The effect of moisture on the desorption behavior of UF6 from NaF adsorbent

Study on the Thermal Stability of the Na2UF8 Complex in the Argon Atmosphere

“…As shown in Figure a, there existed several peaks locating at 170, 286, 306, 345, 375, 411, and 609 cm –1 at room temperature, which was consistent with our previous work . The characteristic vibrational frequency at 609 cm –1 was assigned to the symmetric stretching vibration of the U–F bond of Na 2 UF 8 , and it slightly red-shifted with the increase of the temperature (as shown in Table ).…”

“…This reversible reaction between UF 6 and NaF is of great significance for the separation of the volatile impurities from the UF 6 product. − Our previous study indicated that Na 2 UF 8 was stable in anhydrous environment, and the obvious desorption of UF 6 from NaF sorbent occurred when the temperature exceeded 200 °C with a maximal desorption rate of UF 6 at 330 °C. We also found that the desorption behavior of UF 6 from the NaF sorbent in the fluorine atmosphere was similar to that in the argon atmosphere, while the amount of the uranium residue on the NaF sorbent after desorption in the argon atmosphere (1.68 mg U/g NaF) was significantly larger than that in the F 2 atmosphere (0.006 mg U/g NaF) . Cathers et al speculated that the uranium residue on the NaF sorbent was the nonvolatile NaF–UF 5 complex when the Na 2 UF 8 complex was heated to 200–450 °C in nitrogen, and the NaF–UF 5 complex was further converted into the NaF–UF 4 complex when the temperature was above 450 °C.…”

“…As shown in Figure 1a, there existed several peaks locating at 170, 286, 306, 345, 375, 411, and 609 cm −1 at room temperature, which was consistent with our previous work. 9 The characteristic vibrational frequency at 609 cm −1 was assigned to the symmetric stretching vibration of the U−F bond of Na 2 UF 8 , and it slightly red-shifted with the increase of the temperature (as shown in Table 1). At the same time, the peaks below 500 cm −1 gradually widened apparently, which was because of the increase of the U−F bond length and the amplitude of the corresponding stretching vibration.…”

“…The complex layer became thin and sparse due to the release of UF 6 when the temperature was 300 °C (Figure 2c,d). Compared to the blank NaF sorbent, 9 the surface of NaF crystalline grains became rough and uneven at 350 °C (Figure 2e,f), and the Na 2 UF 8 complex completely disappeared. From the abovementioned results, it can be confirmed that Na 2 UF 8 is relatively stable in the argon atmosphere below 300 °C; most Na 2 UF 8 were decomposed into NaF and UF 6 when the temperature was above 320 °C; meanwhile, a small amount of Na 2 UF 8 might transform into a new compound.…”

“…We also found that the desorption behavior of UF 6 from the NaF sorbent in the fluorine atmosphere was similar to that in the argon atmosphere, while the amount of the uranium residue on the NaF sorbent after desorption in the argon atmosphere (1.68 mg U/g NaF) was significantly larger than that in the F 2 atmosphere (0.006 mg U/g NaF). 9 Cathers et al 10 speculated that the uranium residue on the NaF sorbent was the nonvolatile NaF−UF 5 complex when the Na 2 UF 8 complex was heated to 200−450 °C in nitrogen, and the NaF−UF 5 complex was further converted into the NaF−UF 4 complex when the temperature was above 450 °C. By dissolving and analyzing the spent NaF from sorption columns of Chemical Combine, Gromov et al 11 the inert atmosphere would lead to the formation of the uranium residue on the NaF sorbent, and the temperature also had an important influence on the chemical form of the uranium residue.…”