The principle of preparing ammonium metatungstate by neutralization method is mainly based on acid-base neutralization reaction and ion exchange. The following is a description of the principle:
Acid-base neutralization reaction
The neutralization method utilizes the neutralization reaction between acid and base to achieve the purpose of preparing ammonium metatungstate. In this process, hydrogen ions (H+) in the acid combine with hydroxide ions (OH-) in the base to form water molecules (H2O).
In the preparation of ammonium metatungstate, acids such as nitric acid are usually used to carry out neutralization reactions with raw materials such as ammonium sec-tungstate. By controlling the reaction conditions and adding the right amount of acid, the complete neutralization reaction can be ensured to obtain the desired ammonium metatungstate solution.
Ion exchange
The neutralization reaction involves ion exchange. During the reaction, the ions in the solution will be exchanged, so that some ions in ammonium paratungstate are replaced by the ions in nitric acid, thus forming ammonium metatungstate.
Ion exchange not only helps to achieve acid-base neutralization, but also helps to improve the purity and quality of the product. By precisely controlling the process of ion exchange, a purer and more stable ammonium metatungstate solution can be obtained.
Specific steps of the neutralization method
Ammonium sec-metatungstate and nitric acid are used as raw materials for neutralization reaction. Firstly, the ammonium sec-metatungstate is added with deionized water and ammonium citrate to form a slurry containing WO₃ 12% to 30% concentration.
Add 3%~5% dilute nitric acid to the ammonium sec-tungstate slurry according to the ratio of ammonium sec-tungstate-nitric acid=1:20, control the solid-liquid ratio of 1: (3~4), pH value of 2~4.
Heat to dissolve, so that the solution relative density of 1.18 ~ 1.20, heating to 80 ~ 90 ℃, constant temperature and volume control pH, stirring reaction for 4 hours.
After aging for a few hours, the clear liquid was concentrated until the WO₃ content was about 50%, and the insoluble material was removed by filtration.
The clear liquid continues to be concentrated, cooled and crystallized, and dried at 80°C to produce ammonium metatungstate.
Characteristics
Neutralization method is a simple, reliable and effective method to prepare ammonium metatungstate. It is widely used in chemical laboratories and industrial production, and can precisely control the purity and quality of the product.
Through the description of the above principles and steps, it can be seen that the process of preparing ammonium metatungstate by the neutralization method involves acid-base neutralization reaction and ion exchange, and the high-quality and high-purity ammonium metatungstate product can be obtained by precisely controlling the reaction conditions and parameters.
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