Development status of China's tungsten industry

Tungsten is known as “industrial MSG” and is a very important rare mineral resource. Tungsten and tungsten products have high melting point, high density and high hardness, and are widely used. Since the 19th century, tungsten is used for the first time since the production of alloy steel and hardened steel, which is a primary product from the deep to the processed product, has reached more than 20 species, including drill bits, cutting tools, alloys, chemicals, medicine, food To electronic devices, armor-piercing bullets, etc. Tungsten has become one of the irreplaceable materials in modern industrial society. The healthy development of the tungsten industry directly affects the development of the manufacturing industry and the national economy and military security. At present, many countries in the world attach great importance to the exploration and development of tungsten, and reserve tungsten as a strategic resource, and the development status of tungsten resources in China is worrying.

I. Status of tungsten resources in China

Tungsten rare element belonging to abundance in the crust is 1.1 × 10 -4%, mainly mineral wolframite and scheelite, China followed by tungsten, tungsten ore luminance.

The world has proven tungsten reserves of 2.9 million tons and reserves of 6.2 million tons. China's tungsten reserves are 1.8 million tons, and reserves are 4.2 million tons, ranking first in the world. See Table 1.

Table 1 Global tungsten resource reserves in 2003

Note: The data is from the US Geological Survey.

China's tungsten deposits are extremely rich, and there are 252 proven mineral deposits distributed in 23 provinces (districts), with Hunan (white tungsten ore) and Jiangxi (black tungsten ore) as the majority. 33.8% and 20.7%. However, in the past half century, some large and medium-sized mines have faced crisis: 9 large mines have 9 service years below 10 a. The over-exploitation of tungsten ore has caused the high-quality wolframite resources to be nearly exhausted, while more than 70% of the ammonium tungstate products in China are produced from the black tungsten concentrate. The current resources are mainly scheelite, accounting for about 73%, while the scheelite resources are characterized by associated and symbiotic ore, complex and difficult to choose. For example, the recovery level is higher in the domestic Shizhuyuan tungsten mine. The recovery rate of mining is only 36%, the recovery rate of ore dressing is only 63%, the grade of ore is low, and the impurity content is high. Among the middle ore produced by Luanchuan Mine (WO 3 mass fraction 53.5%), w(Mo)/w (WO 3 >5, more than 90 times of the standard concentrate; in the concentrates produced by other mines, As, P, Si, Sn and other impurities are high, tungsten products are sold in large quantities, and resources are wasted.

Second, China's tungsten industry overview

The tungsten industry is divided into several vertically related stages according to tungsten products (as shown in Figure 1): exploration, mining and smelting, processing to sales (export/domestic production plants). These vertical correlation stages can be completed by different independent companies, but from the development history of the tungsten industry, the development trend is that the vertical stages are united and operate along the chain from production to sales.

Figure 1 Tungsten industry chain by product

China's tungsten industry has a history of 100 years of development. It is roughly divided into three stages: the first 30 years after the founding of New China, a relatively complete tungsten industrial system was formed; from 1981 to 2000, the tungsten metallurgy, processing and hard alloy industries developed rapidly. The product structure has undergone great changes, changing the export situation of a single tungsten concentrate; after the 21st century, the development of the tungsten industry has entered a new era.

The rapid development of the tungsten industry has revealed more and more problems: 1) excessive exploitation of tungsten mineral resources; 2) high fluctuations in domestic and international tungsten products; 3) development of upper, middle and lower reaches in the tungsten industry chain Equilibrium; 4) The whole industry is widely distributed, small in scale and low in concentration; 5) The products are single, high, sharp, deep, and few products are small, the independent innovation ability of enterprises is low, and the sense of innovation is not strong. The existence of these problems has seriously affected the healthy and orderly development of China's tungsten industry, threatened the development of China's manufacturing industry and production safety, and greatly reduced the overall international competitiveness of China's tungsten industry.

Third, tungsten industry market and industrial policy

(1) Tungsten market conditions

Development of national economy stimulating the development of the rapid development of leading industries, building materials, automobile, steel, machining, diamond, electronics, engineering machinery and other industries, new areas of application development, all contributed greatly increased consumer demand for tungsten. In 2006, the annual output of crude tungsten wire and tungsten rod was 2102t, the amount of tungsten used for tungsten alloy electrode was about 650t, the amount of tungsten used for high-density tungsten alloy was about 850t, and the amount of tungsten used for chemical and other products was about 870t. The consumption structure of tungsten is: cemented carbide 48%, tungsten special steel 28%, tungsten 19%, chemical 5%. In 2006, the total consumption of tungsten in various fields was 18 623 t, which was 2.38% higher than that in 2005 (18190 t).

