There are mainly the following preparation methods of ammonium tungsten oxide:
- Preparation method of ammonium tungsten oxide-neutralization method
Neutralization method is a commonly used method for the preparation of ammonium tungsten oxide. The method takes ammonium sec-metatungstate and nitric acid as raw materials, and the specific steps include:
Add ammonium sec-metatungstate to deionized water and ammonium citrate to form a slurry containing WO3 12% to 30% concentration.
According to the ratio of ammonium sec-tungstate: nitric acid=1:20, add 3%~5% dilute nitric acid to the ammonium sec-tungstate slurry, control the solid-liquid ratio of 1: (3~4), and the pH value is between 2~4.
Heat to dissolve, so that the solution relative density of 1.18 ~ 1.20, and then heated to 80 ~ 90 ℃, constant temperature and volume control pH, stirring reaction for 4 hours.
After aging for a few hours, the clear solution was concentrated to a WO3 content of about 50% and filtered to remove insoluble matter.
Clear liquid continue to concentrate, cooling crystallization, and then dried at 80 ℃ to produce products.
Second, the preparation method of ammonium tungsten oxide – tungstic acid method
Tungstic acid method is also a method for the preparation of ammonium tungsten oxide. The specific steps of this method include:
Dissolve tungstic acid with ammonia and add it into the deionized water containing boiling.
Heat the ammonia under stirring to bring the pH to 8.
Acetic acid is added while the solution is boiling, and then the pH is adjusted to 2 to 4 with dilute nitric acid.
Continue to heat and concentrate until the relative density is 1.5 to 2, then stop heating.
After cooling, the filtrate was filtered, and the filtrate was added with ethanol and stirred thoroughly, settled and filtered.
Crystals at 80 ℃ drying, crushing that is the product.
Third, the preparation method of ammonium tungsten oxide – thermal decomposition method
Thermal decomposition method uses ammonium paratungstate as raw material to prepare ammonium tungsten oxide. Specific steps include:
Mix ammonium paratungstate and a small amount of citric acid catalyst sufficiently, and then put into the far-infrared rotary furnace.
Control the thermal decomposition temperature at 200-280°C and decompose for about 1 hour. At this time, some ammonia and water will be removed, and the weight loss rate of ammonium sec-tungstate is 5% to 6%.
The product of thermal decomposition is immediately formed into a slurry, replenished with an appropriate amount of ammonia, and the pH value is adjusted in the range of 3 to 4.
The slurry is boiled at 90℃ and concentrated by evaporation to 50% of ammonium metatungstate, which can be sold as liquid products. When the evaporation and concentration to the original volume of 20%, crystallization, filtration and separation, granulation products.
Can also be evaporated concentrate spray drying products, such as 45% to 50% ammonium tungstate through the high-speed centrifugal rotary spray dryer, in the inlet hot air temperature of 250-300 ℃, out of the tower under the conditions of the mouth temperature of 90-95 ℃, the products obtained for the spherical crystals, particle size of 200 mesh accounted for 95%, containing free water is less than 1.5%.
Fourth, the preparation method of ammonium tungsten oxide-solvent extraction method
Solvent extraction method uses organic extractant to extract ammonium ions from ammonium tungstate solution, and then prepare ammonium tungsten oxide. Specific steps include:
Ammonium tungstate solution with organic extractant (such as di(2-ethylhexyl) phosphate (D2EHPA) or tributyl phosphate (TBP)) and kerosene solvent to form an organic phase for extraction.
During the extraction process, ammonium ions are extracted by the organic phase, which reduces the pH to 2-4.
After boiling to generate ammonium metatungstate solution, and then concentrated crystallization, filtration and separation, drying to produce products.
- Preparation method of ammonium tungsten oxide-ion exchange method
Ion exchange method is also a method of preparing ammonium tungsten oxide. The method takes ammonium paratungstate as raw material, the specific steps include:
Heating ammonium paratungstate at 130 ~ 140 ℃ for 1 ~ 8 hours, the product will be adjusted to slurry.
Boiling at 80 to 100°C for 2 to 6 hours to generate ammonium metatungstate solution.
Then the product is concentrated and crystallized, filtered and separated, and dried.
In addition, there are other preparation methods such as electrodialysis, which have their own characteristics, and the suitable preparation process can be selected according to the actual needs and conditions.
In general, there are various preparation methods of ammonium tungsten oxide, and different methods are suitable for different production conditions and needs. In the practical application, we can choose the suitable preparation method according to the specific conditions to obtain high quality tungsten ammonium oxide products.
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