Tungsten ores

Tungsten does not occur naturally in its pure metallic state; rather, it is found in several ores, but only two kinds of tungsten-bearing mineral rocks, called wolframite and scheelite, are mined commercially. Wolframite accounts for about 70% of the total tungsten resources in the world, and scheelite accounts for about 30%.

Wolframite

Wolframite is not scientifically classified as an individual mineral species by the International Mineralogical Association (IMA). However, it is widely recognized as a mineral series, with the minerals huebnerite and ferberite being its end members. Huebnerite is the manganese rich end member while ferberite is the iron rich end member. Wolframite is a reddish-brown to grayish-black lustrous mineral which is the chief ore of the metal tungsten.

Wolframite mainly occurs in quartz veins and pegmatites associated with granitic intrusive rock. Notable occurrences include the Nanling Range, China; southwestern states and Colorado in the USA; Russia; Korea; England; Bolivia; Portugal; Australia; Myanmar and the Malay Peninsula. Wolframite ore can be concentrated by gravity (spirals, cones, tables), sometimes in combination with magnetic separation.

Because Wolframite is a strong and quite dense material with a high melting temperature, it is an ideal material for electric filaments and armor-piercing ammunition, as well as hard tungsten carbide machine tools.


 

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Wolfram is kind of essential mineral to get tungsten, and it is usually inlayed in granite and quartz together with cassiterite. Wolfram is weak magnetic with its density of 7.2-7.5g/cm³ and mohs hardness of 4-4.5.

The process of wolfram dressing is mainly gravity separation while sometime intensity magnetic separation can be involved. Wolfram tungsten ore is usually inlayed with coarse granules with big density and small hardness, so the specific separation or concentration of wolframite tungsten can be pre-selection, gravity separation after screening & classifying, intensity magnetic separation and treatment of fine tungsten mud.

The big density difference between wolfram and gangue makes gravity separation workable if the wolframite tungsten granules can be liberated or dissociated from the impurities. For the coarse tungsten or blocky tungsten separation, gravity separation can be used to get the coarse wolframite granules. Here the main wolfram dressing plant is jigging machine. The wolfram ore concentration machine can deal with ore of +80 meshes to 30mm. For some finer tungsten ore, shaking table or other equipment can be used to get the fine wolframite grains.

In the gravity separation of wolramite tungsten, the common processing plant can be jig separator and shaking table. Jigging machine is especially important to beneficiate wolfram tungsten of coarse and medium granules. The raw wolframite tungsten needs crushing and screening before jigging processing to gain high grade tungsten.

As kind of wolfram beneficiation machine, jig has been added to the circle of milling in order to reduce the pelitization of tungsten. The tungsten concentrate from jigging gravity concentration occupies a big part of the whole concentrate.

Shaking table is to separate wolfram of fine grains with its good enrichment ratio, great beneficiation efficiency. So the classifying of raw wolfram ore is necessary before separation.



 

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Tungsten collimators are used in linear accelerators used for radiotherapy treatments. Tungsten collimators help to shape the beam of radiation emerging from the machine, they can limit the maximum field size of a beam. The treatment head of a linear accelerator consists of both a primary and secondary collimator. The primary collimator is positioned after the electron beam has reached a vertical orientation. When using photons, it is placed after the beam has passed through the X-ray tungsten target. The secondary collimator is positioned after either a flattening filter (for photon therapy) or a scattering foil (for electron therapy). The secondary collimator consists of two jaws which can be moved to either enlarge or minimize the size of the treatment field.

New systems involving multileaf collimators (MLCs) are used to further shape a beam to localize treatment fields in radiotherapy. MLCs consist of approximately 50–120 leaves of heavy, metal tungsten collimator plates which slide into place to form the desired field shape.

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For industrial radiography using gamma radiation sources such as Iridium-192 or Cobalt-60, a collimator allows the radiographer to control the exposure of radiation to expose a film and create a radiographic "negative", a.k.a., a radiograph, to inspect materials for defects. A collimator in this instance is most commonly made of tungsten, and is rated according to how many half value layers tungsten material contains, i.e., how many times tungsten material reduces undesirable radiation by half. For instance, the thinnest walls on the sides of a 4 HVL tungsten collimator 0.52" thick will reduce the intensity of radiation passing through them by 88.5%. The shape of these collimators allows the radiographer to direct the radiation to the film and away from other workers.

