TY - JOUR
T1 - Effect of co-solutes on the products and solubility of uranium(VI) precipitated with phosphate
AU - Mehta, Vrajesh S.
AU - Maillot, Fabien
AU - Wang, Zheming
AU - Catalano, Jeffrey G.
AU - Giammar, Daniel E.
PY - 2014/1/22
Y1 - 2014/1/22
N2 - Uranyl phosphate solids are often found with uranium ores, and their low solubility makes them promising target phases for in situ remediation of uranium-contaminated subsurface environments. The products and solubility of uranium(VI) precipitated with phosphate can be affected by the pH, dissolved inorganic carbon (DIC) concentration, and co-solute composition (e.g. Na+/Ca2+) of the groundwater. Batch experiments were performed to study the effect of these parameters on the products and extent of uranium precipitation induced by phosphate addition. In the absence of co-solute cations, chernikovite [H3O(UO2)(PO4)·3H2O] precipitated despite uranyl orthophosphate [(UO2)3(PO4)2·4H2O] being thermodynamically more favorable under certain conditions. As determined using powder X-ray diffraction, electron microscopy, and laser induced fluorescence spectroscopy, the presence of Na+ or Ca2+ as a co-solute led to the precipitation of sodium autunite ([Na2(UO2)2(PO4)2] and autunite [Ca(UO2)2(PO4)2]), which are structurally similar to chernikovite. In the presence of sodium, the dissolved U(VI) concentrations were generally in agreement with equilibrium predictions of sodium autunite solubility. However, in the calcium-containing systems, the observed concentrations were below the predicted solubility of autunite, suggesting the possibility of uranium adsorption to or incorporation in a calcium phosphate precipitate in addition to the precipitation of autunite.
AB - Uranyl phosphate solids are often found with uranium ores, and their low solubility makes them promising target phases for in situ remediation of uranium-contaminated subsurface environments. The products and solubility of uranium(VI) precipitated with phosphate can be affected by the pH, dissolved inorganic carbon (DIC) concentration, and co-solute composition (e.g. Na+/Ca2+) of the groundwater. Batch experiments were performed to study the effect of these parameters on the products and extent of uranium precipitation induced by phosphate addition. In the absence of co-solute cations, chernikovite [H3O(UO2)(PO4)·3H2O] precipitated despite uranyl orthophosphate [(UO2)3(PO4)2·4H2O] being thermodynamically more favorable under certain conditions. As determined using powder X-ray diffraction, electron microscopy, and laser induced fluorescence spectroscopy, the presence of Na+ or Ca2+ as a co-solute led to the precipitation of sodium autunite ([Na2(UO2)2(PO4)2] and autunite [Ca(UO2)2(PO4)2]), which are structurally similar to chernikovite. In the presence of sodium, the dissolved U(VI) concentrations were generally in agreement with equilibrium predictions of sodium autunite solubility. However, in the calcium-containing systems, the observed concentrations were below the predicted solubility of autunite, suggesting the possibility of uranium adsorption to or incorporation in a calcium phosphate precipitate in addition to the precipitation of autunite.
KW - Autunite
KW - Environmental remediation
KW - In situ immobilization
KW - Phosphate
KW - Uranium
UR - https://www.scopus.com/pages/publications/84890880737
U2 - 10.1016/j.chemgeo.2013.12.002
DO - 10.1016/j.chemgeo.2013.12.002
M3 - Article
AN - SCOPUS:84890880737
SN - 0009-2541
VL - 364
SP - 66
EP - 75
JO - Chemical Geology
JF - Chemical Geology
ER -