Contribution to the solution chemistry of uranium (6)

In the first part, a potentiometric study of the complexes formed by the uranyl ion with the hydroxy ligand has been performed. evidence has been presented for the existence of the following complexes with their respective stability constants (determined at 25 deg. C in 0.1 M ClO4Na medium): UO2OH, logbeta1,-1= -4.39; (UO2)2OH, logbeta2,-1 = -2.22; (UO2)2 (OH)2, logbeta2,-2 = -6.09; (UO2)3(OH)5, log3,-5) = -15.64; (UO2)3 (OH)7, logbeta3,-7 = -24.03. In the second part, a similar investigation has been undertaken on the complex formed by the uranyl ion with carbonate and/or hydroxyl ligands; the latter appearing in neutral or acid media. Evidence has been presented for the existence of the following complexes and their respective stability constants, all determined at 25 deg. C in 0.1 M ClO4Na medium: UO2(CO3)3, logbeta3,1,0 = 21.57. UO2(CO3)2, logbeta2,1,0 = 16.16; UO2CO3OH, logbeta1,1,-1 4.10. In the third part, the solid phases of the system (NO3)2UO2 - NaOH - H2O have been investigated by the method of the residues. In this system the following compounds have been identified: U2O7Na2 and (NO3)2 U6O17 in slightly acid medium. Finally, the solid phases of the system (NO3)2UO2 - CO3Na2 - H2O have been investigated as before. The following compounds have been identified: CO3UO2, in slightly acid medium; an uranyl alkaline carbonate appearing in neutral medium with the formula (UO2CO3)3 (NaOH)2, as well as the corresponding uranates. (author)