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.

 

Evaporation and crystallization is a process that feed liquid and solid of ammonium tungstate to get to oversaturation, which makes the material’s phase change and precipitate purified crystals from the solution. 

APT crystals precipitate from ammonium tungstate solution can be achieved, by that to adjust the PH of solution through loss of ammonia and get into the secondary salt formation region. The loss ammonia -adjust PH process can be achieved by evaporation crystallization process and neutralization crystallization process.

 

(1) It was found that with additional seed crystal, bulk density of APT has declined, which is consistent with the literature. It’s observed under a microscope that the particle size distribution is uneven and most are the coarse-grained polycrystalline. It’s reported that concentrate ammonium paratungstate to a certain proportion, add 1% to 2% the seed. Then constantly supplemented with solution, and prepare coarse APT. Concentrate the ammonium tungstate solution and gradually supplement with a solution to control the oversaturation, to prepared epigranular, large particle size APT.

 

(2) During the concentrating crystallization process, supplemented with water quantitatively and control oversaturation, the coarse crystalline regular APT can also be prepared. It is noteworthy that no more water in the crystallization terminal stages, or there will be a small amount of ammonium metatungstate with heating and stirring.