In recent decades, the overall technical level of China's tungsten industry has gradually improved. Since the 1980s, the export structure of tungsten products has undergone major changes, and the situation of simply exporting tungsten sand has been completely reversed. By the year 2000, tungsten concentrate has not been exported. Exports of minerals, primary products and tungsten intermediate products are also declining year by year, while exports of tungsten products with higher processing levels and cemented carbides representing the advanced level of the tungsten industry are increasing year by year (see Table 2). The deep processing of tungsten into the international market is an effective way to change the resource advantage to the industrial advantage, which indicates that the structure of China's tungsten industry is developing in a rational direction.

Table 2 Exports of tungsten products from 2002 to 2006 t

China is a big country in tungsten production and a major consumer of tungsten. According to the report of the Secretary-General of the International Tungsten Association at the 16th annual meeting, in 2000, China's tungsten consumption was 10 000 tons, second only to Europe. Affected by the growing domestic and international economic forms, the demand for tungsten has grown rapidly. The supply of tungsten concentrate has been in short supply since the beginning of 2003. Although the supply of tungsten concentrate in 2005 reached an unprecedented 91,000 tons, it could not meet tungsten. The production needs of smelting and processing enterprises. Therefore, in 2005, China imported tungsten ore and tungsten concentrates to reach 6 086.7 t, and in 2006 further expanded to 12 274 t, an increase of 101.6%. At the same time, the volume of imported tungsten products has increased year by year, and the import price (t-tungsten) is also rising (Table 3). Although the total amount of imported tungsten has increased, since 2004, the amount of tungsten powder imported from China has decreased.

Table 3 Imports of China's tungsten products (including tungsten concentrates) from 2002 to 2006

(2) Industrial policy

From the perspective of resource protection and sustainable development, the state has proposed a series of tungsten industry policies, which have promoted the further development of China's tungsten industry in a standardized and orderly manner. In terms of export quotas, tungsten export quotas have been decreasing year by year; in terms of tax policy: On May 1, 2005, the Ministry of Finance and the State Administration of Taxation lowered the export tax rebate for tungsten and tungsten products (from 13% to 8%); From January 1st of this year, the export tax rebate for tungsten and tungsten products will be lowered again (from 8% to 5%); from November 22, 2006, tungsten concentrate processing trade will be banned; from September 15, 2006, The export tax rebate for tungsten products was all adjusted to zero; from January 1, 2007, the provisional tariff for primary tungsten products increased by 5% to 15%.

In terms of industry management, since 2005, the State Council has issued notices to strengthen the management of tungsten- tin- bismuth industry, comprehensively rectify and standardize the order of mineral resources development; governments at all levels have increased the comprehensive containment of unlicensed exploration and mining, and indiscriminate mining. Waste the destruction of mineral resources and other illegal activities. In more than a year, Jiangxi Province closed 29 tungsten mines with overlapping state-owned tungsten mines, backward mining and selection processes, wasting resources, and destroying the geological environment of the mines. It closed more than 60 tungsten processing enterprises without legal ore sources. Hunan Province has carried out centralized rectification of more than 30 key mining areas, banned illegal mines, and suspend production and rectification of mines with illegal activities. In 2005, the General Office of the State Council issued Document No. 38 of the State Council, proposing to strengthen the management of tungsten-tin-bismuth industry, strengthen industry access and product export management, formulate regulations and regulations, prevent low-price competition and vicious competition, and improve the self-discipline level of the industry.

Fourth, product development

(1) Alloy steel

A large part of tungsten is used to produce special alloy steels, the most important of which is high-speed cutting steel. This steel generally has a W mass fraction of 8% to 20%.

High-speed cutting steel can be used to make a variety of tools, such as sharpening, milling cutters, dies, stampers, pneumatic tool parts, and more. Other grades of tungsten steel and chromium tungsten steel (1% to 6% W, 0.4% to 2.0% Cr) are also widely used.

Tungsten is also the main component of magnetic steel. There are two kinds of magnetic steel: tungsten magnetic steel and tungsten cobalt magnetic steel. Compared with non-alloyed magnetic steel, magnetic steel has strong magnetic and coercive properties. Tungsten-cobalt magnetic steel (5%-9%W, 30%-40% Co) has higher magnetic and coercive force.

(2) Cemented carbide based on tungsten carbide

Cemented carbide is known as "industrial teeth", and tungsten carbide is the main raw material for the preparation of cemented carbide. Nanocrystalline cemented carbide is a new tool material developed in recent years. It is based on nanometer WC powder and has high hardness and high hardness under the condition of adding appropriate binder and grain growth inhibitor. Hard alloy material with wear resistance and high toughness.

