Journal of Nuclear Fuel Cycle and Waste Technology

Uranium (U), an essential source for nuclear energy production, poses serious environmental and radiological threat due to its high mobility and long half-life. Uranophane [Ca(UO₂)₂SiO₃(OH)₂·5H₂O], a secondary U silicate mineral, is known as a solubility-limiting phase in U mining deposits and nuclear waste repositories (controlling U immobilization). However, research on uranophane dissolution, particularly under the influence of organic and inorganic ligands, remains lacking. This study investigates uranophane synthesis and its dissolution at pH 8 through batch experiments using organic ligands (citric acid (CA) and humic acid (HA) at 50–150 ppm) and inorganic ligands (carbonate, nitrate, chloride, and silicate at 10−⁴ M to 10−⁶ M). Obtained results suggested that CA and carbonate significantly enhanced U release, reaching 27.6 ppm. Mixed systems containing both organic (50–150 ppm CA) and inorganic (10−⁴ M carbonate) ligands revealed increased U release, however were less effective than single-ligand systems due to competitive interactions with carbonate dominating U speciation. Visual MINTEQ modeling was used to identify uranyl complex species in the solutions. Dissolution rate and kinetic modeling were determined to predict U release trends. These findings emphasize the role of various ligand types in nature and their impact on U mobility, aiding remediation strategies for contaminated environments.

Keywords

Uranium, Uranyl silicate minerals, Uranophane, Inorganic ligands, Organic ligands, Dissolution