The Synthetic of Tungstic Acid:
Calcium Tungstate – hydrochloric acid decomposition method wolframite crushed and sodium hydroxide, generating sodium Tungstate solution by filtration, purification, and then with the calcium chloride solution metathesis reaction to obtain calcium Tungstate, and then hydrochloric acid, After washing the resulting Tungstic Acid, dried and pulverized to obtain Tungstic Acid product. Hydrochloric acid decomposition method wolframite after alkaline hydrolysis with sodium hydroxide, hydrochloric acid, ammonium chloride solution with filtered, washed through, get refined ammonium Tungstate solution, hydrochloric acid solution and then get Tungstate, and then by dehydration, drying, grinding, that was finished Tungstate.
Tungstate using hydrochloric acid decomposition. A saturated aqueous solution of Sodium Tungstate Na2WO4, calcium Tungstate CaWO4 like Tungstate heating, the solution was slowly added dropwise to a molar ratio of 2 to 3 times the amount of boiling concentrated hydrochloric acid. According to the above reaction precipitated yellow Tungstate. Then if dropping too fast or fluid temperature drops, it is easy to generate a suspension-like or colloidal precipitation, to further processing difficult. After dropping on a water bath heating was continued 1h, the precipitate becomes easy filtration, washed with 5% aqueous solution of ammonium nitrate was washed several times, will be completely removed upon standing Cl-. After filtration and dried at 120 ℃.
The Properties and Stability of Tungstic Acid:
If used and stored according to specifications will not decompose. Slightly soluble in water, soluble alkali, hydrofluoric acid and ammonia, almost insoluble in acid.
100 ℃ start dehydration, boiling point 1473 ℃. High temperature burning into Tungsten Trioxide. Insoluble in water and most acids, slightly soluble in water, soluble alkali, hydrofluoric acid and ammonia. N-Tungstic Acid or secondary Tungstate solution to dilute acid treatment available colloidal Tungstic Acid, containing different amounts of water, the water solubility and activity than the large yellow Tungstic Acid. Powdery white Tungstate activity compared with the big yellow Tungstate. Tungstate solution can be added to a solution of dilute nitric acid role in the system.
Yellow Tungstic Acid used in the manufacture of Tungsten metal powder, powdered white acid can be used to prepare the partial Tungstate and Tungsten-containing heteropolyacid salt.
niobiummetal 