Ammonium Paratungstate Producing Ammonium Metatungstate
Ammonium paratungstate (APT) thermal decomposition method producing ammonium metatungstate is the typical and main process to produce AMT by solid phase transition method which is the mostly common used.
By control ammonium paratungstate （APT） thermal decomposition temperature and partial pressure of ammonia and water vapour, APT will decomposed into ammonium metatungstate with fine solubility. Then by hydration to produce ammonium metatungstate solution, after cooling down and crystalline can get AMT product.
APT thermal decomposition reaction chemical equation:
5(NH4)2O·12WO3·5H2O=3(NH4)2O·12WO3·3H2O+4NH3↑+4H2O↑
Research shows that ammonium thermal decomposition temperature is 210℃, weight loss ratio is 3.34%, it is accordance with losing 4 NH3 and 4 H2O then converts to AMT molecular. When temperature is over 265℃, there appears the biggest endothermic peak. It means the proper temperature for ammonium paratungstate thermal decomposition method producing ammonium metatungstate is 210~265℃. However, in actual production, its thermal decomposition temperature will have deviation, even reach 300℃, it is related to the equipment. In order to promote the conversion rate, using thermal decomposition equipment of uniform heating is very important.
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