Added: Laryn Grimmett - Date: 19.01.2022 01:20 - Views: 12673 - Clicks: 1249
Iron ores occur in igneous, metamorphic transformedor sedimentary rocks in a variety of geologic environments. Most are sedimentary, but many have been changed by weathering, and so their precise origin is difficult to determine. Hematite and magnetite are by far the most common types of ore. Pure magnetite contains Deposits with less than 30 percent iron are commercially unattractive, and, although some ores contain as much as 66 percent iron, there are many in the 50—60 percent range.
Silica SiO 2 and phosphorus-bearing compounds usually reported as P 2 O 5 are especially important because they affect the composition of the metal and pose extra problems in steelmaking. ChinaBrazil, Australia, Russia, and Ukraine are the five biggest producers of iron ore, but ificant amounts are also mined in India, the United StatesCanada, and Kazakhstan. Japan, the European Unionand the United States are the major importers. Most iron ores are extracted by surface mining.
Some underground mines do exist, but, wherever possible, surface mining is preferred because it Find Iron belt cheaper. As-mined iron ore contains lumps of varying size, the biggest being more than 1 metre 40 inches across and the smallest about 1 millimetre 0.
The blast furnacehowever, requires lumps between 7 and 25 millimetres, so the ore must be crushed to reduce the maximum particle size. Crushed ore is divided into various fractions by passing it over sieves through which undersized material falls.
In this way, lump Find Iron belt rubble ore 7 to 25 millimetres in size is separated from the fines less than 7 millimetres. If the lump ore is of the appropriate quality, it can be charged to the blast furnace without any further processing. Fines, however, must first be agglomerated, which means reforming them into lumps of suitable size by a process called sintering. Iron ore sintering consists of heating a layer of fines until partial melting occurs and individual ore particles fuse together.
For this purpose, a traveling-grate machine is used, and the burning of fine coke known as coke breeze within the ore generates the necessary heat. Before being delivered to the sinter machine, the ore mixture is moistened to cause fine particles to stick to larger ones, and then the appropriate amount of coke is added. Initially, coke on the upper surface of the bed is ignited when the mixture passes under burners in an ignition hood, but thereafter its combustion is maintained by air drawn through the bed of materials by a suction fan, so that by the time the sinter reaches the end of the machine it has completely fused.
The grate on which the sinter mix rests consists of a series of cast-iron bars with narrow spaces between them to allow the air through. After cooling, the sinter is broken up and screened to yield blast-furnace feed and an undersize fraction that is recycled.
Modern sinter plants are capable of producing up to 25, tons per day. Sintering machines are usually measured by hearth area; the biggest machines are 5 metres 16 feet wide by metres long, and the effective hearth area is square metres 6, square feet.
Concentration refers to the methods of producing ore fractions richer in iron and lower in silica than the original material. Most processes rely on density differences to separate light minerals from heavier ones, so the ore is crushed and ground to release the ore minerals from the gangue. Magnetic techniques also are used. The upgraded ore, or concentrate, is in the form of a very fine powder that is physically unsuitable for blast furnace use.
It has a much smaller particle size than ore fines and cannot be agglomerated by sintering. Instead, concentrates must be agglomerated by pelletizing, a process that originated in Sweden and Germany about —13 but was adapted in the s to deal with low-grade taconite ores found in the Mesabi Range of Minnesota, U. First, moistened concentrates are fed to a rotating drum or an inclined disc, the tumbling action of which produces soft, spherical agglomerates.
Finally, they are slowly cooled. Finished pellets are round and have diameters of 10 to 15 millimetres, making them almost the ideal shape for the blast furnace. The earliest kind of firing equipment was the shaft furnace. This was followed by the grate-kiln and the traveling grate, which together for more than 90 percent of world pellet output.
In shaft furnaces the charge moves down by gravity and is heated by a counterflow of hot combustion gases, but the grate- kiln system combines a horizontal traveling grate with a rotating kiln and a cooler so that drying, firing, and cooling are performed separately. In the traveling-grate process, pellets are charged at one end and dried, preheated, fired, and cooled as they are carried through successive sections of the equipment before exiting at the other end.
Traveling grates and grate-kilns have similar capacities, and up to five million tons of pellets can be made in one unit annually. Videos Images. Additional Info. Load .
Ores Iron ores occur in igneous, metamorphic transformedor sedimentary rocks in a variety of geologic environments. Mining and concentrating Most iron ores are extracted by surface mining. Lumps and fines Crushing As-mined iron ore contains lumps of varying size, the biggest being more than 1 metre 40 inches across and the smallest about 1 millimetre 0.
Sintering Iron ore sintering consists of heating a layer of fines until partial melting occurs and individual ore particles fuse together. Pelletizing First, moistened concentrates are fed to a rotating drum or an inclined disc, the tumbling action of which produces soft, spherical agglomerates.
People Are Talking About. Load Next .Find Iron belt
email: [email protected] - phone:(881) 932-2137 x 3452
Dyson Sphere Program guide: how to get set up in under an hour