Determination of divalent iron content in reference materials of rocks and soils by X-ray fluorescence analysis

The potential of the X-ray fluorescence method as a tool for assessing the ratio of valence forms of iron in reference materials of soils, igneous and sedimentary rocks for the purpose of their characterization is described. The method is based on the dependence of the ratio of intensities of FeKβ5 and FeKβ1,3 emission lines on iron valent state. The study was carried out using a wavelength-dispersive X-ray fluorescence spectrometer. Forty-four reference materials of igneous and sedimentary rocks produced in Russia and Mongolia were used as calibration set. The content of total and divalent iron (present as FeO oxide) in these samples was certified, with the fraction of divalent iron from 2 to 92 % in the total iron content. Fourteen reference materials with unknown FeO content were analyzed by proposed X-ray fluorescence technique. The obtained data showed satisfactory agreement with the results of analysis by the reference dichromate titration technique (NSAM No. 50-X). In addition, 6 reference materials with approximate values of FeO content were analyzed. The results obtained by the X-ray fluorescence technique showed satisfactory agreement with the estimate data. For 20 reference materials with FeO content from 0.23 to 8.8 %, the standard deviation in determination by the X-ray fluorescence method was 0.30 %. The information on FeO content in the reference samples of soils, igneous and sedimentary rocks obtained for the first time can be used in the analytical practice and be useful for geologists.