Description
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Tungsten is a transition metal that has a shiny grey white color in its natural solid state. It is soft enough to be cut with a hacksaw in its pure form, but it is a brittle metal. Tungsten has an atomic weight of 183.84, a melting point of 6192 °F, and a boiling point of 10031 °F. Some common uses of tungsten include: as a component in cemented carbides, as a filament in light bulbs, alloyed with other metals to create heavy metal alloys, and as a component in turbine blades.
Isolation
Tungsten occurs most often in nature with minerals such as wolframite and scheelite. The isolation procedure is lengthy as tungsten does not occur in its free state in nature.
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There are a few different ways that tungsten can be concentrated and isolated. The first step takes mixed ore residues and low grade tungsten ore and subjects the ore to roasting and leaching using soda. This solution is purified using the calcium oxide of wolframite which results in the decomposition of tungsten to tungstic acid. The acid is dissolved in an ammonia solution and crystallization of the tungsten results in ammonium paratungstate. Hydrogen and carbon applications further isolate the tungsten.
Isolation of high grade tungsten ore also begins with treating the ore with soda or a caustic autoclave leach. Further purification is performed along with a liquid or solid ion exchange. The products that result from crystallization are ammonium paratungstate which are further reduced using hydrogen and carbon applications. Tungsten can also be recycled and isolated again from tungsten scrap metals; in this process the scrap is oxidized and chemically processed again to ammonium paratungstate.