Metatungstate production methods more, can be divided into solid and liquid phase inversion transformation method two categories. Typical solid phase inversion process is based on the thermal degradation APT method as a raw material, this method is the main industrial production process of the AMT. The phase transformation method of ammonium tungstate solution as raw material, extraction, ion exchange, membrane electrolysis, or a method in the solution and the pH adjusted to the appropriate range, the obtained solution of ammonium metatungstate. Many research phase inversion method, is to develop in the direction of industrial applications.

Production of Thermal Degradation AMT

By controlling the APT and the pyrolysis temperature and the ammonia partial pressure of water vapor, the water-soluble pyrolysis APT metatungstate large amorphous material, and then hydrated into a solution of ammonium metatungstate, the solution was concentrated and cooling crystallization available AMT solid.

APT pyrolysis conversion rate and the temperature, if the pyrolysis temperature is too high, the resulting insoluble tungsten oxide is not, if the temperature is too low, the APT insufficient removal of ammonia and water (by Molecular Formula calculated APT be removed the four NH3 and 4 H2O), insolubles increases. APT suitable temperature to improve the conversion rate of the key.

Preparation of Ion-Exchange AMT

AMT ion exchange process to produce ammonium tungstate solution as raw material, ion exchange method because the process is relatively simple, easy to control, to avoid the formation of APT, not into the new contaminants, the process can be continuous, and thus has potential for development .

Extraction and ion exchange method originally buried in a similar, but in the extraction process is easy to produce solids resulting emulsion, industrial applications, there are certain difficulties. Silicic acid, and the solid is likewise prepared using ammonium tungstate solution, one way to take AMT, but due to the addition of silicic acid may cause contamination of the product AMT, so there is no industrial application. Ion-exchange membrane electrolysis (including ion-exchange membrane electrodialysis) is still in the development stage, to be developed better longer selective membrane, reduce production costs, to be applied to the production.


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Preparation of tungsten metal powder The main methods are: Preparation of tungsten metal powder, the main method

(1) hydrogen reduction of tungsten oxide;
(2) hydrogen reduction of tungsten halides;
(3) tungsten oxide or tungsten acid carbon reduction;
(4) tungsten oxide or metal tungstate thermal reduction method;
(5) molten salt electrolysis.

The most practical industrial method of hydrogen reduction of tungsten oxide. Tungsten halide (WCl6, WF6) can be prepared from hydrogen reduction of tungsten powder with special features, and was gradually extended application of other methods do not apply to the production of plastic tungsten.


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Tungsten oxide behavior at high temperatures

Tungsten oxide, can be stable in four: (1) tungsten oxide yellow; (2) blue tungsten oxide; (3) purple tungsten oxide; (4) of tungsten oxide Brown

Hydrogen Reduction of Tungsten Oxide Thermodynamic Analysis

WO3 +3 H2 = W +3 H2O The overall reaction is endothermic reaction, the temperature increases the equilibrium constant Kp = PH2O/PH2, is advantageous to the reaction. Temperature, the equilibrium concentration of water vapor in the gas phase increases, the reaction proceeds more completely.

Tungsten Oxide Hydrogen Reduction Kinetics Analysis

Thermodynamics of the reaction can be determined, but the actual process far from equilibrium conditions, WO3 hydrogen reduction process does not strictly follow the step by step to restore order. α-W and β-W is W two allotropic crystal. α-W is a cubic crystal, lattice constant of 0. 316nm; pW cubic crystal lattice constant of 0.5036nmoβ-W is the temperature below 823K from the WO2 reduction with hydrogen, which is characterized by a large chemical activity, spontaneous combustion . β-W converted to α-W transition temperature was 798K, does not occur α-W converted to β-W in the reverse transformation. β-W is tungsten atoms of the crystal, but due to the presence of impurities and lattice distortion.

Tungsten Powder Particle Size and Purity Influence Factors

Tungsten particles into a particle and the second particle. The primary particles is a single particle, is first generated and separated from each other and independent of the presence of the particles; secondary particles of two or more of primary particles with particle accumulation easily separated.

