Tungsten processing, preparation of the ore for use in various products.

Tungsten exhibits a body-centred cubic (bcc) crystal lattice. It has the highest melting point of all metals, 3,410° C (6,170° F), and it has high conductivity for electricity. Owing to this unique combination of properties, it is used extensively as filaments for incandescent lamps, as electric contacts, and as electron emitters for electronic devices. Tungsten also has found wide application as an alloying element for tool steels and wear-resistant alloys. Tungsten carbides are used for cutting tools and hard-facing materials owing to their hardness and resistance to wear. The metal is brittle at room temperature but ductile and strong at elevated temperatures. Its alloys are employed in rocket-engine nozzles and other aerospace applications.

Tungsten Ores
Major minerals of tungsten are essentially of two categories. The first is wolframite [(Fe, Mn)WO4], which contains iron and manganese tungstates in all proportions between 20 and 80 percent of each. The second is scheelite (CaWO4), which fluoresces a bright bluish colour under ultraviolet light.

Tungsten deposits occur in association with metamorphic rocks and granitic igneous rocks. The most important mines are in the Nan Mountains in the Kiangsi, Hunan, and Kwangtung provinces of China, which possesses about 50 percent of the world’s reserves. In Russia, mines are located in the northern Caucasus and around Lake Baikal. There are also deposits in Kazakhstan. About 90 percent of South Korea’s tungsten is at Sang Dong. Canada’s Northwest Territories is home to the largest tungsten mine in the Western world, and a mine at Chojlla, Bol., is the largest producer in South America. Deposits in the United States are spread along the Rocky Mountains.

Extraction and refining - Ammonium paratungstate

Tungsten ores frequently occur in association with sulfides and arsenides, which can be removed by roasting in air for two to four hours at 800° C (1,450° F). In order to produce ammonium paratungstate (APT), an intermediate compound in production of the pure metal, ores may be decomposed by acid leaching or by the autoclave-soda process. In the latter process, the ground ore is maintained for 11/2 to 4 hours in a solution of 10–18 percent sodium carbonate at temperatures of 190° to 230° C (375° to 445° F) and under a pressure of 14.1–24.6 kilograms per square centimetre (200–350 pounds per square inch). Prior to the removal of unreacted gangue by filtration, the acidity is adjusted to pH 9–9.5, and aluminum and manganese sulfates are added at 70°–80° C (160°–175° F) and stirred for one hour. This can eliminate phosphorus and arsenic and reduce silica to a level of 0.03–0.06 percent. Molybdenum is removed by adding sodium sulfide at 80°–85° C (175°–185° F) at a pH of 10, holding for one hour, and then acidifying the solution to pH 2.5–3 and stirring for seven to nine hours to precipitate molybdenum sulfide. The remaining sodium tungstate solution can be further purified by a liquid ion-exchange process, using an organic extractant consisting of 7 percent alamine-336, 7 percent decanol, and 86 percent kerosene. During the countercurrent flow of the extractant through the solution, tungstate ions transfer from the aqueous phase to the organic phase. The tungsten is then stripped from the extractant into an ammonia solution containing ammonium tungstate. The resultant APT solution is sent to an evaporator for crystallization.

In the acid-leaching process, scheelite concentrate is decomposed by hydrochloric acid in the presence of sodium nitrate as an oxidizing agent. This charge is agitated by steam spraying and is maintained at 70° C (160° F) for 12 hours. The resultant slurry, containing tungsten in the form of a solid tungstic acid, is diluted and allowed to settle. The tungstic acid is then dissolved in aqueous ammonia at 60° C (140° F) for two hours under stirring. Calcium from the resulting solution is precipitated as calcium oxalate, while phosphorus and arsenic may be removed by the addition of magnesium oxide, which forms insoluble phosphates and arsenates of ammonium and magnesium. Iron, silica, and similar impurities that form colloidal hydroxides are removed by adding a small amount of activated carbon and digesting for one to two hours. The solution is clarified through pressure filters and evaporated to obtain APT crystals.

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Tungsten is found in the minerals Wolframite (iron-manganese tungstate, FeWO4/MnWO4), Scheelite (calcium tungstate, (CaWO4), ferberite and hübnerite. These are mined and used to produce about 37,400 tons of tungsten concentrates per year in 2000. China produced over 75% of this total, with most of the remaining production coming from Austria, Bolivia, Portugal, and Russia.

Tungsten is extracted from its ores in several stages. The ore is eventually converted to tungsten(VI) oxide (WO3), which is heated with hydrogen or carbon to produce powdered tungsten. It can be used in that state or pressed into solid bars.

Tungsten can also be extracted by hydrogen reduction of WF6 (WF6 + 3H2 → W + 6HF) or pyrolytic decomposition (WF6 + energy → W + 3F2).

Because it retains its hardness at high temperatures and has a high melting point, elemental tungsten is used in many high-temperature applications, such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles. Its high melting point also makes tungsten suitable for aerospace and high-temperature uses such as electrical, heating, and welding applications, notably in the gas tungsten arc welding process (also called TIG (tungsten/inert gas) welding).

Due to its conductive properties, as well as its relative chemical inertia, tungsten is also used in electrodes, and in the emitter tips in electron-beam instruments that use field emission guns, such as electron microscopes. In electronics, tungsten is used as an interconnect material in integrated circuits, between the silicon dioxide dielectric material and the transistors. It is used in metallic films, which replace the wiring used in conventional electronics with a coat of tungsten (or molybdenum) on silicon.

The electronic structure of tungsten makes it one of the main sources for X-ray targets, and also for shielding from high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive samples of FDG). Tungsten powder is used as a filler material in plastic composites, which are used as a nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.

