There are various production methods of ammonium metatungstate hydrate, which can be mainly summarized as follows:
- Neutralization method:
o Prepare ammonium paratungstate and ammonium citrate into a slurry containing WO3 12% to 30% concentration.
o Add 3%～5% dilute nitric acid to the ammonium secotungstate slurry according to the ratio of ammonium secotungstate:nitric acid=1:20, control the solid-liquid ratio of 1:(3～4) and the pH value between 2～4. o Heat up to 80～90℃, and then add the ammonium secotungstate and ammonium citrate into the slurry. o Add the ammonium secotungstate and ammonium citrate into the slurry.
o Heating to 80 to 90 ℃, constant temperature and volume control pH, stirring reaction for 4 hours.
o Filter to remove insoluble material, continue to concentrate, cooling crystallization, to 80 ℃ dry to produce products.
- Tungstic acid method:
o Dissolve tungstic acid with ammonia, add it to boiling deionized water, and heat the ammonia under stirring to make pH=8. o In the case of boiling solution, add the ammonia to the boiling deionized water.
o Add acetic acid while the solution is boiling, and then adjust the pH to 2-4 with dilute nitric acid.
o Continue to heat and concentrate until the relative density is 1.5 to 2, stop heating, cool and filter. o Add ethanol and stir well.
o Add ethanol to the filtrate and stir thoroughly, filter after settling, dry and crush the crystals at 80°C to obtain the product.
- Thermal decomposition method:
o Mix ammonium paratungstate and citric acid catalyst sufficiently and put into the far infrared rotary furnace.
o Control the temperature of thermal decomposition at 200～280℃ and decompose for about 1 hour. o After thermal decomposition, the product is immediately made into a product.
o The product of thermal decomposition is immediately made into slurry, add appropriate amount of ammonia, adjust the pH value in the range of 3 to 4. o Cook the slurry at 90℃.
o Cook the slurry at 90 ℃, after evaporation and concentration can be obtained ammonium metatungstate.
- Solvent extraction method:
o 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 ions in ammonium tungstate. o Reduce the pH to 2～4 range.
o Reduce the pH to 2 to 4, and generate ammonium metatungstate solution by boiling.
o Concentration and crystallization, filtration and separation, drying to produce the product.
- Ion exchange method:
o Heat ammonium paratungstate at 130～140℃ for 1～8 hours, and adjust the product into slurry.
o Boil at 80～100℃ for 2～6 hours to produce ammonium metatungstate solution. o Then concentrate and crystallize, filter and dry.
o Then concentrated and crystallized, filtered and separated, dried to get the product.
- Electrodialysis method:
o 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.
o The concentration of ammonium metatungstate in the anode chamber increases and finally ammonium metatungstate 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 a suitable production process according to the raw material source, equipment conditions, product quality requirements and other factors.
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