Solid-liquid Phase Equilibria of U(VI) in NaCl Solutions

Solubility of Nd3+ and UO22+ in WIPP brine as oxidation-state invariant analogs for plutonium

“…Under these conditions a small uptake of CO 2 was possible during the time of sampling when the experiment container was open for a short time. This small change in protocol led to uranium concentrations that were up to two orders of magnitude higher than in our nitrogencontrolled atmosphere experiments, and were comparable to those reported by Diaz and Grambow [5] who reported a uranium solubility of (2.8 ± 1.8) × 10 −5 M at pC H+ = 8.9 in 5 M sodium chloride with a similar experimental approach using only argon bubbling to remove carbonate. In contrast to this, the solubility of uranium in our carbon dioxide-free ERDA-6 brine was (2.0 ± 1.7) × 10 −7 M. We believe that the lower uranium concentrations we report reflects the better efficiency we had in removing carbonate from the brine solutions at the beginning of the experiments, as well as better controls to maintain a carbon dioxide-free environment throughout our experiments.…”

Coprecipitation of Mono-, Di-, Tri-, Tetra- and Hexavalent Ions with Na-Polyuranates

“…Together with the results from solid state analyses described above, we can conclude that the same Na-polyuranate phase has been formed in the systems A and C as reported for the pure NaCl-U(VI)-H 2 0 system, i.e. a Na-polyuranate with a Na/U ratio of about 0.3 [5] with a similar dependence of crystallinity in all systems.…”

“…In order to compare whether the precipitation process of the Na-polyuranate was similar in all tests, Figure 4 shows the time dependency of U(VI) concentration (0.2 and 0.45 pm filtered) at pH = 5.5-5.7 in three different systems: NaCl-U(VI)-H 2 0 [5,12]; systems A and C. The data of all systems show very good agreement, indicating that the precipitation method yields highly reproducible results and the presence of minor elements in solution did neither influence the precipitation kinetics nor the final U(VI) concentration. Together with the results from solid state analyses described above, we can conclude that the same Na-polyuranate phase has been formed in the systems A and C as reported for the pure NaCl-U(VI)-H 2 0 system, i.e.…”

“…Solid phase samples were prepared from aliquots of an aqueous suspension of the precipitate in its mother liquid as described by Diaz and Grambow [5]. The chemical composition of the solid phases was analysed after dissolution in 1% HN0 3 pH correct = pH meas + 0.25.…”

“…It has been shown that Na-polyuranates are the principal stable solid phases of U(VI), in NaCl solutions [5]. These phases can easily form solid solutions.…”