Solubility Studies of the Lead Uranyl Oxyhydrate Mineral Curite

In this thesis, Curite is a lead uranyl oxyhydrate mineral [Pb3(UO2)8O8(OH)6(H2O)2] that forms due to oxidative alteration of uraninite in geologically old uranium deposits. Curite is a member of the uranyl oxyhydrate mineral family and these in general impact uranium release and transport in the environment (Plasil, 2014). Curite is one of several Pb uranyl oxyhydrate minerals that form during the initial stages of alteration of uraninite that contains radiogenic lead (Plasil, 2014). Little is known about the thermodynamics of most of these uranyl phases whose solubility may impact the mobility and ultimate distribution of U. The only thermodynamic data that is available for this group of minerals is for curite for which the enthalpy of formation was determined using high-temperature oxide melt solution calorimetry (Kubatko et al., 2005). In this project, solubility experiments using synthetic curite were conducted from undersaturation and supersaturation to obtain the equilibrium state. Using the solubility data, the logKsp was calculated to be 32.685±0.570 at pH 2.8, 41.413±0.752 at pH 3.3 and 45.152±0.948 at pH 3.8, respectively in undersaturated experiments. In supersaturated experiments, the logKsp was calculated to be 36.4±0.6 at pH 2.8, 44.0±0.5 at pH 3.3 and 50.2±0.8 at pH 3.8.