There are various production methods for ammonium metatungstate hydrate, which can be mainly summarized as follows:
Neutralization method
Prepare ammonium paratungstate and ammonium citrate into a slurry containing WO3 12%-30% concentration.
According to the ratio of ammonium secotungstate:nitric acid=1:20, add 3%~5% dilute nitric acid to the ammonium secotungstate slurry, control the solid-liquid ratio of 1:(3~4), and the pH value is between 2~4.
Heating to 80 ~ 90 ℃, constant temperature and volume control pH, stirring reaction 4 hours.
Filter to remove insoluble material, continue to concentrate, cooling crystallization, to 80 ℃ dry to produce products.
Tungstic acid method
Dissolve tungstic acid with ammonia, add it into boiling deionized water, and heat up the ammonia under stirring to make pH=8.
Add acetic acid while the solution is boiling, and then adjust the pH to 2~4 with dilute nitric acid.
Continue to heat and concentrate until the relative density of 1.5 ~ 2, stop heating, cooling and filtration.
The filtrate is added ethanol and stirred thoroughly, filtered after settling, and the crystals are dried and crushed at 80°C to obtain the product.
Thermal decomposition method
Mix ammonium paratungstate and citric acid catalyst fully, and then put into the far-infrared rotary furnace.
Control the thermal decomposition temperature at 200～280℃, decompose for about 1 hour.
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.
Cook the slurry at 90℃, and then get ammonium metatungstate by evaporation and concentration.
Solvent extraction method
Use organic extractant such as di(2-ethylhexyl) phosphate (D2EHPA) or tributyl phosphate (TBP) and kerosene solvent to form an organic phase to extract ammonium ion in ammonium tungstate.
The pH is reduced to 2-4, and ammonium metatungstate solution is generated by boiling.
Concentration and crystallization, filtration and separation, drying to produce products.
Ion exchange method
Heat ammonium paratungstate at 130～140℃ for 1～8 hours, and adjust the product into slurry.
Boil at 80～100℃ for 2～6 hours to produce ammonium metatungstate solution.
Then concentrate and crystallize, filter and separate, dry to get the product.
Electrodialysis method
Ammonium paratungstate is added to the anode chamber, when the current passes through, the ammonium ions enter the cathode chamber through the anion exchange membrane.
The concentration of ammonium paratungstate increases in the anode chamber, and finally ammonium paratungstate solution is released from the cathode chamber.
The above methods have their own characteristics and are suitable for different production conditions and needs. In the actual production process, it is necessary to choose the appropriate production process according to the raw material sources, equipment conditions, product quality requirements and other factors.
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