AUTHOR=Grambow B. , Müller R. , Schild D. , Gaona X. 

TITLE=Solids, colloids, and the hydrolysis of tetravalent uranium in chloride media

JOURNAL=Frontiers in Nuclear Engineering

VOLUME=2

YEAR=2023

URL=https://www.frontiersin.org/journals/nuclear-engineering/articles/10.3389/fnuen.2023.1308064

DOI=10.3389/fnuen.2023.1308064

ISSN=2813-3412

ABSTRACT=<p>Understanding of the properties of dissolution and precipitation of Uranium under reducing geochemical conditions is important in radioactive waste management and assessments of natural uranium deposits. The mechanism of forming UO<sub>2+y</sub> from U(VI) and U(IV) containing aqueous solution (1 M NaCl) and the solubilities of the precipitates were studied under well-controlled reducing conditions as a function of pH, particle size, and supersaturation. The results show that tetramer and colloid formation are critical initial steps. Precipitation is not growth-controlled but appears to be nucleation-controlled, with critical nuclei dimensions of one unit cell of UO<sub>2</sub>. The precipitates were always crystalline, and amorphous UO<sub>2</sub> was not observed.</p>