Determination of Wolfram in Tungsten Ore by Pressurized Acid Digestion-Inductively Coupled Plasma-Atomic Emission Spectrometry

Tungsten is prone to hydrolysis of hydrated tungsten oxide in acidic medium, so it is usually measured using traditional methods of weight method and spectrophotometry after alkaline fusion, which needs complex operation and large sampling size (0.1-0.5 g). A new method of analysis of tungsten ores has been established by using pressurized acid digestion and a hydrofluoric acid system for Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and is described in this paper. Tungsten ores were effectively decomposed at 170℃ for 20 h, and then the samples were quickly dissolved in mixed acids of 5% hydrofluoric acid and 10% nitric acid. Tungsten in the form of the stable eutectic hexavalent complexes was determined by ICP-AES with a hydrofluoric acid resistant device. The detection limits of this method are 0.039-0.042 μg/g. Both the accuracy and precision of the method were validated by analyzing standard reference materials GBW 07240, GBW 07241, with 1.53%-6.42% (RSD, n=10). The results were in good agreement with the certified values of the national standard materials. This method can effectively solve the problems of tungsten hydrolysis easily in acidic medium. The operation is simple and has a relatively short digestion time of 20 h. The method can be used to analyze tungsten content in the range of 0.015%-50%.