APT prepares AMT by thermal degradation, from the composition of the formula, the main task is the removal of four molecules of NH3, of which the important parameters affecting the conversion rate is temperature. According to the information reported, the pyrolysis temperature of APT varied, for example, LIMU ore selected for 300 ℃; Zigong Cemented Carbide factory selected for 230-250 ℃. The pyrolysis temperature in U.S. Patent is selected for 275-300 ℃. It shows that the pyrolysis temperature of APT is not only related to crystal structure, but also to the pyrolysis furnace structure. In the production operation, the heated condition of pyrolysis equipment and APT situation is different, so the plants do not have the same control of the temperature range. For example, in a fixed-bed pyrolysis furnace effect, APT material layer is thick, the heat transfer rate is low, so it’s necessary to increase the temperature. In the rotary kiln and fluidized bed roaster action, APT is in motion with better heat transfer, so it is reasonable to control at a low temperature range.

 

Factors affecting the conversion rate firstly is pyrolysis temperature. If the partial pyrolysis temperature is too high, the insolubles tungsten trioxide appears. If the partial temperature is too low, APT cannot remove the gas entirely(four NH3 and two H2O), and the insolubles increase. Clearly, according to the conversion process requirements, pyrolysis equipment of uniform temperature should be provided, which is the first condition to improve the conversion rate of APT. The second one is hydrated conditions of the pyrolysis, including temperature, acidity, etc., affecting APT conversion rate. Best acidity value of hydration generally is the pH = 3.6-4.2 for recommendations ; and hydration temperature requires higher.