Determination of Ammonium Paratungstate Impurities

Ammonium paratungstate is a chemical substance that is mainly white crystalline with two types of flaky crystals and needle-like crystals. It is used to produce tungsten trioxide made of tungsten trioxide or blue tungsten oxide. It is also used to produce ammonium metatungstate and other tungsten compounds. The impurities in ammonium paratungstate have a great influence on its quality. 

At present, the detection method of impurities in ammonium paratungstate is mainly based on colorimetry, and the subsequent improved detection methods are atomic absorption spectrometry and ICP detection.

Although the ICP detection method improves the sensitivity of the test, it has a higher requirement for the equipment, and it needs to increase the device of HF resistance. In the detection process for tungsten interference, often take the matrix matching method for detection, however, due to the impurity content in ammonium paratungstate is low, the matrix matching method in interference matrix on the impurity is too big, not easy to detect the content of impurities, so before the usual ICG method, also need to do pre treatment.

A.The ammonium paratungstate sample is placed in a muffle furnace and heated to above 500 ℃. and incubated for 20 minutes. The ammonium paratungstate is calcined to tungsten trioxide.

B.After adding the hydrogen peroxide solution to the cooled sample, it was placed in a 300-mL Erlenmeyer flask, placed in an electric furnace and heated to 120 ℃. to completely dissolve, and the burned tungsten trioxide was dissolved in hydrogen peroxide solution.

C.Concentrated nitric acid was added to the sample to form tungsten tungstic acid and then filtered with filter paper. Since the heated ammonium paratungstate sample was added with hydrogen peroxide solution and placed in a 300-mL Erlenmeyer flask, the temperature of this step was 120°C-150°C. In this process, acid mist will condense on the wall of the conical flask. During this process, the conical flask is washed 3 times with water, the acid mist on the wall is flushed into the bottle, and the water is boiled until it dries.

D.After determining the volume of the filtrate, use ICP detection.

Through the precursor treatment of the ammonium paratungstate sample, the flocculated tungstic acid precipitates in the process, which can avoid the interference of tungsten caused by tungstic acid into the filtrate due to too small acidity during filtration and washing. At the same time, due to the formation of large particles of precipitates, the adsorption of impurity ions by tungstate precipitation is reduced during the washing process, which improves the accuracy of IGP. It can detect 13 impurity elements at the same time, and the recovery effect is good, and the obtained test data are accurate.

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