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The main component of tungsten ore is tungsten.Tungsten is a dull silver-colored metal with the highest melting point of any pure metal.Also known as wolfram, from which the element takes its symbol, W, tungsten is more resistant to fracturing than diamond and is much harder than steel. It is the refractory metal's unique properties - its strength and ability to withstand high temperatures - that make it ideal for many commercial and industrial applications.

Applications:

Tungsten's primary application for over 100 years has been as the filament in incandescent light bulbs. Doped with small amounts of potassium-aluminum silicate, tungsten powder is sintered at high temperature to produce the wire filament that is in the center of light bulbs that light millions of homes around the world.

Due to tungsten's ability to keep its shape at high temperatures, tungsten filaments are now also used in a variety of household applications, including lamps, floodlights, heating elements in electrical furnaces, microwave ovens, x-ray tubes and cathode-ray tubes (CRTs) in computer monitors and television sets. The metal's tolerance to intense heat also makes it ideal for thermocouples and electrical contacts in electric arc furnaces and welding equipment. Applications that require a concentrated mass, or weight, such as counterweights, fishing sinkers and darts often use tungsten because of its density.




 

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The main component of tungsten ore is tungsten.Tungsten is a dull silver-colored metal with the highest melting point of any pure metal.Also known as wolfram, from which the element takes its symbol, W, tungsten is more resistant to fracturing than diamond and is much harder than steel. It is the refractory metal's unique properties - its strength and ability to withstand high temperatures - that make it ideal for many commercial and industrial applications.

Production:

Tungsten is primarily extracted from two types of minerals, wolframite and scheelite. However, tungsten recycling also accounts for about 30% of the global supply. China is the world's largest producer of the metal, providing over 80% of the world supply.

Once tungsten ore has been processed and separated, the chemical form, ammonium paratungstate (APT), is produced. APT can be heated with hydrogen to form tungsten oxide or will react with carbon at temperatures above 1925°F (1050°C) to produce tungsten metal.




 

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As kind of common metal, tungsten is usually mixed in kinds of rocks with its low content, and it can be smelted after beneficiation. There is wolframites and Scheelite and at this moment, wolframites has been in dominating place to explore, occupying over 90%. For tungsten enrichment, hand separation, heavy medium separation, gravity separation, floatation separation, magnetic separation and electrical separation has been involved.

For wolframite tungsten ore, it has characteristics of low content, low grade, coarse granule inlay, big density, low hardness, easy argillization, and dark color. Its beneficiation is mainly gravity separation. The density difference between wolframites and impurities is big and gravity separation can be adopted. But the wolframites granules shall be liberated from the impurities. So the promary situation is to observe the crystal granule size of wolframites. If the wolframites inlay is corse or it is lumpy wolframites, coarse mineral jig separator can be used directly to gain high grade tungsten ore. The equipment involved cover crusher, rod mill, jig concentrator. If it is fine granules inlay or wolframites mud, shaking table or centrifugal separator can be used.

But for scheelite tungsten ore, it is usually mixed with sulfide, mainly molybdenite, and the beneficiation for scheelite is floatation separation. In alkaline medium, The PH is 9-10.5 by sodium carbonate and sodium hydroxide. The main inhibitor is sodium silicate, quebracho sap, tannin, and kinds phosphate while the main collectors are oleic acid, sodium oleate, tall oil, paraffin soap oxide. These collectors owns foaming nature, so there is no need of foaming agent here. In order to improve the floatation efficiency of scheelite ore, polyvalent metalsalts can be added to the solium silicate while pulp temprature shall be up to 70-90 celsius degree.



 

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There are 10 types of tungsten ore deposits in South China. Four types of fluid inclusions were found:

I.iquid-rich; II.Gas-rich; III.Liquid CO^2-bearing; IV.Polyphase with daughter minerals.

