Chromium doped ammonium paratungstate may be produced by doping chromium (Cr) in evaporation crystallization process during the production of ammonium paratungstate. Adopting chromium acetate (CH3COO)3Cr (analytical reagent) and ammonium tungstate solution obtained by dissolving high-purity WO3 with ammonia water as raw materials to study the process of preparing APT powder by adding chromium acetate during crystallization. The result showed that:
1. Chromium mainly precipitated in the precipitation form of Cr(OH)3, which is prior to ammonium paratungstate, and the pH value at which precipitation started was equal or larger than 9. At around pH=8.5, the precipitation rate of chromium reaches a maximum, then the precipitation and dissolution of chromium near equilibrium state.
2. The precipitation of chromium in ammonium paratungstate is not saturated, and the content of chromium can be controlled to prepare ammonium paratungstate with different chromium content. The chromium content in APT increases linearly with the increase of the content of doping chromium.
3. The solubility of Cr(OH)3 in (NH4)2WO4 solution is larger than that in aqueous solution. The higher the WO3 concentration is, the lower the precipitation rate of chromium is.
4. Increase the initial NH4OH concentration and reduce the stirring rate can significantly increase the precipitation rate of chromium.
More details, please visit:
http://www.ammonium-paratungstate.com/english/index.html
