The principle of preparing ammonium metatungstate by tungstic acid method is mainly based on the control of chemical reaction and solution properties. The following is a detailed explanation of the principle and steps:
Principle of Ammonium Metatungstate Preparation by Tungstic Acid Method
The preparation of ammonium metatungstate by the tungstic acid method mainly utilizes the reaction between tungstic acid and ammonia to convert tungstic acid into ammonium metatungstate by adjusting the pH value of the solution. This process involves the change of tungsten element’s valence and ion exchange, and the target product ammonium metatungstate is finally obtained.
Steps for the preparation of ammonium metatungstate by tungstic acid method
Dissolution of tungstic acid
Tungstic acid is added to boiling deionized water and dissolved by heating and stirring.
Addition of ammonia
Ammonia is added to the tungstic acid solution to carry out a neutralization reaction. In this process, the ammonia reacts with the tungstic acid to form tungstate, and at the same time releases hydrogen ions, making the solution acidic.
Adjustment of pH
The pH of a solution is adjusted by adding acetic acid or dilute nitric acid. Acetic acid lowers the pH of the solution, while dilute nitric acid further accurately adjusts the pH to a range of 2 to 4.
Within this pH range, the conversion of tungstic acid to ammonium metatungstate can proceed smoothly.
Heating and Concentration
The pH-adjusted solution is heated and concentrated, so that the water in the solution evaporates and ammonium metatungstate is gradually precipitated.
Cooling and crystallization
During the cooling process of the concentrated solution, ammonium metatungstate will be further crystallized and precipitated.
Filtration and drying
The crystallized ammonium metatungstate is separated from the mother liquor by filtration, and then dried to remove the excess water to get the final product of ammonium metatungstate.
The principle of preparing ammonium metatungstate by tungstic acid method is to convert tungstic acid into ammonium metatungstate through the reaction between tungstic acid and ammonia, and utilize the adjustment of pH value to make tungstic acid into ammonium metatungstate. This process involves several steps such as chemical reaction, control of solution properties and physical operation. High quality ammonium metatungstate products can be obtained by precisely controlling the pH value and operating conditions.
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