Ammonia Purification - Thermal Dissociation Method for Preparing High Purity Tungsten Trioxide

At present, the industrial production of pure tungsten trioxide or APT is mainly purify the crude sodium tungstate solution.

Ammonia purification of a thermal dissociation method is the South China University of Zhang Qixiao et al in the early 21st century proposed purification of ammonium arsenate solution method, it can be achieved by the crude ammonium tungstate solution directly prepared high purity tungsten trioxide.

The use of ammonia purification heat from the main base of high pure tungsten trioxide solution is directly preparing high purity tungstic acid (H₂WO₄), the quality of H₂WO₄ directly affects the quality of the final product and cycle times. The process of ammonia purification by thermal dissociation is:

1.The pulp industry H₂WO₄ slowly adding ammonia, WO₄ will dissolve (NH₄) ₂WO₄ solution, and silica, crude H₂WO₄ of ferric hydroxide, manganese oxide and calcium tungstate are reserved for ammonia dissolution in slag.

2.Filtered (NH₄) ₂WO₄ solution, after heating and removing ammonia, they gradually precipitate the solubility of ammonium paratungstate crystals. 

3.The ammonium paratungstate dissolved in ammonia, is in the temperature range of 250-350 °C ammonium paratungstate for a sufficient period of time to make the properties of ammonium paratungstate crystals change, and then can be dissolved in ammonia to produce (NH₄) ₂WO₄ solution. With the progress of the thermal dissociation process, the impurities in the crystallization of ammonium paratungstate were dehydrated and oxidized. Most of the impurities were insoluble in ammonia, and only aluminum, arsenic and phosphorus still entered (NH₄) ₂WO₄ solution.

4.The obtained (NH₄) ₂WO₄ and then a first evaporation crystallization, to consolidate the effect, in general, the solution and then evaporate the crystallization of ammonium paratungstate will be much higher than the first purity.

The ammonia purification process has simple equipment, high pure tungsten trioxide thermal dissociation method, chemical reagent consumption, low cost, and the purity of WO₃ reached 99.995%-99.999%, reached the requirements of high pure tungsten trioxide.

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