The preparation methods of ammonium metatungstate mainly include the following:
Ammonium metatungstate preparation method-solvent extraction method
Principle
Use organic extractant di(2-ethylhexyl) phosphate (D2EHPA) or tributyl phosphate (TBP) and kerosene solvent to form an organic phase, extract ammonium ions in ammonium tungstate, reduce the pH value to 2-4, and digest to generate ammonium metatungstate solution.
Steps
Mix the ammonium tungstate solution with the organic phase, extract the ammonium ions, and then obtain the ammonium metatungstate product through digestion, concentration crystallization, filtration separation and drying.
Features
It has high sensitivity and selectivity, simple equipment, rapid operation and good separation effect. However, the extraction solvent is volatile, flammable and toxic, so care should be taken during operation.
Ammonium metatungstate preparation method-ion exchange method
Principle
Use ammonium paratungstate as raw material to prepare ammonium metatungstate by ion exchange method.
Steps
Heat ammonium metatungstate at 130-140℃ for 1-8 hours, adjust the product into a slurry, boil at 80-100℃ for 2-6 hours to generate ammonium metatungstate solution. Then, the product is obtained through concentration, crystallization, filtration, separation, and drying.
Preparation of ammonium metatungstate – neutralization method
Raw materials
Use secondary ammonium metatungstate and nitrate as raw materials.
Steps
Add deionized water and ammonium citrate to form a slurry containing 12% to 30% WO3, add dilute nitric acid in a certain proportion, control pH value and temperature, and obtain ammonium metatungstate through heating, dissolution, aging, concentration, filtration, drying, and other steps.
Preparation of ammonium metatungstate – tungstic acid method
Principle
After dissolving tungstic acid with ammonia water, heat to remove ammonia under specific conditions to make the pH value reach 8, and further process to obtain ammonium metatungstate.
Steps
Add to boiling deionized water, heat to remove ammonia under stirring to make the pH value reach 8. Add acetic acid when the solution is boiling, then adjust the pH value to 2-4 with dilute nitric acid, continue heating and concentrating, cooling and filtering, drying and other steps to obtain the product.
Preparation of ammonium metatungstate – thermal decomposition method
Principle
After mixing ammonium paratungstate and a small amount of citric acid catalyst, thermally decompose at high temperature to generate ammonium metatungstate.
Steps
After fully mixing ammonium paratungstate and citric acid catalyst, put them into a far-infrared rotary furnace, control the decomposition temperature at 200-280℃, and the decomposition time is about one hour. The product is further treated to obtain ammonium metatungstate.
Preparation of ammonium metatungstate – electrodialysis method
Principle
Using ammonium tungstate or ammonium paratungstate as raw materials, ammonium metatungstate is prepared by electrodialysis.
Steps
Add ammonium paratungstate to the anode chamber. When the current passes, ammonium ions enter the cathode chamber through the anion exchange membrane, and the concentration of ammonium metatungstate in the anode chamber increases. Finally, the ammonium metatungstate solution is released from the cathode chamber and treated according to the above method to obtain ammonium metatungstate.
Among the above methods, neutralization method, tungstate method and thermal decomposition method are the main methods for industrial production in my country. In actual production, a suitable method can be selected according to specific needs and conditions to prepare ammonium metatungstate.
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