Ammonium Tungstate Produced by Extraction Method
Extraction is one of the main methods for producing ammonium tungstate at present, besides that, there is also neutralization method, evaporation method and ion exchange method, among which evaporation method is the mostly applied.
Extraction is the use of a solute in a solvent immiscible in different solubility, extraction with a solvent of the solute from the solvent, the other consisting of a solution coming out.
Extraction Method Steps
1.Pretreatment. Firstly add in NaOH solution to alkali decomposite and digest of tungsten concentrate, the produced coarse sodium tungstate solution after filtering it sent to be purified, tungsten residue is cleaned after soft water and kept in slag deposal pit temporarily.
2.Purification. Coarse sodium tungstate solution contains impurities like silicon, arsenic, phosphorus, molybdenum. Add dilute sulfuric acid to adjust pH value, then add magnesium sulfur to purify and precipitate the impurities as magnesium salt. Purified solution after being filtered then turns into fine sodium tungstate solution, add into agitator bath with sodium sulphur, molybdenum trisulfide is obtained, after filtration, pure sodium tungstate is obtained.
3.Extraction. Add sulfuric acid into pure sodium tungstate solution and adjust pH value to 2~3, sodium tungstate will aggregate into sodium metatungstate, add in gas and other organic phase to extract, tungsten will form as extract complex and enters into organic phase. By washing with water, add in ammonia solution and by extraction, ammonium tungstate solution is obtained.
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