Study on Properties of TBP‐HNO₃ Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO₂

The tri‐ n ‐butyl phosphate‐nitric acid (TBP‐HNO 3 ) complex prepared by contacting the pure TBP with the concentrated HNO 3 can be used for direct dissolution of lanthanide and actinide oxides in the supercritical fluid carbon dioxide (SCF‐CO 2 ). Properties of the TBP‐HNO 3 complex have been studied. Experimental results showed that when the initial HNO 3 /TBP volume ratio was varied from 1:7 to 5:1, the concentration of HNO 3 in the TBP‐HNO 3 complex changed from 1.95 to 5.89 mol/L, the [HNO 3 ]/[TBP] ratio of the TBP‐HNO 3 complex changed from 0.61 to 2.22, and the content of H 2 O in the TBP‐HNO 3 complex changed from 2.02% to 4.19%. All of the density, viscosity and surface tension of the TBP‐HNO 3 complex changed with the concentration of HNO 3 in the complex, and were higher than those of the pure TBP. The protons of HNO 3 and H 2 O in the complex underwent rapid exchange to exhibit a singlet resonance peak in nuclear magnetic resonance spectra. When the TBP‐HNO 3 complex was dissolved in a low dielectric constant solvent, small droplets of HNO 3 were formed that can be detected by NMR.