Grade 1 tungsten trioxide is referred to as a light yellow crystalline powder with grade of WO3-1.
Processes of Double Salt Method to Produce Tungsten Trioxide
1. By using sodium hydroxide to decompose tungsten concentrate to obtain crude sodium tungstate solution.
2. By adopting an improved "Chemical Purification Method" to remove silicon (Si), phosphorus (P), arsenic (As), fluorine (F), molybdenum (Mo) and other major impurities in the obtained solution.
3. Ammonium chloride is added to form "ammonium paratungstate - sodium complex salt". And the complex salt is separated to get purer complex salt.
4. The obtained complex salt is treated by one of the following two kinds of methods to obtain tungsten trioxide.
(1) The complex salt is decomposed with hydrochloric acid (HCL) to obtain tungstic acid. Then, the tungstic acid is washed, dried and calcined to obtain tungsten trioxide.
(2) The complex salt is treated (converted) with saturated ammonium chloride solution again to obtain ammonium paratungstate (APT). After drying, APT is directly calcined to obtain tungsten trioxide.
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