (Fe2O3). Common iron ores include:

• Hematite - Fe₂O₃ - 70 percent iron
• Magnetite - Fe₃O₄ - 72 percent iron
• Limonite - Fe₂O₃ + H₂O - 50 percent to 66 percent iron
• Siderite - FeCO₃ - 48 percent iron

Iron ore is the source of primary iron for the world's iron and steel industries. It is therefore essential for the production of steel, which in turn is essential to maintain a strong industrial base. Almost all (98%) iron ore is used in steelmaking. Iron ore is mined in about 50 countries. The seven largest of these producing countries account for about three-quarters of total world production. Australia and Brazil together dominate the world's iron ore exports, each having about one-third of total exports.

Hematite deposits are mostly sedimentary in origin, such as the banded iron formations (BIFs). BIFs consist of alternating layers of chert (a variety of the mineral quartz), hematite and magnetite. They are found throughout the world and are the most important iron ore in the world today. Their formation is not fully understood, though it is known that they formed by the chemical precipitation of iron from shallow seas about 1.8-1.6 billion years ago, during the Proterozoic period.

Magnetite also mostly found in Banded iron formations (BIF). They are fine grained metamorphosed sedimentary rocks composed predominantly of magnetite and silica. Mining and processing of BIF formations involves coarse crushing and screening. Magnetite is beneficiated by crushing and then separating the magnetite from the gangue minerals with a magnet. This is usually so efficient that lower grade ore can be treated when it is magnetite than a comparable grade of hematite ore, especially when the magnetite is quite coarse.

Magnetic separation and flotation are the most widely accepted technologies for the upgrading of iron ore particles, but these processes result in iron concentrate with high amounts of very fine and/or interlocked silica particles.

Inferior sources of iron ore generally required beneficiation. Due to the high density of hematite relative to silicates, beneficiation usually involves a combination of crushing and milling as well as heavy liquid separation. This is achieved by passing the finely crushed ore over a bath of solution containing bentonite or other agent which increases the density of the solution. When the density of the solution is properly calibrated, the hematite will sink and the silicate mineral fragments will float and can be removed.