Tungsten powder particle size and purity influence of many factors, the following factors will be analyzed as follows: raw materials, water, impurity elements, hydrogen


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Acid decomposition method in principle can be used to decompose scheelite, wolframite can be used to decompose . Decomposed with acid concentrates obtained crude acid can be obtained and then the ammonia dissolved ammonium tungstate solution , this solution can be prepared by crystallization of the pure compound of tungsten APT . Therefore, the acid decomposition process concentrates with short process, low cost. Mineral raw materials such as tungsten high impurity content , and ammonia dissolved in acid decomposition alone purification is difficult to obtain high -purity products . Therefore acid decomposition method used for processing low impurity content of scheelite . If the process to make appropriate adjustments for the poor quality of scheelite ( tungsten containing 40% to 60 %, including CaCO3 and other minerals less susceptible to acid dissolution ) can also be acid decomposition method.

Hydrochloric acid, nitric acid can be used to decompose scheelite . However, economic benefits, production results and other factors to consider, at present is generally used industrially acid decomposition method .

Thermodynamic Analysis

Tungsten minerals and chemical reaction of hydrochloric acid , and hydrochloric acid scheelite occurs when the following chemical reactions : CaWO4 (s) +2 HCl (aq) = H2WO4 (s) + CaCl2 (aq)

Wolframite and hydrochloric acid reaction : FeWO4 (s) +2 HCl (aq) = H2WO4 (s) + FeCl2 (aq); MnWO4 (s) +2 HCl (aq) = H2WO4 (s) + MnCl2 (aq)

Production practice, each larger than the concentration of the reaction solution , the concentration equilibrium constant at this time has more practical significance. Concentration equilibrium constant can be measured directly by experiment .

Acid decomposition process, the mineral raw materials of impurity elements in different reaction conditions with different chemical behavior .

Iron: elemental iron in tungsten minerals usually FeWO4, FeS2, Fe2O3, Fe3O4 and other forms exist. Concentrate milling , may also be part of the metal into iron .

Mo : Mo ore mainly CaMoO4 and molybdenite (MoS2) exists in the form of calcium molybdate molybdenum reacts with hydrochloric acid

CaMoO4 +2 HCl = H2MoO4 + CaCl2

MoS2 not with hydrochloric acid , but in the presence of an oxidizing agent can react molybdate :

MoS2 +2 HCl +6 NaNO3 = H2MoO4 +2 Na2SO4 +2 NaCl +6 NO ↑

Molybdate in hydrochloric acid greater than the solubility , and with the temperature increase and the concentration of hydrochloric acid increases. Therefore, improving concentration of hydrochloric acid , can make most of the molybdenum and tungsten into the solution to achieve separation .

In the acid decomposition process , you can also add to the addition of molybdenum ferrosilicon . Ferrosilicon (SiFe) as a reducing agent , where the silicon does not play a role with hydrochloric acid , and the iron will be oxidized to iron ions.

2H2MoO4 + SiFe +8 HCl = 2MoOCl3 + FeCl2 + Si +6 H2O

Treatment of high molybdenum content scheelite , the mother liquor by concentration of hydrochloric acid by acid and adding a reducing agent (SiFe) approach to the removal of molybdenum . Controls the right conditions , in addition to molybdenum ratio can reach 80%.


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Many have studied the decomposition of tungsten mineral raw materials, in addition to several domestic and industrial production in the application of methods, chlorination and fluoride salt solution is also moving towards industrialization, while the high temperature carbonization melt extraction from the direct production of tungsten tungsten carbide technology have reached the industrial applications. In addition, the complexation of scheelite acid leaching method, EDTA sodium salt leaching method has also been reported.

Scheelite Chloride Leaching

Fundamental

Scheelite sodium or ammonium fluoride can be used to break down. Sodium fluoride and scheelite reaction following formula: CaWO4 (s) +2 NaF (aq) = Na2WO (aq) + CaF2 (s)

The use of NH4F + NH4OH as a leaching agent, the reaction with scheelite obtained directly (NH4) 2WO4 solution. At 225 ℃, the measured decomposition scheelite NaF concentration equilibrium constant Kc 24.5, and sodium carbonate decompose under the same conditions scheelite, measured Kc value of only 1.52, so the sodium fluoride and ammonium is oxidized one kind is more effective than sodium carbonate decomposition scheelite reagents. Scheelite NaF decomposition below 100 ℃ under the conditions of mineral particles CaF2 film formed on the surface, hindering further reaction; temperature higher than 100 ℃, the CaF2 film off, the reaction speed is mainly affected by the chemical reaction speed control.

