Preparation of Ammonium Paratungstate (APT) with Coarse Grain by Evaporating Crystallization

In the past few years, many users of ammonium paratungstate (APT) have a more strict quality requirement in its quality, including particle-size and apparent density, crystal shape, etc. Thus, a new preparation of APT with coarse grain that meets the requirements of industry has been introduced.

Evaporating crystallization is a popular method to prepare ammonium paratungstate (APT) crystal from industrial ammonium tungstate solution. Here are the common procedures to produce APT: an ammonium tungstate solution with density of 1.20 ~ 1.28 g • cm ^-3 (about WO₃ 250~280 g • L ^-1) is evaporated in an enamel reactor at 80 ~ 90 ° C for 6~8 h to crystallize out ammonium paratungstate crystals with apparent density of 1.0 ~ l.4 g • cm ^-3.

Here’s the new synthesis process of ammonium paratungstate with coarse grain by evaporating crystallization:

The aqueous feed is industrial ammonium tungstate solution coming from the process of solvent extraction. During the experimental process, the aqueous feed was put into the opened evaporator designed by ourselves to be evaporated for 1~ 3 h. The APT crystal obtained was separated from the solution by filtering. After being washed with cool clean water, it was dried up at 80~90 °C. The particle size distribution was measured by Micron Photo Sizer SKC-2000 Measuring Unit. The apparent density was determined using Funnel method.

Here are some factors to control the preparation of coarse grained APT:  

1. higher temperature;
2. addition of seed crystals
3. air agitation
4. lower concentration of tungsten trioxide(WO₃)

The APT product can be obtained with a density of 1.8-2.2 g • cm ^-3 and particle size of 36-42 µm under the factors of AT 120-150 g • L ^-1 WO_3,  the 5 % amount of seed crystal is added and the process is 3h.

The APT crystals has been compared with some commercial APT samples. The APT produced has a shape of relatively regular cubic and even particle size. And it has a simple process compared to the usual process and a shorted period.

• < Prev
• Next >