Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method.
The formation constants of ternary complexes (MUO2(CO3)3(2-) and M2UO2(CO3)3(0)) of uranyl and carbonate with alkaline earth metals (M2+ denotes Mg2+, Ca2+, Sr2+, and Ba2+) were determined with an anion exchange method by varying the metal concentrations (0.1-5 mmol/L) at pH 8.1 and a constant ionic strength (0.1 mol/L NaNO3) under equilibrium with atmospheric CO2. The results indicate that the complexes of MUO2(CO3)3(2-) and M2UO2(CO3)3 are simultaneously formed for Ca2+ and Ba2+, while Mg2+ and Sr2+ form only the MUO2(CO3)3(2-) complex under our experimental conditions. The cumulative stability constants for the MUO2(CO3)3(2-) complex obtained at / = 0 are as follows: logbeta113 = 26.11 +/- 0.04, 27.18 +/- 0.06, 26.86 +/- 0.04, and 26.68 +/- 0.04 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively. For M2UO2(CO3)3(0), the value of logbeta213 at / = 0 was measured to be 30.70 +/- 0.05 and 29.75 +/- 0.07 for Ca2+ and Ba2+, respectively. Based on the formation constants obtained in this study, speciation calculations indicate that at low Ca2+ concentration (e.g., <2.2 mmol/L), CaUO2(CO3)3(2-) is more important than Ca2UO2(CO3)3 and that the Ca2UO2(CO3)3 distribution increased with increasing Ca2+ concentration. Uranium sorption onto anion-exchange resins is inhibited by the formation of the neutral Ca2UO2(CO3)3(0) species.
Dong
Wenming
W
Oak Ridge National Laboratory, Environmental Sciences Division, P. O. Box 2008, MS 6038, Oak Ridge, Tennessee 37831-6038, USA.
Brooks
Scott C
SC
D000327:Adsorption; D000837:Anion Exchange Resins / Q000737:chemistry*; D001464:Barium / Q000737:chemistry; D002118:Calcium / Q000737:chemistry; D002254:Carbonates / Q000138:chemical synthesis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry; D008673:Metals, Alkaline Earth / Q000737:chemistry*; D008956:Models, Chemical; D013324:Strontium / Q000737:chemistry; D017974:Uranium Compounds / Q000138:chemical synthesis* / Q000737:chemistry
D000837:Anion Exchange Resins; D002254:Carbonates; D008673:Metals, Alkaline Earth; D017974:Uranium Compounds; D001464:Barium; D008274:Magnesium; D002118:Calcium; D013324:Strontium