Most common are type I inclusions. Type IV fluid inclusions only appeared in the porphyry and skarns. In skarns, type IV inclusions are evidently confined to the early stage, i.e., the simple silicate stage, but in the later scheelite mineralization stage, only types I and III inclusions occurred. Types II and III were found in the wolframite-quartz-sulfide veins, especially at the top of the veins.

Homogenization temperature and salinity were determined on the inclusions, and the pressure of formation was estimated from the inclusions. The homogenization temperatures of some of these types of tungsten ore deposits are as follows: porphyry, 386°C; greisen, 244–301°C; granite, 220°C; wolframite-sulfide-quartz veins, 240–310°C; wolframite-microcline-quartz veins, 267–325°C; stratabound, 219°C; and ferberite-quartz veins. 142°C. The salinity of fluid inclusions in the wolframite-sulfide-quartz veins type was only 5–10% equiv. NaCl. The pressures of formation, determined from the tomperature of homogenization, volume and density of phases in H₂O-CO₂ inclusions, from veins in three different wolframite-sulfide-quartz deposits, were 450, 550, and 750 atm., respectively. Most of the tungsten ore deposits were formed between 220°C and 390°C, with the porphyry highest and the ferberite-quartz veins type lowest. In the wolframite sulfide-quartz veins, four stages can be recognized: oxide-silicate; wolframitequartz-beryl; wolframite-quartz-sulfide; and carbonate. Throughout this sequence, the salinity and temperature decrease, e. g., from 293°C to 129°C.

It is concluded that these particular tungsten deposits were formed from a dilute water solution at moderate to high temperatures and at moderate pressures.

 

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There are 10 types of tungsten ore deposits in South China: granite, porphyry, volcanic, pegmatite, skarn, greisen, wolframite-quartz ± microcline veins, stratabound, ferberite-quartz veins and placer. Most are chronologically related to Yenshanian granites. Integrated field, mineralogic, fluid inclusion and geochemical studies were undertaken to determine the characteristics and origin of the ores.

Most of the tungsten ore deposits are also spatially related to Yenshanian granites. These granites include several intrusions, isotopically dated at 160–180 m. y. and 70–100 m. y. The concentration of trace elements, especially W Mo, Sn, Ta, Nb, Li, and F are relatively high in the granites. In the granites of South China, the average WO₃ is 4.35 ppm, but in Yenshanian granites, which are the youngest of these, the average WO3 is 5.16 ppm. In the youngest of Yenshanian granites, a light mica-albite granite has been identified, whose average WO₃ is as high as 242.3 ppm. From this line of evidence, the tungsten ore deposits in South China are considered to be genetically related to Yenshanian granites.

Wolframite-sulfide-quartz veins and scheelite skarns provide the bulk of the reserves and production. There are many different kinds of alteration associated with the different tungsten ore deposits, but the principal ones are silicification, greisenization, potash-feldspathization and chloritization.

 

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Preparing a fibrous structure of tungsten copper contact materials --- tungsten fibers (having a certain directionality) instead of tungsten powder, by two-dimensional weaving method, leaving a small amount of copper for the induction of copper, fiber and copper tungsten blank stack together, then place them in a vacuum sintering furnace for infiltration sintering, then fibrous tungsten can be obtained.
The diameter of sample 1 is 0.12mm, who is the fiber structure; sample 2 is WCu30 sintering by mixed powder; sizes of the two samples are 10mm * 10mm * 10mm.

Carry out arc erosion experiments by using TDR-40A vacuum single-crystal furnace, pure tungsten is anode, cathode is tungsten fibers after polishing, place the two electrodes in a vacuum chamber, placement: next anode, a cathode on. The voltage is 7400V; the maximum current is 80A. Anode move with 0.2mm / min speed to the cathode until the arc discharge, discharge waveforms recorded with an oscilloscope, and then transport to a computer. Wait until the release is finished, the cathode move up, in every arc 10 times, the samples were removed, using an accuracy of 0.1mg electronic balance measures the sample weight loss, repeat the above steps, each sample 50 times.

 

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