The main production processes for ammonium metatungstate hydrate include the following methods:
Neutralization method
Preparation of raw materials
Ammonium paratungstate and ammonium citrate are prepared into a slurry containing WO₃ 12% to 30% concentration.
Reaction process
According to the ratio of ammonium sec-tungstate to nitric acid 1:20, add 3%~5% dilute nitric acid to the ammonium sec-tungstate slurry, control the solid-liquid ratio 1:(3~4), pH 2~4, heat and dissolve, so that the relative density of the solution reaches 1.18~1.20.
Heating and reaction
Heating to 80 ~ 90 ℃, constant temperature and volume control pH value, stirring reaction for 4 hours.
Subsequent treatment
Aging for a few hours, the clear liquid is concentrated to WO₃ content of about 50%, filtered to remove insoluble matter, the clear liquid continues to concentrate, cooling crystallization, to 80 ℃ drying to produce products.
Tungstic acid method
Dissolving process
Dissolve tungstic acid with ammonia, add it into boiling deionized water, and heat up the ammonia under stirring to make pH=8.
Acidification process
Add acetic acid when the solution is boiling, and then adjust the pH 2~4 with dilute nitric acid.
Concentration and crystallization
Continue to heat and concentrate until the relative density is 1.5 to 2, stop heating, cooling and filtration. Add ethanol to the filtrate and stir well, filter after settling, dry and crush the crystals at 80℃ to get the product.
Thermal decomposition method
Raw material mixing
Mix ammonium paratungstate and a small amount of citric acid catalyst.
Thermal decomposition
Put into the far-infrared rotary furnace, control the temperature of thermal decomposition 200～280℃, decompose for about 1 hour.
Subsequent treatment
The product of thermal decomposition is immediately made into slurry, add appropriate amount of ammonia, adjust the pH value in the range of 3 ~ 4, boil the slurry at 90 ℃, and then the content of 50% ammonium paratungstate can be obtained after evaporation and concentration.
Solvent extraction method
Extraction process
Ammonium tungstate solution is extracted with organic extractant di(2-ethylhexyl) phosphate (D2EHPA) or tributyl phosphate (TBP) and kerosene solvent to form an organic phase to extract ammonium ion in ammonium tungstate, and then the pH value is lowered to 2～4.
Cooking and crystallization
Generate ammonium metatungstate solution by boiling, concentrate and crystallize, filter and separate, dry to get the product.
Ion exchange method
Heating and transformation
Heat ammonium paratungstate at 130～140℃ for 1～8 hours, adjust the product into slurry, and boil it at 80～100℃ for 2～6 hours to generate ammonium metatungstate solution.
Crystallization and drying
Then concentrate and crystallize, filter and separate, dry to get the product.
Electrodialysis
Electrodialysis process
Ammonium paratungstate is added to the anode chamber, when the current passes through, the ammonium ion enters the cathode chamber through the anion exchange membrane, and the concentration of ammonium metatungstate increases in the anode chamber.
Extraction product
Finally ammonium metatungstate solution is released from the cathode chamber.
More details of ammonium metatungstate product, please visit website: http://ammonium-metatungstate.com/
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