There are multiple preparation methods of phosphotungstic acid, mainly including:
(1) It is obtained by acidifying sodium tungstate solution with phosphoric acid and hydrochloric acid, and then extracting it with ether.
Phosphotungstic acid is easily prepared by the method of Rosenheim and Jaenicke. Dissolve 1000g sodium tungstate (Na2WO4•2H2O) and 160g disodium hydrogen phosphate (Na2HPO4•2H2O) in 1500mL boiling water. 800 mL of concentrated hydrochloric acid was added dropwise thereto under constant stirring. Phosphotungstic acid began to separate out when half of the acid was added. Since the precipitated acid must be purified, it is not necessary to filter it. After the solution was cooled, diethyl ether without reducing agent was added until the mixture separated into three liquid layers after shaking. This requires approximately 600 mL of ether. If necessary, add some water to dissolve the sodium chloride. The bottom liquid layer is phosphotungstic acid-ether complex, add water to wash several times, and add enough ether each time to form the third liquid layer. Then pass the washed and dust-free air into the ether layer to make it evaporate and crystallize. After filtering, keep the crystals open in the air, but keep them away from dust until they no longer have the smell of ether, and the yield is about 80% based on sodium tungstate.
(2) A method for preparing high-purity phosphotungstic acid from sodium tungstate, comprising the following steps: (1) contacting sodium tungstate solution with inorganic acid solution until active tungstic acid precipitates are formed. (2) Contact the active tungstic acid precipitate with phosphoric acid solution until the active tungstic acid precipitate is completely dissolved to obtain a phosphotungstic acid solution. (3) Add inorganic acid precipitant to phosphotungstic acid solution to precipitate phosphotungstic acid, filter and crystallize to obtain high-purity phosphotungstic acid.
Upstream raw materials for the preparation of phosphotungstic acid: phosphoric acid, tungsten trioxide, caustic soda, hydrochloric acid, ether.
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