Closed vessels microwave digestion method for uranium analysis of soils using alpha-spectroscopy

Abstract

This paper describes our development of an accurate determination of uranium by alpha spectrometry using various kinds of sample digestion methods. The sample preparation techniques employed an acid digestion with HNO₃, and microwave oven digestion either by HNO₃ or by combination of HNO₃ and HF. The samples were obtained from surface and in depth(40 cm) soils from residential area. An extraction chromatography column has been used to separate the uranium from interference matrix and elements. Results show that the microwave method significantly speeds up the analysis time, reduces the volume of acids used and eliminates a large fraction of acid vapour emission. Compared with the uranium recoveries it was shown that microwave HNO₃+HF achieved greater recovery (83%) than microwave HNO₃ (78%), while less obtained by HNO₃ digestion using hot plate (75%). Various kind of digestion methods have been applied (24 times) for two kind of soil sample. The reproducibility was acceptable and the average precision (coefficient of variation) was between 4 to 5. No significant differences between the precision of the methods have been observed. Acid volume required for the microwave procedures are a fraction of 5 times lower and the analysis time 6 times lower than traditional digestion by hot plate technique.