Ammonium Metatungstate Preparation by Spray Drying Method

Spray drying is a drying method that produces a powder drying product by processing a solution, emulsion, suspension and slurry material in a single process. The main advantages of this method are fast drying rate, short drying time and low material temperature. Its characteristics are that liquid raw materials can directly form powdered products, can be continuously produced in large quantities, without crushing process can directly get products with uniform particle size, excellent solubility and dispersion.

The disadvantage of using spray drying method to treat ammonium tungstate raw materials is that the particle size of the prepared ammonium tungstate particles is large. How can we improve the preparation conditions of spray drying, which can not be controlled and correlated with the morphology and particle size of ammonium tungstate?

When the spray dryer is an airflow spray dryer, the flow rate of the control gas is 400 to 1500L/h, the feeding speed is 5 to 50mL/min, and the outlet temperature of the exhaust gas is 70~130 degrees.

Ammonium carbonate and ammonium tungstate are mixed with 3 to 10 mixture of ammonium carbonate and ammonium tungstate at the same time, adding surfactants (the surface active agent can be one of ethylene glycol octyl phenyl ether, polyvinyl alcohol or sixteen alkyl three methyl ammonium bromide), and then the ammonium carbonate solution of ammonium tungstate with a mass fraction of 20% is prepared. The ultrasonic wave is oscillated for 10 minutes, and then imported into the spray dryer to control the hot air nozzle. The inlet temperature is 200 ℃, the controlled gas flow rate is 400 ml/min, the feeding rate is 30 ml/min, and the outlet temperature of tail gas is 70-130 ℃. After spraying and drying, spherical ammonium tungstate particles can be obtained. More than 95% of these particulates are hollow spheres.

After adding surface activity, the spray dryer can make full use of the advantages of surfactants, significantly reduce the surface tension of particles in spray drying process, prevent particle aggregation and limit the growth of particles, and reduce the particle size of ammonium tungstate microspheres.

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