Ammonium paratungstate (APT) is an important intermediate product of the production of tungsten metal powder. To ensure the quality of tungsten powder, the average particle size, particle size distribution and crystal morphology should also meet certain requirements while the APT chemical purity does. With the rapid development of modern science and technology, there’re more and more demands for different grain size and shape of tungsten powder production, and thus the requirements of raw material APT are also getting higher. For APT crystallization conditions, the scholars have carried out extensive exploration and discussion, but the overall reports are rare, and the results are not entirely consistent. In order to investigate the basic conditions of APT production, for the preparation of APT crystallization problems, this article attempts to make some analysis and discussion on theory and the process practice based on a number of experimental studies made recently and some views are put forward by reference.

 

Evaporation and crystallization including the heating time (heating rate) and the evaporation time (evaporation rate). When the heating time is quick, most of the free ammonia in solution were expelled in a short time, so that PH of the solution decreased rapidly, and the over-saturation increases, and a lot of nuclei was formed rapidly, the particle size became finer. Long evaporation time, it will help small crystals dissolve constantly, big crystals continue to grow. the situation of crystal growth becomes more apparent when APT crystalline precipitate for a while before filtered. It was also found in the conditions of a certain degree of vacuum, evaporation speed increases, the bulk density of the resulting APT reduces significantly.