Tungsten carbide is a new functional material with high hardness, high thermal stability and high wear resistance. WC powder and bonding metal (Co, Ni, Fe, Fe-Ni, Ni-Co, Fe-Ni-Co, etc.) Sintered WC-based hard alloys can be widely used in the production of special tools, micro drills, printing needles and precision molds. With the development of ultra-fine cemented carbide, it is widely used for finishing difficult-to-machine materials, micro-drills for manufacturing printed circuit boards, printing needles for dot matrix printers, and precision molds.

The most important application of nano-carbide powders is in the manufacture of dense materials. The microstructure of the cemented carbide prepared by using the nano-composite powder has no abnormally grown crystal grains, thereby ensuring extremely high chemical uniformity, and the alloy has excellent crack resistance, so that the wear resistance thereof is remarkably improved. The results of the micro-drill wear test for the printed circuit board drilling show that the wear rate of the nanostructured WC-Co alloy drill bit is about 2.9 times that of the standard microcrystalline alloy drill bit for a given life. In addition, nano-hard alloys are widely used in cutting tools, rock drills, wear parts, bearings, etc. Medical scalpels, tape cutters, high-performance saw blades, etc. are examples of typical applications. Nano WC-Co composite powders have also shown good results as wear-resistant coating materials. The low-porosity wear-resistant coating can be prepared from the nano-WC-Co composite powder by thermal spraying, which significantly improves the performance of the hard alloy wear-resistant coating. Another use of nano-WC-Co composite powders is as a bonding material for micro-structured WC particles. This composite powder bonds micron WC structural particles together to produce a two-state structure (coarse WC grains and fine WC grains) to improve wear resistance in corrosive media.

(3) Contact point alloys and high-density alloys

The tungsten- copper composite material prepared by the powder metallurgy method (10%-40% Cu) has the advantages of high electrical and thermal conductivity, good arc erosion resistance, fusion resistance, low expansion coefficient, high strength and hardness, and is manufactured. Ideal contact materials for vacuum switchgear, electroformed electrodes, electronic packages and heat sinks, nozzle throat liners for rocket missiles.

Alloys containing 90% to 95% W, 1% to 6% Ni, and 1% to 4% Cu have a density of 17 to 19, which is called a high-density alloy and has the following advantages: 1) high strength: up to 1300 to 1500 MPa; 2) Good plasticity: W-Ni-Cu series is lower than the W-Ni-Fe series of the corresponding components, and the elongation of the W-Ni-Fe series sintered state can reach 10% to 15%, dehydrogenation by vacuum or atmosphere. After treatment, the elongation rate can reach 20% to 30%; 3) strong radiation absorption capacity: the radiation absorption capacity is 30% to 40% higher than lead , and has good rigidity, is not easy to be deformed during use; 4) corrosion resistance High temperature oxidation resistance: Good corrosion resistance to acid, no obvious oxidation below 500 °C, good strength and hardness at 800 °C or higher; 5) Good machinability: better Ductility and plasticity, can be machined, milling, grinding, planing, drilling, tapping and other machining, and large deformation strengthening treatment such as rolling, swaging and forging; 6) good electrical and thermal conductivity, low thermal expansion coefficient: The thermal conductivity is 5 times that of die steel, the thermal expansion coefficient is only 1/2 to 1/3 of iron or steel, and it has good electrical conductivity, corrosion resistance, high pressure resistance and other properties. Strong ability: good impact toughness, up to 50 ~ 100J / cm 2 ; penetration ability is greatly enhanced than hard alloy, in the kinetic energy armor-piercing projectile and armor material has a wide application prospects.

In view of a series of excellent characteristics of high-density tungsten alloys, it has been widely used in aerospace (navigation gyroscopes, balance blocks, shock absorbers, etc.), important components in the military industry (armor-piercing projectiles, penetration bombs, nuclear submarines, armor materials, etc.) ), it is also widely used in the civil industry such as machinery, electrical appliances, instruments and even medical and sporting goods.

(4) Processing of tungsten materials

There are many kinds of tungsten products, and the production process is different. The production enterprises can be divided into three types: the first one is the whole process production enterprise from ammonium paratungstate to tungsten processing materials, and the scale is larger; the second one is to purchase tungsten powder, and the key manufacturing The special processing enterprises of special tungsten products are medium-sized; the third type is a segment processing enterprise that purchases various tungsten billets or semi-finished rods, rods, wires and plates, and is restructured. The production technology of the first type of enterprise plays a leading role in the whole industry. For example, the mainstream technology used in the production of doped tungsten wire has reached the world level; the second professional production plant and research unit also has many advanced equipment and technology, which can produce various kinds. Shape and specification of tungsten products.

