How to prepare ammonium metatungstate crystal? Or how to prepare AMT crystal? There are various preparation methods, such as thermal decomposition method, neutralization method, solvent extraction method, tungstic acid method, ion exchange method, etc.
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Preparation of Ammonium Metatungstate Crystal by Thermal Decomposition
Mix ammonium paratungstate (APT) and a small amount of citric acid catalyst fully, put into a far-infrared rotary furnace to decompose at the temperature of 200-280 °C for about 1 h. Some ammonia and water are removed, and the weight loss rate of APT is 5% -6%. The thermally decomposed product is immediately slurried, supplemented with an appropriate amount of ammonia water, adjusted to a pH value of 3-4, and boiled to dissolve the slurry at 90 °C. It can be sold as a liquid product when it is concentrated by evaporation to 50% of APT content. When it is evaporated to 20% of its original volume, AMT crystals can be obtained by crystallization, filtration, and granulation. For example, 45-50% APT is passed through a high-speed centrifugal rotary disc spray dryer to obtain spherical AMT crystals. Wherein, the temperature of the inlet hot air is 250-300 °C and the temperature of the outlet is 90-95 °C.