The hardness and density of tungsten are applied in obtaining heavy metal alloys. A good example is high speed steel, which may contain as much as 18% tungsten. Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and coatings. Applications requiring its high density include heat sinks, weights, counterweights, ballast keels for yachts, tail ballast for commercial aircraft, and as ballast in race cars for NASCAR and Formula 1. It is an ideal material to use as a bucking bar for riveting, where the mass necessary for good results can be achieved in a compact bar. In armaments, tungsten, usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic energy penetrators as an alternative to depleted uranium but may also be used in cannon shells, grenades and missiles to create supersonic shrapnel. High-density alloys of tungsten may be used in darts (to allow for a smaller diameter and thus tighter groupings) or for fishing lures (tungsten beads allow the fly to sink rapidly). Some types of strings for musical instruments are wound with tungsten wires. Its density, similar to that of gold, allows tungsten to be used in jewelry as an alternative to gold or platinum. Its hardness makes it ideal for rings that will resist scratching, are hypoallergenic, and will not need polishing, which is especially useful in designs with a brushed finish.

Tungsten compounds are used in catalysts, inorganic pigments (e.g. tungsten oxides), and as high-temperature lubricants (tungsten disulfide). Tungsten carbide (WC) is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking, woodworking, mining, petroleum and construction industries and accounts for about 60% of current tungsten consumption. Tungsten oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. Crystal tungstates are used as scintillation detectors in nuclear physics and nuclear medicine. Other salts that contain tungsten are used in the chemical and tanning industries.

Lately, tungsten is used for jewelry because of its longevity and high durability.

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There are several types of light that could be referred to as 'halogen', most commonly are tungsten halogen which are very similar to normal lights and metal halide which are discharge lamps.

Tungsten halogen bulbs are able to run hotter and therefore brighter than 'plain' tungsten bulbs so for a given amount of light the T/H bulb can use a bit less power. T/H tend to be used where the colour temperature (whiteness as opposed to yellowness) is important for good colour display.

Metal halide lamps are often used in shops giving a very efficient but slightly purple tinged colour, the require completely new (and quite expensive luminaires)

Low voltage lamps tend to be more efficient than mains as the filament is shorter and more compact but there is additional cost in the transformer/power supply required.
The most efficient lights are LED 'bulbs' but again they require a dedicated type of power supply or more expensive versions of the bulb.

LEDs have the advantage of a very long lifetime, so reducing maintenance costs.

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Tungsten ore low, must be integrated mineral-rich concentrate to a smelting raw material. According to the type of tungsten ore dressing into wolframite and scheelite mineral beneficiation two types. Present mining to wolframite quartz vein type, accounting for the amount of ore taken out more than 90%. Tungsten ore dressing methods mainly hand-selected, HM election, re-election, flotation, magnetic separation and electrostatic separation methods such as. Wolframite in order to re-election dominated by flotation mainly scheelite. Most of our wolframite is easy to choose the type of ore, while the composition of scheelite ore complex, and mostly of refractory ore, coupled with low grade, so not a lot of development.

In addition, tungsten oxide minerals such as tungsten China currently not recycled. China's tungsten ore dressing and processing plant started in 1952 a large-scale factory in Dajishan Tungsten establish 125t / d of gravity concentration plant, the late 50s, former Soviet Union Mechanobr Research and Design Institute for the down hill , West Mountain and hilly Miyama tungsten designed three large-scale tungsten ore processing plant put into operation one after another. 40 years in the production practice constantly sum up experience, and absorb foreign advanced technology dressing, through continuous improvement, so that beneficiation process is improving daily, processing technical and economic indicators have reached the world advanced level.

Nanchang representative non-ferrous metals such as tungsten ore beneficiation company targets, despite nearly 10 years in the annual decline in ore grade, the tungsten recovery remained at 84% or more of the high concentrate grade (WO3) 66.7 % ~ 68.9% (up to 12 tungsten national standards: WO3 content is not less than 65%), ore grade (WO3) 0.25% ~ 0.27%, tailing grade (WO3) 0.036% ~ 0.046%. Tungsten smelting and fire refining method and two kinds of water law. The use of wolframite concentrate or smelting scheelite concentrate, but different smelting process, so both wolframite deposit, there scheelite, we must each ore body, each calculated reserves. When the ore wolframite, scheelite coexist together, to elect a black tungsten concentrate and scheelite concentrate for smelting, respectively. The smelting of mineral raw materials as tungsten tungsten ore concentrates, containing WO3 should meet or greater than 65%.

The pyrometallurgical into tungsten alloy (with W>70 or>65%) by Water Act, a positive tungsten smelting sodium, calcium APT or tungsten, etc.. Finally, further processed into tungsten trioxide (containing WO3>=99.9%), then reducing agent (usually hydrogen) is reduced to tungsten powder (with W>=99.9%) and so on.

Tungsten is recovered from scheelite ore concentrates, or other tungsten concentrates which may, or may not contain scheelite in the form of sodium tungstate and in yields up to 99.5 percent or more by a process in which ground ore substantially below 200 mesh in particle size is first added to a 50 percent sodium hydroxide solution while being agitated to such an extent that the resulting mixture becomes a semi-solid as the temperature is raised above 80°C. The semi-solid is then baked at 135 to 145°C for about 1 to 2 hours, followed by adding sufficient water to the semi-solid to form a slurry having a sodium hydroxide concentration below 6 molar, separating the causticinsoluble sludge from the slurry and washing the sludge with a dilute sodium hydroxide solution to remove residual sodium tungstate.

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