Uranium release from a natural rock under near-natural oxidizing conditions

Abstract

Understanding how uranium (U) moves through the soil and groundwater is essential to determine the effectiveness of cleanup technologies. Uranium release and transport in the subsurface under oxic conditions have been reported to be mostly dependent on sorption onto Fe/Mn-oxide and complex interactions with organic substances. Available information in the literature however presents evidence of U retardation by natural sands. The aim of this investigation was to characterize U dissolution from a uraninite-containing rock (UO2-rock) in different waters under test conditions relevant to U transport from mine wastes (tailings). For this purpose, not shaken batch experiments were conducted with a constant amount of an UO2-rock and different types of water (deionised, tap and mineral water). For comparison parallel experiments were conducted with 0.1 M Na2CO3 and 0.1 M H2SO4. Further dissolution experiments using UO2-rock together with dolomite and pyrite were conducted. The results indicate that carbonate addition (soluble or in-situ generated) enhanced U solubilization, whereas pyrite addition essentially slowed the initial U solubilization. It is shown that SiO2 and other rock constituents may contribute to retard U transport.