Comment on “The stability of UO2OH+ and UO2(HPO4)22− complexes at 25°C” by G. Dongarra and D. Langmuir

Equilibrium calculations have shown that all the solutions in the experiments of Dongarra and Langmuir (1980) were super-saturated with respect to uranyl triphosphate; the degree of super-saturation varied from 3 to 857. In spite of the super-saturation, for all of their experiments n? and molal % UO₂(HPO⁴)₂^2? have been found to be <0.5 and <12 respectively. Similarly in all of their experiments 88–98% of ∑U(VI) existed as UO₂²⁺ or hydroxo complexes. Based on the analysis of their data it has been shown that their experimental conditions were not appropriate for determining the stability constant of UO₂(HPO⁴)₂^2?. The significance of careful design of experiments has been demonstrated. The uncertainty in log β (±0.2) as reported by these authors is too small in view of the very small $\text{n}\text{?}$ as well as negligible pH change during titrations. Furthermore, the fact that the β determined by Dongarra and Langmuir is very close to that of Moskvin et al. (1967) certainly does not serve to validate the work of Dongarra and Langmuir, since Dongarra and Langmuir, as well as this writer, have found several problems in the work of Moskvin et al.