Measurement of Re in Soil by High Temperature Oxidation-ICP-MS

The dust and soil contaminated during the decommissioning process of nuclear facilities need to be sorted into radioactive waste and sent to the disposal site for disposal. According to the document requirements of “Radioactive Waste Classification”, technetium(Tc), as one of the important radionuclides in nuclear waste management, needs to accurately measure its radioactive activity concentration. The analysis process of ⁹⁹Tc in dust and soil mainly includes four processes: sample pretreatment, chemical separation and purification, source preparation and measurement. At present, technetium is extracted from the sample matrix by leaching method, total dissolution method or alkali fusion method, and then one or more methods are combined by co-precipitation method, solvent extraction, ion exchange, extraction chromatography and other separation methods for purification, removal of interfering components, and finally determination by liquid scintillation counting or mass spectrometry. The whole pre-processing process is tedious and takes several hours to several days, which takes a long time. Due to the high temperature volatilization of technetium oxide(Tc₂O₇), the high temperature volatilization method can be used to extract technetium from dust and soil samples, effectively remove the matrix and non-volatile interference substances, and obtain a simpler solution composition, making the subsequent purification steps simpler. In terms of measurement, the beta counting method uses the radioactivity of ⁹⁹Tc(T_1/2=2.1×10⁵ a). Although the source is simple and easy to use, due to the long half-life of ⁹⁹Tc, it is necessary to measure large samples for a long time to meet the detection requirements when analyzing low-level samples. Inductively coupled plasma mass spectrometry(ICP-MS) is widely used in the analysis of long-lived radionuclides because of its fast analysis speed, high sensitivity and low detection limit. Rhenium(Re) and technetium(Tc) are members of the ⅦB group and have similarities in electron layer structure, atomic radius, solubility, thermal stability and volatility. A high temperature oxidation inductively coupled plasma mass spectrometry(ICP-MS) method was developed for the determination of rhenium in soil by replacing technetium with rhenium. The results show that when the high temperature oxidation temperature is 1100 ℃, the flow rate of argon and oxygen is 200 mL/min, the high temperature oxidation time is 15 min, the simulated soil sample is treated with 10 mL 1.0 mol/L Na₂CO₃ solution as the absorption solution, and the ICP-MS measurement is carried out. The recovery of rhenium in soil is 89%-99%, and the relative standard deviation of the method is 4.5%(n=6)(rhenium mass concentration is 10 μg/g). It provides a method basis and separation scheme for the determination of ⁹⁹Tc in the dust of decommissioning facilities.