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


Tungsten Manufacturer & Supplier: Chinatungsten Online - http://www.chinatungsten.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

 

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.


Tungsten Manufacturer & Supplier: Chinatungsten Online - http://www.chinatungsten.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

 

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%.


Tungsten Manufacturer & Supplier: Chinatungsten Online - http://www.chinatungsten.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

 

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% .


Tungsten Manufacturer & Supplier: Chinatungsten Online - http://www.chinatungsten.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn