Tungsten is produced in a variety of minerals, including wolframite, scheelite, and ferberite. It is the second most abundant metal after carbon, and it is used in a variety of industrial applications, such as munitions, medical implants and powertrain components for automobiles.
Tungsten ores usually contain sulfide and arsenic minerals in addition to tungsten trioxide (WO3). These impurities are removed by roasting or leaching.
Acid leaching is a common process for acidizing scheelite and other tungsten ores. In this process, scheelite is decomposed by the action of hydrochloric acid under the addition of sodium nitrate as an oxidizing agent.
During the acid leaching of scheelite, the tungsten is formed in a solid form called tungstic acid. Aqueous ammonia solution can be used to dissolve tungstic acid and remove phosphates and calcium from the slurry.
The resulting solution is then evaporated to dryness in air and the remaining tungstic acid is concentrated by acid leaching and further purified by a liquid ion exchange process using an organic extractant. The resulting ammonium paratungstate (APT) is heated with hydrogen to produce tungsten oxide or reacts with carbon to form tungsten metal.
Tungsten is also found in some ores as the metal tungstate and can be further separated from other tungsten elements by heat treatment at temperatures above 1925degF (1050degC). It can be used in a variety of industrial applications, including munitions, medical implants and powertrain component.
Tungsten is the highest tensile strength of any known metal. It is also the most ductile of all alloys. It is commonly used in the manufacture of high-speed steel and tool steel. It is also used in the production of various munitions, such as bullets and bombs. It is a very durable alloy and has a high melting point.
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