Preparation
Industrially, ammonium tungstate is mainly prepared by evaporation, which involves dissolving industrial grade II ammonium polytungstate in ammonia water and then evaporating it for crystallization. However, due to the relatively high liquid-to-solid ratio during ammonia dissolution and the excessively long evaporation time, impurities (such as iron) are introduced into the ammonium tungstate solution due to prolonged stirring in a stainless steel reactor. Furthermore, uneven temperature gradients and alkalinity mass transfer cause different growth rates of the ammonium tungstate particles, leading to crystal encapsulation and impurity inclusion. This reduces the purity of the ammonium tungstate product, making it difficult to exceed the national standard (GB/T 10116-2007) grade 0, or even grade 1. This fails to meet the growing demand for high-purity and ultra-pure ammonium tungstate in the electronics industry, chemical synthesis, and petroleum catalysis sectors.
Uses
Ammonium Paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Other applications are in the fields of absorbent gels, coloring agent in the porcelain industry, and the catalyst industry.
