Tungsten Trioxide Content Measurement
In the prior technology, gravimetric, volumetric, colorimetry, polarography and atomic absorption spectrometry method etc. are the main approaches to measure the content of tungsten trioxide in tungsten mine. In general, gravimetric and volumetric method are suitable for the high levels of tungsten content; and for the low level of tungsten content, colorimetry, polarography and atomic absorption spectrometry method are supposed to be better. In the following, we will describe the burning of ammonium tungstate gravimetric and thiocyanate photometric method.
Thiocyanate Photometric Method
A strengthening process of thiocyanate photometric method which shows as bellows:
1.Using a small amount of sample to be dissolved in the presence of ammonium fluoride, hydrochloric, nitric and perchloric acid, the tungsten precipitated in the form of tungstic acid, part of molybdenum precipitated in the form of molybdic acid;
2.Filtered to separate tungsten and molybdenum with the most coexistence elements, and then dissolved tungstate and molybdic acid with ammonia, the filtrate is evaporated to dryness, burning, and removing silicon by hydrofluoric acid, weighing the total weight of tungsten trioxide and molybdenum trioxide after burning;
3.Add sodium hydroxide to dissolve tungsten trioxide and molybdenum trioxide, and then measure the weight of molybdenum trioxide by thiocyanate photometric method;
4.Measure mass fraction of tungsten trioxide in residue and filtrate by thiocyanate photometric method to correct the result.
Burning of Ammonium Tungstate Gravimetric Method
Burning of ammonium tungstate gravimetric method is the common used method for the measurement of tungsten trioxide, which includes processes of selecting, pulverizing, weighting and dissolving and drying of the sample and the further steps, then taking tungsten trioxide as abscissa and absorbance as ordinate to draw curve and get tungsten trioxide content.
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