The process and principle of preparing ammonium metatungstate hydrate by tungstic acid method can be summarized as follows:
Flow of preparing ammonium metatungstate hydrate by tungstic acid method
- Preparation of raw materials
Main raw materials
Tungstic acid (WO₃) and ammonia (NH₃-H₂O).
Prepare appropriate amount of deionized water as solvent as well as acetic acid (CH₃COOH) and dilute nitric acid (HNO₃) for pH adjustment.
- Dissolving and pH adjustment
Dissolving tungstic acid
Tungstic acid was added to boiling deionized water and gradually dissolved with ammonia to form ammonium tungstate solution.
Adjustment of pH
With the solution boiling, slowly add acetic acid and then adjust the pH of the solution to between 2 and 4 with dilute nitric acid. This step is critical because it controls the form of ions present in the solution and the direction of the reaction.
- Concentration by heating
The pH-adjusted solution is continued to be heated for concentration. With the evaporation of water, the concentration of ammonium metatungstate in the solution gradually increases. When the relative density of the solution reaches 1.5 to 2, the heating is stopped. This range is determined based on experiment and experience to ensure that the ammonium metatungstate in the solution reaches a certain concentration.
- Cooling, filtration and drying
The concentrated solution was cooled to room temperature and filtered to remove insoluble matter and impurities.
Ethanol was added to the filtrate for stirring and settling to further purify ammonium metatungstate. The filtration was then performed again to obtain a pure ammonium metatungstate solution or wet crystals. The wet crystals were dried at 80 °C to remove residual water and solvent. The dried crystals were pulverized to obtain ammonium metatungstate hydrate product.
- Product collection and testing
Collect the dried and pulverized ammonium metatungstate hydrate product and carry out quality inspection, including purity, particle size, moisture content and other indexes, to ensure that the product meets the relevant standards.
Principle of preparing ammonium metatungstate hydrate by tungstic acid method
The principle of preparing ammonium metatungstate hydrate by tungstic acid method is mainly based on acid-base neutralization reaction and solubility change.
Acid-base neutralization reaction
Ammonia as a basic solution reacts with tungstic acid (acidic oxide) to produce ammonium tungstate. In this process, ammonia provides hydroxide ions (OH-) that combine with hydrogen ions (H+) in tungstic acid to form water, while tungsten ions (W6+) combine with ammonium ions (NH4+) to form ammonium tungstate.
pH Adjustment
The pH of the solution is adjusted by adding acetic acid and dilute nitric acid to a range of 2 to 4, which is favorable for the formation and stabilization of ammonium metatungstate. pH control affects the equilibrium of ions in the solution and the direction of the reaction.
Changes in solubility
With the heating and concentration, the water in the solution gradually evaporates and the concentration of ammonium metatungstate gradually increases. When the concentration reaches a certain value, ammonium metatungstate begins to precipitate as crystals. This process utilizes the principle of change of solute solubility in solvent.
From the above process, the flow of preparing ammonium metatungstate hydrate by tungstic acid method includes the steps of raw material preparation, dissolving and adjusting pH, heating and concentration, cooling and filtering and drying, as well as product collection and inspection. The principle is mainly based on acid-base neutralization reaction and solubility change principle.
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