|Tungsten, (or Wolfram as it is known in many parts of the world) is an extremely hard and very dense gray to white metallic element extracted from wolframite, scheelite and other minerals. Tungsten has the highest melting point, lowest coefficient of expansion and lowest vapor pressure of any metal. It is also corrosion resistant and does not break down or decompose. Due to its unique attributes tungsten has few, if any, replacements in a majority of its industrial applications.
- Second only to diamond (tungsten carbide)
- Industrial applications - high speed cutting tools, heavy machinery, specialty alloys
- Highest melting point and lowest coefficient of expansion of all metals
- Industrial applications - jet turbine engines, light bulb filaments
- Greater than lead and uranium
- Industrial applications - sporting goods (golf clubs, tennis racquets, darts), ballast
- Does not break down or decompose
- Industrial applications - sports fishing weights, shotgun shot, new applications being developed as an alternative to lead
Minerals and Deposits
Tungsten occurs in nature only in the form of chemical compounds. Although more than thirty tungsten bearing minerals are known, only two of them are important for industrial use, namely wolframite and scheelite.
Pure scheelite has blue-white fluorescence in ultraviolet light, a property which is utilised in prospecting. Wolframite is a general term for iron and manganese tungstates where the iron/manganese ratio can vary. A mineral with more than 80% FeWO4 is called Ferberite and a mineral with more than 80% MnWO4 is called Hübnerite.
All tungsten deposits are of magmatic or hydrothermal origin. During cooling of the magma, differential crystallization occurs, and scheelite and wolframite are often found in veins where the magma has penetrated cracks in the earth's crust. Most of the tungsten deposits are in younger mountain belts, i.e. the Alps, the Himalayas and the circum-Pacific belt.
The concentration of workable ores is usually between 0.3% and 1.0% WO3
Source: USGS, 2007
Ammonium Paratungstate (APT)
APT [(NH4)10[H2W12O42] · 4 H2O] is the main intermediate and also the main tungsten raw material traded in the market. APT is usually calcined to yellow (WO3) or blue oxide (WO3-X; a slightly substoichimetric trioxide with varying oxygen content).
Tungsten Metal Powder (W)
Yellow or blue oxide is reduced to tungsten metal powder by hydrogen. The reduction is carried out either in pusher furnaces, in which the powder passes through the furnace in boats, or in rotary furnaces, at 700-1,000°C.
Tungsten Carbide (WC)
Most of the tungsten metal powder is converted to tungsten carbide (WC) by reaction with pure carbon powder, e.g. carbon black, at 900 - 2,200°C in pusher or batch furnaces, a process called carburization.
Tungsten carbide is, quantitatively, the most important tungsten compound. Because of its hardness, it is the main constituent in cemented carbide (hardmetal).
Tungsten Conversion Measurements
NOTE: If the price of WO3 is US$265/MTU = US$26.50/kg = US$12.02/lbs
|W (Elemental Tungsten) : 1
||WO3 (Tungsten Concentrate) : 1.2616
|1 short ton||2,000 lbs|
|1 metric tonne||2,204.6 lbs |
|1 STU (Short Ton Unit)||= 20 lbs (1% of a short ton)|
|1.1023 STU||1 MTU (Metric Ton Unit)|
|1 MTU||10 kgs (1% of a metric tonne) |
|1 MTU||22.04 lbs|
|1 Ton (2,000)||0.907 Tonnes|
|1 Tonne||100 MTU |