The general formula of tungstic acid is mWO3•nH2O, which is a polymer compound formed by combining tungsten trioxide WO3 with water in different ratios and in different combinations. Yellow tungstic acid, white tungstic acid and metatungstic acid are known. Yellow tungstic acid: a common tungstic acid. Pale orange-yellow powder. The composition varies slightly with different preparation conditions. When the composition is exactly WO3•H2O, the chemical formula is H2WO4, the molecular weight is 249.86, the relative density is 5.5, and the refractive index is 2.24. When heated to 100°C, it dehydrates to generate WO3. Insoluble in water, it will gradually gel after soaking in water, soluble in ammonia water, alkali solution and concentrated hydrochloric acid. White tungstic acid: chemical general formula mWO3·nH2O, n: m>1.3, the ratio of n to m varies with the preparation conditions and drying conditions. Microcrystalline white powder. It has strong chemical activity, slightly photosensitivity, and is easy to restore. Tungstic acid belongs to inorganic metal compounds and is a widely used chemical raw material.
Mainly used in the production of metal tungsten, tungsten wire, tungstate, hard alloy, etc. Also used as petrochemical catalyst, printing and dyeing auxiliaries and lubricants. Tungstic acid is an important industrial product, mainly used as a catalyst. Its application examples are as follows:
1) The method of synthesizing bismuth tungstate with tungstic acid as tungsten source, dissolving tungstic acid in a mixed solution of hydrogen peroxide and deionized water to obtain a tungstic acid solution, and putting the obtained tungstic acid solution and bismuth nitrate into a container filled with deionized water In the hydrothermal reaction kettle, keep at 220°C for 24 hours, cool down to room temperature naturally, wash the obtained solid with distilled water, put it in an oven at 80°C for drying, and finally get powdered bismuth tungstate. The invention uses tungstic acid as a tungsten source and adopts a solution-based hydrothermal method for synthesis, and its preparation method is mild and can be used for large-scale production.
2) Preparation of high-purity phosphotungstic acid, including the following steps:
(1) Contact the sodium tungstate solution with the inorganic acid solution until active tungstic acid precipitates are formed.
(2) The active tungstic acid precipitate is contacted with the phosphoric acid solution until the active tungstic acid precipitate is completely dissolved to obtain a phosphotungstic acid solution.
(3) Add an inorganic acid precipitant to the phosphotungstic acid solution to precipitate the phosphotungstic acid, filter and crystallize to obtain high-purity phosphotungstic acid, and the molar concentration of the inorganic acid precipitant in the reaction system is 0.1~6mol/l. Compared with the prior art, the process is simple, the production process does not use a large amount of high-concentration strong acid and flammable organic extractant, the product has low phosphate content, and is suitable for use as an acid catalyst.
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