Process and Lndicators

Zhen-Gang YAO White tungsten leaching tests carried out NaF, when the temperature is 190 ℃, NaF dosage is 1.2 times the theoretical amount, adding a small amount of additives, pressure cooking 1.5h, decomposition rate remained stable at around 99%. The resulting crude sodium tungstate solution containing P · As · SiO2 impurities is low, basically achieve the technical requirements after purification. For low molybdenum scheelite by NaF pressure cooking crude sodium tungstate solution can be directly used defluorinated plus molybdenum addition of acid curing agent. Obtained by extraction and crystallization APT quality can be reached international zero Need requirements.


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Chloride metallurgy is the recent development of the new technology , with the chlorination process tungsten mineral raw materials have a number of advantages , mainly in:

( 1 ) Chlorine is very active , and thus the decomposition rate is very high, high metal recovery , in addition to deal with the general tungsten , but also especially suitable for processing lean tungsten ore, tungsten fine mud , tungsten ore tailings and polymetallic composite ore.

( 2 ) low boiling point of many of the metal fluoride , there is a gap between each other , and thus the vapor pressure can be used for separation and purification of different , easily obtained pure tungsten chloride.

( 3 ) Hydrogen chloride reduction process for the gas-phase reaction , easily accessible from tungsten chloride to obtain fine tungsten powder or plating .

( 4 ) easy recovery of other valuable elements .

Therefore, the method is the decomposition of tungsten chloride mineral raw materials promising methods. At present chlorination is mainly used in the decomposition of tungsten alloy scrap tungsten and tungsten minerals and thus obtain fine tungsten powder, has small-scale production .

Fundamental

Professor Li Honggui materials under thermodynamic system draws 1100K when W-Cl-O system and Fe-W-Cl-O system thermodynamic equilibrium diagram . In the W-Cl-O system exists WO2Cl2, WOCl4, WCl2 other compounds , oxygen -bit systems is higher, the higher the content of mixed vapor WO2Cl2 , to get WCl4 or WCl2, must reduce the oxygen -bit system , to ensure adequate reducing atmosphere . Therefore, scheelite or wolframite chloride , often adding carbon as a reducing agent.

For scheelite such as the use of sulfur dioxide as a reducing agent , the reaction is : CaWO4 (s) + Cl2 (g) + SO2 (g) = CaSO4 (s) + WO2Cl2 (g)

Scheelite chloride decomposition using carbon as a reducing agent , such as , you must add a certain amount of calcium fluoride decomposition rate was high : CaWO4 (s) +3 C (s) +2 Cl2 (g) + CaF2 (s) = 2CaClF (s ) + WOCl2 (g) +3 CO (g)

Process Lndicators

Tungsten with carbon and mineral raw materials are first additive (CaF2) and binder mixed group ; system group for the purpose of the charge to ensure good air permeability , dehydration briquettes sufficiently dried , and then chlorination, chlorination process is usually vertical chlorination furnace , the temperature controlled at 600 ~ 800 ℃ ( different materials , chlorination temperature is not the same ) , the chlorination of a mixed oxide vapor is condensed , and then purified by means of separation , can be used to obtain pure tungsten chloride obtained by hydrogen reduction of tungsten powder or coating can also be hydrolyzed acid .

Wolframite use chlorine chloride , the temperature to 800 ~ 900 ℃ only when a full , but adding carbon as a reducing agent , the reaction starts 400 ℃ , 500 ℃ under faster , to 600 ℃ has chlorination more completely .

Scheelite plus carbon oxidation , if not additive CaF2, then at 600 ℃, tungsten chlorination rate of only 65% , if by adding the theoretical amount of calcium fluoride , ingredients of carbon and scheelite ratio of 0.075,600 ℃ chlorination of tungsten chloride rate up to 99% .


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The process is made ​​directly by the tungsten carbide, the former Soviet Union in this regard fruitful research. According to the Canadian Pacific International Industrial Co., Kirby said: used to produce tungsten carbide powder purity has reached 99.3% to 99.4%, while the cost of production of tungsten carbide with the traditional way of comparison can be reduced by half, so much attention.

