Industrially, the raw material mineral wolframite is extracted with sodium hydroxide aqueous solution to make crude sodium tungstate, and then the crude product is made into WO3?2H2O with acid, sodium hydroxide is used to make Na2WO4?2H2O. It should be noted that WO3?2H2O is difficult to completely convert into Na2WO4?2H2O. How to determine the content of tungsten trioxide in sodium tungstate?
The content of tungsten trioxide in sodium tungstate is generally determined by the cinchonine gravimetric method. Below, let's take a look at some basic information about the cinchonine weight method.
- Method summary: In a hot solution with a pH value of 3.00～4.4, cinchonine hydrochloride is used to precipitate tungstic acid and separate from impurities. After burning, it becomes tungsten trioxide, which is weighed and colorimetric.
- Reagents: methyl violet indicator 0.1%, hydrochloric acid (1+1), cinchonine hydrochloric acid solution 10% (prepared with 1+1 hydrochloric acid), cinchonine hydrochloric acid lotion 0.2%, solid NaOH, extensive test paper.
- Operation steps: Weigh 0.5 g of the sample in a 250ml beaker, dissolve it with a little water, add 100ml of hot water at 60～80°C, 2 drops of 0.1% methyl orange finger agent, and neutralize with hydrochloric acid (1+1) to red, add 10ml of 10% cinchonine under constant stirring, continue to stir to make the precipitation coagulate, the supernatant liquid is clearer and stand still, after the precipitation sinks, filter with fast quantitative filter paper, the filtrate is taken in a 250ml volumetric flask, used for precipitation Wash with 0.2% cinchonine lotion for more than five times. After washing, the precipitate is transferred into a porcelain crucible together with filter paper, dried and carbonized in an electric furnace, and then carbonized and burned in a muffle furnace at 750-800°C for 30-45 minutes, cooled, and weighed. weight. The filtrate was carried out by tannin and methyl violet colorimetry.
- Calculation of analysis results: WO3(%)=(W/G)×100+C. In the formula: W——Weight of tungsten trioxide (g), G——Weight of sample (g), C——WO3 content measured in the filtrate.
- Matters needing attention:
①The precipitate must be washed with sodium ions, otherwise the burnt material will turn black and the result will be high.
②The indicator can be 0.1% methyl orange, then the filtrate can be carried out according to the thiocyanate colorimetric method.
