Preparation of ammonium metatungstate by thermal decomposition method using ammonium paratungstate as raw material:
After thoroughly mixing ammonium paratungstate with a small amount of citric acid catalyst, place it in a far-infrared rotary furnace, control the thermal decomposition temperature to 200-280 ℃, and decompose for about 1 hour. At this point, after removing some ammonia and water, the weight loss rate of ammonium paratungstate is 5% to 6%. After thermal decomposition, the product immediately forms a slurry, and an appropriate amount of ammonia water is added. The pH value is adjusted within the range of 3-4, and the slurry is boiled at 90 ℃. When the ammonium metatungstate content reaches 50% through evaporation and concentration, it can be sold as a liquid product. When the evaporation and concentration reach 20% of the original volume, the product is crystallized, filtered, separated, and granulated. The evaporated concentrate can also be dried by spray to obtain the product. If 45%~50% ammonium metatungstate is passed through the high-speed centrifugal rotary table spray dryer, the inlet hot air temperature is 250~300 ℃, and the outlet temperature is 90~95 ℃, the product is spherical crystal, the particle size is 200 mesh, accounting for 95%, and the free water content is less than 1.5%.
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