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.
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