Process and Principle

The process comprises three main technical steps: melt extraction, carbonation and the grinding gas into leaching purified.

(1) Melt Extraction

The tungsten and Na2SiO3, NaCl mixed and melted 1050 ~ 1100 ℃, the following reaction occurs:

2 (Fe, Mn) WO4 +3 Na2SiO3 +16 NaCl = 2 (Na2WO4 · 8NaCl) + Na2 (Fe, Mn) 2Si3O9

The resulting tungsten Na2WO4 · 8NaCl immiscible silicate phase, according to the density stratification, the upper silicate phases, the lower chloride - tungstate phase. The two phases were separated by decantation, the 98% to 99% of WO3 and a small amount of impurity in the titanium manganese tungstate phase.

In scheelite as raw material, Al2O3 and NaF should be added as a flux. But if the scheelite and wolframite 1:3 mix to join, you can add the free flux.

(2) Gas into Carbonized

The chloride - NaCl added tungstate scaling, and then in 1050 ~ 1070 ℃ when the pass into the natural gas, tungsten carbide reaction occurs as follows:

Na2WO4 +4 CH4 = Na2O + WC +3 CO +8 H2

(3) Purification Polishing Leaching

Tungsten periodically removed from the grinding and dispersion of salt furnace, first with 10% HCl and washed with 3% NaOH solution, extract, and then through the filter to remove impurities to get a more pure tungsten carbide powder.

Process Conditions and Indicators

Add the material ratio of: wolframite: NaCl: Na2SiO3 = 33:47:20; at 1050 ~ 1100 ℃ melted and incubated 2h, obtained chloride - tungstate phase substantially composed of: WO325% ~ 30% ; FeO about 0.24%; MnO about 0.3%; silicates containing approximately 0.5% WO3; WO3 recovery of this step to 98% to 99%.

The resulting molten chloride layered - tungstate phase and then in the 1050 ~ 1070 ℃ was passed through the gas, the main component of natural gas methane (CH4) in the utilization rate of approximately 2.2% carbon, 90% of WO3 are recovered into the WC, WC to ground and then acid leaching filtered to further remove impurities, the resulting WC WC carbide to achieve the general requirements.


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Most of the metal tungsten powder is used as a raw material for the production of tungsten carbide, so here describes a tungsten as a raw material, a direct method of producing tungsten carbide as the supplementary toner production methods are suitable.

In recent years, the development of the Russian Research Institute of Chemical Technology concentrates of the "furnace" aluminum thermal reduction method. Reliable naturally at high temperatures to restore directly from tungsten concentrate and make carbonation. Raw concentrates containing 55% ~ 60% WO3.

Aluminum thermal reduction of graphite, copper or steel crucible for, reduction and carburization process is very fast only 3 ~ 5min. The exothermic heat sufficient to melt all of the reaction product, and to a metal carbide-containing phase to obtain a good separation of the slag phase.

"Furnace" obtained by aluminothermic reduction of 55% tungsten metal phase containing 75% Fe 15% to 20%, the excess of the reducing agent from 1% to 4% of aluminum, the remaining metal impurities (Mn, Ni, Cu, etc. ) less than 2%, and a small amount of slag inclusions. CaO · 2Al2O3 slag phase and a mixture of CaO · Al2O3.
The metal phase crushed to 150μm, the obtained powder was acid leached to remove the acid-soluble substances, namely to obtain the final product tungsten carbide (WC).

X-ray diffraction analysis showed that the product contains only one phase WC. The chemical composition of tungsten carbide composite Russian technology standards TY48-19-265-91. WC product quality than traditional craftsmanship, carbonation completely free carbon content is reduced to 0.01% (typically less than 0.04%), the lattice defects are reduced, without W2C, Mo2C and Fe3W3C generation. Molybdenum scheelite lattice into the WC, do not generate separate Mo2C phase. It is very important to manufacture cemented carbide. WC impurity content of products (including Fe) meets the requirements, costs mean diameter of 9μm. Russia's experience has shown that the product can be used for drilling tools and carbide production.

High product quality, process simplicity and low cost of production is the production of tungsten carbide aluminum thermal reduction of the basic features. 


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