Ammonium paratungstate (APT) is crystallized from ammonium tungstate solution, so the preparation of ammonium tungstate is an important step in the APT production process. The preparation of ammonium tungstate solution is generally dissolving tungstic acid with ammonia water, and obtaining ammonium tungstate solution at 60°C.
The crystallization process of ammonium tungstate solution mainly consists of the crystal nucleus’s nucleation and growth. It is found that the cavitation and mechanical and other effects of ultrasonic wave have different degrees on the nucleation and growth of APT crystallization process.
Ammonium paratungstate (APT) prepared by ultrasonic method is mainly going through preparation of ammonium tungstate (AT) solution and ultrasonic strengthening or heating AT two processes, with the processes s as following:
1. Modulate tungstic acid slurry by adding hot water of 40~75℃, and then slowly add the slurry into the ammonia with a certain concentration which is being stirred constantly;
2. React for 3 to 4 hours by controlling the reaction temperature at 60℃ to make the complete dissolution of tungstic acid, filter to get ammonium tungstate solution after standing and clarify;
3. In the environment of ultrasound existing, the ammonium paratungstate crystal is prepared by neutralization or evaporation method, wherein the neutralization method is adding acid under the action of ultrasound, until the precipitate coming out in the solution; keep adding acid until the pH value of the solution is equal to 7.2, then obtain APT by standing, filtering and washing; while the evaporation method is using energy of ultrasonic wave to heat and evaporate ammonium tungstate for 30 minutes, and then get the ammonium paratungstate crystallized.