Solubility and Complexation of the Bismuthate Ion in Nitric Acid Systems
Here, the dissolution rate and solubility of NaBiO 3 have been investigated in nitric acid systems ranging from 4–6 M HNO 3 , and were found to be 58–76 µg/cm 2 ·d and 490–830 mM, respectively. The presence of 50 mM U(VI) drastically increased the solubility to 540–1200 mM, while rates of dissolu-tion were relatively unchanged. The solubility of NaBiO 3 increased with an increase in U(VI) con-centrations at 4 M HNO 3 , with log-log analysis indicating a one-to-one complex between Bi and U and IR spectroscopic evidence monitoring uranyl stretching suggesting complex formation. Absorb-ance spectra were obtained experimentally and computationally with an absorbance band in the range of 450–600 nm that has been attributed to Bi(V). The ingrowth and decay of Bi(V) in solution was also studied as a function of mass of solid NaBiO 3 present, acidity, and temperature. The ac-tivation energies of dissolution and decomposition were calculated to be 39 ± 4 and 61 ± 6 kJ/mol, re-spectively. Furthermore, these results indicate that dissolution of NaBiO 3 into the respective Na + and BiO 3 – is occur-ring prior to undergoing reduction, a process which conventionally has been believed to occur in the reverse order.