Ammonium Metatungstate Preparation--Thermal Degradation Method (2)
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- Category: Tungsten Information
- Published on Wednesday, 26 July 2017 11:05
The method of thermal degradation is the preparation process of ammonium metatungstate with Ammonium Paratungstate (APT) as raw material.
This method is also the main process for preparing Ammonium Metatungstate (AMT) at present. The thermal degradation method mainly controlls the calcination temperature of ammonium paratungstate and the depressurization of ammonia and water vapor, the ammonium paratungstate is thermally degraded to form an amorphous substance with water soluble ammonium metatungstate. The ammonium metatungstate solution was prepared by hydration, and the ammonium paratungstate solid was obtained by concentrating the solution and cooling crystallization.
Temperature control is the key factor for thermal degradation method. The suitable temperature range of ammonium metatungstate (AMT) prepared by ammonium paratungstate (APT) thermal degradation method is between 210°C and 265°C. In industrial production, the pyrolysis temperature controlled by different fatories is different from 210°C to 300°C. In fixed-bed units, APT material layers are thick, heat transfer rate is low, so the control temperature must be higher. In the rotary calcining furnace, APT is in motion state, the heat transfer effect is good, and the temperature is uniform, so the temperature can be lower. After comprehensive comparison, we found that the rotary calcining furnace is more suitable for preparing ammonium metatungstate because of its uniform temperature.
The rotary calcining furnace is the main equipment in China for preparing ammonium metatungstate. As the control accuracy is not high, pyrolysis conversion rate is generally around 80%. In recent years, Americans have made a number of improvements to the rotary calcining furnace, upgraded the multiple hearth furnace tube and upgraded the AMT recovery to 95%.
After pyrolysis, the non ionic water pulping was pre heated to 60°C - 80°C, and the pulp was heated to 90°C - 100°C, hydrated acidity control in pH 3-4, hydration soaking for 4 hours, removed by insoluble, filtrate to evaporation and concentrated to the original volume of about 1/3, AMT concentrated solution after cooling, finally get the AMT crystal.
Read more:http://news.chinatungsten.com/en/tungsten-information/97170-ti-12443
[ Ammonium Metatungstate Preparation -- Thermal Degradation Method (1) ]
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