Study on the Feasibility of Strontium Internal Standard Method in the Determination of Uranium in Natural Uranium Product (U₃O₈) by Solution Sampling-X-Ray Fluorescence Spectrometry

A method for the determination of uranium in natural uranium product (U₃O₈) was established by X-ray fluorescence spectrometry (XRFS) after preparation of sample with solution method. The feasibility of the strontium internal standard method was discussed from the aspects of strontium level in sample, the selection of strontium analytical spectral line, the selection of strontium internal standard compound, and the effect of sulfur content in sample on strontium. 0.600 00 g of dry internal standard strontium carbonate was mixed with 1.000 00 g of natural uranium product (U₃O₈), and the mixture was digested with phosphoric acid and nitric acid under the heat condition on an electric stove. The digestion solution (20 g) was taken into a plastic sample cup, and determined under the optimized working conditions of XRFS instrument. Standard solution series prepared by standard material GBW 04205 were used to make standard curve, and parameters of which were introduced to establish the correction formula to eliminate matrix effect. The results showed that mass fraction of strontium in sample was not more than 8.0 μg·g^-1 when mass fraction of sulfur was less than 2.00%, which did not affect the determination of uranium by strontium internal standard method; when the amount of internal standard strontium carbonate was 0.600 00 g and the K_α of strontium was used as an internal standard characteristic line, the fluorescence intensity and absorption-enhancement effect of strontium and uranium were basically the same, and the determination of uranium was not affected by the constant volume of sample solution, injection volume and instrument fluctuation. Linear range of uranium of standard curve was found in the range of 78.78%-87.25%. The standard material GBW 04205 was analyzed 11 times in parallel, RSD of the determined values was 0.061%, and the absolute difference between the determined value (84.722%) and the certified value (84.711%) was 0.011%, which was less than quality control index (0.1%) of uranium in the trade detection of natural uranium product (U₃O₈). The proposed method was applied to the analysis of six actual samples, with determined values basically consistent with those obtained by potentiometric titration of national standard GB/T 11848.1-1989.