Over the last few years, sources of supply have changed dramatically. In 1986, the USSR was the world’s largest consumer but, by 1992, the reformed CIS was exporting tungsten and by 1996 was the world’s second largest supplier.

The other principal producing countries today are Austria, Bolivia, Peru and Portugal, whilst mines have closed in the last decade in Australia, Brazil, Canada, France, Japan, South Korea, Sweden, Thailand and the USA.

Not only have the sources of supply altered but so have the tungsten compounds traded, as fluctuating price differentials between concentrate and upgraded products and govermental restrictions played their part in the market.

Intermediate products include tungstates, tungsten oxides and hydroxides, W and WC powders, and ferrotungsten.

 

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Minerals

Tungsten occurs in the natural state only in the form of chemical compounds with other elements. Although more than twenty 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.

Deposits

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.

 

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Tungsten ore beneficiation methods are mainly hand-selected, HM election, re-election, flotation, magnetic separation and electrostatic separation. Wolframite in order to re-election dominated while scheelite flotation mainly associated. To the full recovery of useful components, improving the quality and tungsten concentrates recycling rate, currently the trend of dressing and smelting technology combined to increase the baking and Leaching and other hydrometallurgical refining methods.

Most tungsten metal recovery fine mud processing plant less than 50%. Sorting using tungsten fine mud shaker, belt chute with centrifugal concentrator. Single-use shaker sorting tungsten fine mud, the recovery rate is low. Since the 1960s the use of centrifugal concentrator, centrifugal ore – flotation, high intensity magnetic separation – flotation beneficiation process to make tungsten fine joint cement processing operations recovery rate of 10% to 20%.

 

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Tungsten ore beneficiation plant contained all kinds of crushers, such as jaw crusher (primary crusher), cone crusher (secondary crusher), impact crusher (Tertiary Crusher), vsi crusher (Sand Making Machine), etc. Different crushers based on raw material such hardness, humidity etc.

Tungsten crusher is a stone crusher used widely in ore crushing industry and ore mining industry. Ore crusher can reach the crushing ratio of 4-6 and the shape of final product is even. The ore crusher features reasonable structure, high productivity, easy operation and maintenance and safe performance.

Tungsten grinder mill also named ore grinding mill or ore grinder machine is a type industrial grinding mill used for grinding ore or ore materials. Ore grinder mill is an efficient tool for grinding many materials into fine powder. The ore grinding mill is used to grind many kinds of mine and other materials, or to select the mine.

 

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Tungsten smelting and fire refining method are two kinds of water law. The use of wolframite concentrate or smelting scheelite concentrate, but different smelting process, so both wolframite deposits, there scheelite, we must each ore body, each calculated reserves. When the ore wolframite, scheelite coexists 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 80C. The semi-solid is then baked at 135 to 145C 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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Tungsten ore low must be integrated mineral-rich concentrate to a smelting raw material. According to the type of tungsten ore dressing it can be divided 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 include 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 downhill , 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%.



 

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Silver tungsten electrode, namely silver tungsten bar or silver tungsten rod, from its name, we can know that it is the alloy of tungsten and silver. It can only be prepared by powder metallurgy method because of its low mutual solubility between tungsten and silver.Silver tungsten electrode owns the properties of high hardness, high arc corrosion resistance, high fusion welding resistance, and the like.

Silver tungsten electrode has a wide application, such as, machinery, switch through high current, sports equipment, high temperature resistance material, microelectronics material, aerospace and aviation. And its specifications are: AgW30 AgW40 AgW50 AgW55 AgW60 AgW65 AgW70 AgW75 AgW80 AgW85.

 

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Three tungsten electrodes welding performance comparison of the research experiment on the composite tungsten electrode table, as follows:

The above table shows that the amount of burning of the three kinds of electrodes are very small, which are inside the acceptable range (<0.050g), burning resistance performance of ternary complex tungsten electrode is better than cerium tungsten electrode, and the electrode B is slightly better than the electrode A; cerium tungsten electrode and electrode B are owning good arc performance, the electrode A has a general arc performance. This explains the type and amount of additives will have an impact on the performance of the tungsten electrodes. This is because different types of tungsten electrodes, its organizational structure is also different.

 

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RE tungsten rod, used as welding electrode, its main welding performance indicators are arc properties and burning properties performance, arc experiment and burning experiment are carried out on the welding machine.

Arc experiment
Experimental materials: positive, water-cooled copper block; negative, tungsten electrode;
Experimental conditions: arc at high frequency; arc when electrode current is 60A; arc duration time is 10s, stopped arc time is 30s; prepare three electrodes each grade, each electrode repeat 10 times.

Burning experiment: The purpose is to measure the change in weight before and after the welding electrode.
Experimental conditions: electrode welding current is 160A; arc duration time is 20min; prepare three electrodes each grade, take the mean value.

First observe and analyze its burning surface with a scanning electron microscope (SEM), and then dig the electrode along the longitudinal sample to obtain metallurgical samples, and electrolytic polishing and erosion with NaOH solution. Finally, observe and analyze the organizational structure changes of three internal electrodes in SEM and EDS.



 

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Experimental materials: A electrode (Y₂O₃: CeO₂: La₂O₃ = 1: 2: 1), B electrode (Y₂O₃: CeO₂: La₂O₃ = 3: 1: 1), cerium tungsten electrode.

Preparation of experimental electrode materials: Preparing rare earth tungsten billet by powder metallurgy method, add the rare earth rare in the form of earth nitrate solution (it should carry out several experiments to obtain the optimum amount - the total ratio of rare earth oxide in billet is 2% the amount of each rare earth oxides should meet the ratio, because when sintering, the loss of rare earth oxides vary each other) to blue tungsten oxide. Swaging rare earth tungsten billet repeatedly to the diameter of 3.8mm, and then stretching to a diameter of 2.0mm, and then after straightening, cut it into tungsten rod (length of 240mm). Polishing the end of the tungsten rod into cone (top diameter of 0.5mm), obtaining experimental electrode materials.

 

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