Acid extraction of radionuclides from soil samples using autoclave decomposition

Abstract

The specifics of the nuclear tests carried out on the territory of the former Semipalatinsk test site (STS) led to the emergence of various sites that differ in levels of radioactive contamination and radionuclide composition. This also led to a significant difference in the solubility of radioactive particles. Traditionally, the “Experimental Field” testing ground was characterized by the presence of sparingly soluble, vitrified particles, which was determined by the features inherent in ground tests of nuclear weapons, namely, the interaction of the high-temperature explosion region with soil particles. The presence of such sparingly soluble particles in the soil cover makes it impossible to use 6–8 М HCl and 7–8 М HNO 3 solutions which are most often used radiochemical analysis to determine the content of 90Sr and 239+240Pu. This paper considers methods for the acid extraction of anthropogenic radionuclides from soils of the STS using autoclaving. The aim of the research is to develop a method for the acid extraction of anthropogenic radionuclides from enlarged soil samples using autoclave decomposition. A blank soil sample was used to determine the optimal autoclave decomposition parameters; to test the acid extraction method, a soil sample was taken from the territory of the “experimental field” testing ground. The radionuclide 137Cs has been used as the most optimal indicator of acid extraction due to its strong fixation on clay and mineral soil particles and ease of detection by the gamma radiation. Autoclave decomposition has been carried out by dissolving the studied samples in a mixture of mineral acids (HCl, HNO3, HF, H2SO4). The specific activity of radionuclide has been determined on a BE3830 gamma spectrometer with a high-purity germanium detector (Canberra, USA), the amount of undecomposed soil residue has been determined gravimetrically (PA214C analytical balance, Ohaus, USA). The data obtained indicate that the most complete extraction of 137Cs occurs when using concentrated HF solutions (individually or in a mixture with other mineral acids). The degree of extraction of 137Cs varied from 85 to 100%. The worst results have been shown by the use of a mixture of acids 3HCl:HNO 3. In this case the degree of extraction of 137Cs did not exceed 20%. The efficiency of decomposition of soil samples weighing 10 g with a concentrated solution of HF at a temperature of 120 to 160 ºC was ≥95%.