Mineral-solution interactions in the U(VI)-CO2-H2O system

Interactions between U(VI) and calcite appear to be limited to adsorption reactions at the surface. U(VI) is concentrated at the calcite solution-interface at slightly alkaline pH. However, its mobility is dependent on solution pH. The interactions at the mineral-solution interface may be modeled thermodynamically in terms of the concentration of U(VI) adsorbed at the carbonate surface and the activity of the calcite component: UO22++CaCO3(s)=>UO2CO3+Ca2+ where the > symbol denotes a surface species. The equilibrium constant, KU(VI),calcite=105.12 and is independent of solution pH. (orig.)