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 and 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.

When the impurities contained in ammonium tungstate solution is not too high, the influence on crystal grains is not obvious. test taking into account the normal production, the amount of ammonium chloride in ammonium tungstate solution prepared by ion exchange method was quite different from the one prepared by classic method. 

 

Tests showed that the higher the content of ammonium chloride in the original solution(increased from 10g / L to 100g / L), the finer the particle size of APT (bulk density decreased from 2.1g /cm3 to 1.8g /cm3). The reason may be that there are other substances that have grain adsorption in the solution, but do not participate in the crystalline lattice forming other substances. Since this impurities are adsorbed to the crystal surface, covering the active region of the crystal surface, leaving the crystal growth rate slow, hindering obtain coarse crystalline particles, but beneficial for obtaining fine crystals. 

 

It was also found that if there are solid impurities such as crystalline particles in solution, these particles play a central role in agglomerating to promote early nucleation generation. Different impurity content makes different products in crystal types and thickness. pure ammonium tungstate solution is easy to prepare regular polymorph and even coarse grain, and the physical properties of APT has better results in actual use.