99% sodium tungstate’s impurities may be determined using lanthanum hydroxide as coprecipitation agent by inductively coupled plasma atomic emission spectrometry (ICP-AES method) after coprecipitation separation and concentration of these impurities. These trace metal impurities are calcium, tin, cobalt, copper, iron, manganese, zinc, and nickel, etc.
The determination of trace metal impurities must be performed on a high resolution spectrometer if the ICP-AES method is adopted directly. That is because the matrix tungsten often has severe spectral overlap interference with the trace impurity elements being measured. So, chemical separation should be done before impurities determination if medium-resolution spectrometer is used for analysis.
And therefore, the metal impurity elements in sodium tungstate are usually undergoing predissociation and enrichment by the coprecipitation method. The lanthanum hydroxide is used as coprecipitant, which can absorb or entrap the elements existing in the form of cations in the solution, and is separated from the base tungstate after filtration. Lanthanum hydroxide is readily soluble in acid, and the spectrum of lanthanum is relatively simple so that it will not interfere with the measurement of impurity elements.
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