Ammonium metatungstate is a colorless crystalline polytungstic acid, the molecular formula is H6[H2(W3O10)4]•nH2O (n is 10 or 23), the density is about 3.93g/cm3, it is easily soluble in water and easy to degrade. The thermal stability is poor, so there are great difficulties in preparation. There are two common traditional preparation methods:
Method 1: Add the cationic resin to the continuously stirring 80°C sodium tungstate solution with a concentration of 2% until the pH value of the solution is 2.5. After continuing to stir for 20 minutes, put the solution in a water bath for 2 hours, and then use chlorination Barium solution treatment, the slightly soluble part is filtered out to obtain the barium metatungstate filtrate, and then the barium metatungstate filtrate is recrystallized several times, and finally the solution is made again, the solution is exchanged by cationic resin, and the exchange liquid is heated in hot air evaporated to obtain metatungstic acid crystals.
Method 2: Acidify the tungstate solution to a pH value of about 4.0, then maintain the pH value of the solution, age for 48 hours, add an appropriate amount of ether-12N sulfuric acid, and generate an oily metatungstate ether with a large specific gravity after shaking, and then The oil is rapidly dried to obtain crystalline metatungstic acid.
The above two methods have problems such as complex process, high production cost, low production capacity, poor product quality and large environmental pollution to varying degrees. For this reason, the researcher of patent No. CN1066418C has developed a kind of technology relatively simple, and cost is low, and environmental pollution is little, is conducive to the preparation method of industrialized production H6 (H2W12O40). Use ammonium paratungstate powder to dissociate at a temperature of 270°C to 350°C to generate ammonium metatungstate. The dissociation time is 30-60 minutes. Then add deionized water to the obtained ammonium metatungstate powder for leaching and stirring to obtain an emulsion , filter out the insoluble matter, age the filtrate in a water bath at 60-90° C. for 4-24 hours, then filter again, and exchange the filtrate with a cation resin to obtain a H6 (H2W12O40) solution.
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