Determining Fluoride Content in Sodium Diuranate Using Microwave Extraction-Ion Chromatography

Sodium diuranate, commonly known as “yellow cake”, is an important raw material for nuclear fuel in the nuclear industry. There are also clear requirements for the technical conditions of sodium diuranate, in which the content of F(dry basis) should be controlled below 0.2%. At present, the ion-selective electrode method is used to analyze the content of F in sodium diuranate. When the method is used for measurement, a plurality of reagents such as nitric acid, sodium hydroxide, hydrogen peroxide and sodium citrate are heated and dissolved in the sample dissolution preparation process. In the process of sample analysis, the measurement of fluoride ion electrode is vulnerable to environmental temperature and humidity changes and fluoride ion pollution, which affect the accuracy of the measurement potential results. Microwave extraction technology is a method to use microwave radiation to accelerate the extraction of compounds from samples, which can extract target compounds efficiently and quickly, and reduce the impact on the environment. Sample preparation objects include organic matter, inorganic anions, etc., and have been applied to soil samples, plant samples and solid samples. Ion chromatography is commonly used for the analysis of inorganic anions. This method is based on the different partition coefficients of different substances between the mobile phase(solvent) and the stationary phase(column packing), and is a technique for the separation and quantitative analysis of ions in solutions. A rapid and accurate method for the determination of fluorine in sodium diuranate was established by microwave extraction and ion chromatography. The sample mass of sodium diuranate is 0.0100-0.1000 g, 15 mL of 0. 01 mol/L HNO₃ extractant solution is added, the extraction power percentage is controlled at 80% with extraction time of 10 min. The extraction solution was filtered by using a Na-type ion chromatography sample pretreatment column and a 0.22 μm filter. The filtrate sample was pumped into the ion chromatograph for analysis with 15 mmol/L sodium hydroxide as the eluent. The method has a detection limit of 0. 000025%, a low determination limit of 0.0001%, and a measurement range of 0.0001%-0.5000% for that determination of fluorine content in the diuranate, and meets the monitor and measurement requirements of the diuranate technical condition index control standard that the fluorine content is less than 0.2%. Compared with the ion-selective electrode method, the developed method has the advantages of simple operation, convenient sample preparation, wider measurement range, less sample consumption and the like, and is suitable for the accurate and rapid analysis of F in sodium diuranate.