Tungsten products are diverse. Nano-tungsten has special applications in microelectronics and microscopy: tungsten tips with diameters between tens and a few microns are used for micro-drilling of large-scale integrated circuit boards; tungsten tips of diameter micron are used As a microprobe; the tungsten tip that is electrochemically etched to about 100 nm is used as a cold field emitter for field emission electron microscopy; tungsten nanowires can be directly used as tip tip for STM tip and micro force testers. head. Special specifications of tungsten materials have extra wide, extra long plates, ultra-thin, ultra-thin platinum , extra-thick bars, extra large, extra small pipes, extra-fine white straight wire, shaped parts and composite parts.

(5) Tungsten compounds

1, ZrW 2 O 8 thermal shrinkage material

ZrW(Mo) 2 O 8 is currently the most excellent thermo-shrinkable compound (having an ultra-low expansion coefficient and can adapt to large changes in ambient temperature), and has attracted great interest from crystal structure to heat shrinkage properties. The technical importance of ZrW 2 O 8 is mainly reflected in: 1) the isotropic cubic phase in the temperature range of about 100 ° C, so the heat shrinkage is always isotropic; 2) the heat shrinkage is high, so control of high coefficient of expansion (e.g., aluminum oxide) ceramic without destroying its excellent technical performance; 3) compound is heat-shrinkable and rare near room temperature, to fill the gaps in the room heat shrinkable compound interval. ZrW 2 O 8 has broad application prospects in high-tech fields such as aerospace technology, large-scale electronic integrated circuits, precision instrumentation, and high temperature and sealing technology.

2, WS 2 lubricating material

As a fine chemical, tungsten disulfide is not only a catalyst but also an important lubricating material. It is not only suitable for lubrication under normal conditions, but also suitable for lubrication under harsh conditions such as high temperature, high pressure, high vacuum, high load, radiation, corrosive medium, etc., even for computer and magnetic recording systems, medical applications. A moving part or the like that needs to be implanted in a living body. In 1997, hollow fullerene nano-WS 2 was introduced. Unlike the general layered structure of WS 2 , its cage structure can roll on the lubricating surface instead of sliding, thus having ultra-low friction and wear properties. Studies have shown that this new nano-WS 2 lubricant is widely used in space technology, ultra-vacuum and high vacuum, and automotive.

3. WO 3 functional materials

(1) WO 3 gas sensitive material. WO 3 is a very important functional material and has broad application prospects in gas sensors, displays, architectural dimming windows, and the like. WO 3 is a highly sensitive gas sensitive material, especially sensitive to gases such as nitrogen oxides, hydrogen sulfide, ammonia, and hydrogen. Nano WO 3 has superior gas sensing properties, and various gas sensors have been developed. Huang Shizhen and other gas sensing elements made of nano WO 3 (10 ~ 100nm) have high selectivity and sensitivity to low volume fraction of H 2 S. Wei Shaohong and other nano-WO 3 sintered gas sensors have good sensitivity, selectivity and response to NO 2 at lower operating temperatures.

(2) WO 3 nanometer film color changing material. The WO 3 film is the most superior electrochromic material discovered so far, and the nanostructured WO 3 film is more remarkable. It can not only be electrochromic, photochromic, but also gas-chromic. It can be used as the core material of gas sensing devices, in building and automotive energy saving, information display and storage, environmental monitoring, food industry and military. Good application prospects.

4, catalyst

In the field of chemical catalysis, tungsten compounds have important applications. Tungstic acid can be used as a catalyst for preparing high n-octylbenzene, and tungsten disulfide can be used as a catalyst for synthetic gasoline, and ammonium metatungstate can be used as a catalyst for production. In addition, recent studies have found that WC is a promising catalyst for hydrogenation, dehydrogenation, isomerization and hydrocarbon conversion and synthesis reactions; in the field of electrochemistry, WC is hydrogen ionization and The hydrogen evolution reaction has broad application prospects; WC can be used in fuel cells and hydrogen ionization electrodes to reduce or replace rare metal catalysts such as Pt, and solve the problem of catalyst poisoning; WC is also widely used in other chemical catalysis fields.

V. Conclusion

China's tungsten industry has a history of 100 years of development and has formed a relatively complete industrial system. China's tungsten resource reserves are the world's first, but the irrational application of resources and the various problems exposed during the development of the tungsten industry have seriously affected the healthy and orderly development of the tungsten industry. Fortunately, the country has introduced a number of rectification policies and has achieved results. Tungsten and tungsten products are widely used in various fields of social life due to their high melting point, high density and high hardness. Developing new product markets, consolidating the old product market, and expanding the application fields of tungsten and its compounds are the current development direction of the tungsten industry. China's tungsten industry should adhere to the concept of sustainable development, strengthen management legislation, establish a scientific and rational management system and operational mechanism, further optimize the industrial structure, improve the scientific and technological content and added value of products, and enhance the competitiveness at home and abroad.

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