In all Ammonium Metatungstate production processes, the main process parameters or control points are relative density of solution, pH value, temperature, reaction time and so on.
The important process parameters or control points in the production process of ammonium metatungstate hydrate mainly include the following aspects:
- Neutralization method
- pH value: In the neutralization method, the control of pH value is crucial. It is usually necessary to control the pH value in the range of 2 to 4 to ensure that the reaction between ammonium sec-tungstate and nitric acid proceeds smoothly to produce ammonium metatungstate.
- Temperature: The control of temperature is also critical in the process of heating dissolution and stirring reaction. Usually the solution needs to be heated to 80～90℃ to promote the reaction.
- Stirring speed: the stirring speed has an effect on the homogeneity and efficiency of the reaction, and it is necessary to control the stirring speed appropriately to ensure that the reactants are fully mixed.
- Tungstic acid method
- pH value: in tungstic acid method, it is also necessary to control the pH value. After adding acetic acid, use dilute nitric acid to adjust the pH value to 2~4, which is the key to ensure the smooth running of the subsequent reaction.
- Temperature: In the process of heating and concentration, the control of temperature has an important influence on the quality and yield of the product. It is usually necessary to heat the solution to a certain temperature so that its relative density reaches 1.5 ~ 2 when the heating is stopped.
Third, thermal decomposition method
- Thermal decomposition temperature: In thermal decomposition method, the control of thermal decomposition temperature is the key. It is usually necessary to control the temperature in the range of 200～280℃ to ensure that ammonium sec-tungstate and citric acid catalyst fully react to produce ammonium metatungstate.
- Stirring and boiling: After the product of thermal decomposition is made into slurry, it is necessary to add appropriate amount of ammonia, adjust the pH value in the range of 3 to 4, and boil the slurry at 90℃. In this process, stirring and cooking conditions have an important impact on the quality and yield of the product.
Fourth, solvent extraction method and ion exchange method
- pH value: in the solvent extraction method and ion exchange method, the control of pH value is equally important. Usually need to reduce the pH value to 2 ~ 4, to ensure that the extraction or exchange process is carried out smoothly.
- Reaction temperature and time: In solvent extraction and ion exchange, reaction temperature and time are also key parameters. Appropriate reaction temperature and time need to be controlled to ensure the efficiency of the reaction and the quality of the product.
- Electrodialysis
- Current and voltage: in electrodialysis method, the control of current and voltage is the key. Appropriate current and voltage need to be controlled to ensure that ammonium ions enter the cathode chamber through the anion-exchange membrane, thus increasing the concentration of ammonium metatungstate in the anode chamber.
In summary, important process parameters or control points in the production process of ammonium metatungstate hydrate include pH, temperature, stirring speed, thermal decomposition temperature, stirring and cooking conditions, reaction temperature and time, current and voltage. The control of these parameters or control points has an important influence on the quality and yield of the product, so it needs special attention.
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