Smelting plants extract metal from ore through heating and a reducing agent. Early examples include the bloomery and blast furnace for iron smelting. The Bessemer process and basic oxygen steelmaking improved efficiency. Aluminum smelting plants use electrolysis.
A smelting plant is an industrial location where metal for ore is mined. Common examples of metal smelting include tin, lead, copper, bronze and iron. The mining of pure aluminum is also called smelting, although the process is significantly different from that of other minerals.
Metals begin their working life as ore. A mineral is generally defined as a rock, or group of minerals, that has potential economic value. The ore doesn’t just contain the metal of interest. For example, iron ore is a rock that contains iron bound to other chemical compounds and minerals. Ore smelting is the process of removing the metal of interest from its original rock.
Smelting, as the sound perhaps suggests, involves the partial smelting of the ore. The ore must be heated in an oxidizing environment until the chemicals begin to mobilize or become available. Some impurities can be removed by heat and if the metal of interest is in the form of a sulfide, the heat and the presence of oxygen may be sufficient to convert it to an oxide. However, it is not possible to simply smelt metal from ore.
In addition to heat, smelting also requires a reducing agent. The metal of interest probably exists as an oxide or will be converted to an oxide during initial heating. A sufficiently strong reducing agent will be able to convert the oxide into pure metal and some waste product.
An early example of a smelting plant was a bloomery, used by a blacksmith to smelt iron ore. Inside a bloomery, iron ore is heated in the presence of coal, or pure carbon fuel, and moving air. When the ore is heated, the carbon monoxide from the coal reduces the iron oxide.
The smelting reaction inside a bloomery produces a relatively pure iron metal and carbon dioxide as a waste product. As the bellows blows through the bloomery, carbon dioxide is evacuated, allowing the reaction to continue. The metal and impurities, called slag, fall to the bottom of the furnace as the iron ore is reduced. Typically, the iron is heated a second time to hammer the slag out of the now wrought iron.
Another early form of iron smelting is the blast furnace, which has a particularly ancient history in China. In the mid-1800s, however, iron ore was smelted into steel, which is a much purer form of iron metal. This industrial transition to steelmaking was made possible by the development of the Bessemer process, in which air blown through molten iron is able to remove most impurities. Beginning in 1950, the dominant mining method found at any given iron smelting plant became basic oxygen steelmaking (BOS). BOS improves the basic Bessemer process by blowing pure oxygen through the molten iron, which dramatically improves smelting plant efficiency.
Many other metals undergo smelting as a method of extraction, and many of the techniques of the various smelting plants and smelting equipment follow the same basic principles. Also, aluminum mining is also called smelting. Aluminum smelting plants differ in that they carry out an electrolytic process. Electric current is passed through the liquid molten cryolite, in which the aluminum oxide has been dissolved. The corresponding oxidation and reduction that occurs at the electrical anode and cathode converts the aluminum oxide into pure aluminum.
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