The process of preparing ammonium metatungstate hydrate by neutralization method can be clearly divided into the following steps, which are summarized with relevant figures and information:
- Preparation of raw materials
Main raw materials
Ammonium sec-metatungstate (APT) is used as the starting raw material.
Nitric acid or other suitable acid solution as neutralizer.
- Neutralization reaction
Preparation of slurry
Add ammonium paratungstate to deionized water and appropriate amount of ammonium citrate (or other suitable additives) to formulate a slurry containing WO₃ concentration of 12% to 30%.
Neutralization operation
According to the ratio of ammonium paratungstate to nitric acid (usually 1:20), add 3%~5% dilute nitric acid into the ammonium paratungstate slurry. Control the solid-liquid ratio in the range of 1:(3～4), and adjust the pH value to 2～4. Heat to dissolve, so that the relative density of the solution reaches 1.18～1.20, and the heating temperature is controlled at 80～90℃.
Constant temperature and volume reaction
Under the condition of constant temperature and volume, control the pH value and stir the reaction for 4 hours. After the reaction, let the solution age for a few hours for full reaction and precipitation.
Post-treatment
Concentration of clear solution
The aged clear solution was concentrated to bring the WO₃ content to about 50%.
Filtration and removal of impurities
Remove insoluble matter and other impurities by filtration to get pure ammonium metatungstate solution.
Cooling and crystallization
The concentrated ammonium metatungstate solution was cooled to crystallize ammonium metatungstate hydrate crystals gradually.
Drying
The crystallized ammonium metatungstate hydrate crystals are dried, usually at 80℃ to remove the residual water.
- Product collection and inspection
Product collection
Collect the dried Ammonium Metatungstate Hydrate products, package and store.
Quality Inspection
Perform quality inspection on the product to ensure that the purity and other performance indexes of the product meet the relevant standards.
The process flow of preparing ammonium metatungstate hydrate by neutralization method includes raw material preparation, neutralization reaction, post-treatment, product collection and inspection. By controlling the conditions of pH value and temperature of neutralization reaction, this method makes ammonium sec-metatungstate gradually transformed into ammonium metatungstate, and obtains pure ammonium metatungstate hydrate product through subsequent treatment. The method is simple, but attention needs to be paid to controlling the reaction conditions and post-treatment process to ensure the quality and stability of the product.
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