On the hydrolysis of the dioxouranium(VI) ion in sulfate solutions.
The formation of ternary UO2(2+)-(OH-)-SO4(2-) complexes has been studied at 25 degrees C in 3 M NaClO4 ionic medium by measurements with a glass electrode. The solutions had uranium concentrations between 0.3 and 30 mM, sulfate between 20 and 200 mM, and 1.66 < or = [SO4(2-)]/[U(VI)] < or = 300. The hydrogen ion concentration ranged from 10(-3) M to incipient precipitation of basic sulfates. This occurred, depending on the metal concentration, at [H+] between 10(-4) and 10(-5.3) M. In the interpretation of the data the stabilities of binary complexes were assumed from independent sources. The data could be explained with the mixed complexes and equilibria (beta(pqr)(3sigma) refers to pUO2(2+) + qH2O + rSO4(2-) <==> (UO2)p(OH)q(SO4)r(2p-q-2r) + qH+): logbeta222 = -2.94 +/- 0.03, logbeta341 = -9.82 +/- 0.06, logbeta211 = -0.30 +/- 0.09, logbeta212 = 1.09 +/- 0.09, logbeta351 = -15.04 +/- 0.09 and logbeta462 = -14.40 +/- 0.06. The fit could be improved by including UO2OH+ with logbeta110 = -5.1 +/- 0.1. The identity of the minor species remains, however, an open question.
Dipartimento di Chimica dell'Università "Federico II", Via Cinthia 45, 80126-Napoli. ciavatta@chemistry.unina.it
Liberato
L
Ciavatta
Gaetano
G
De Tommaso
Mauro
M
Iuliano
D006868:Hydrolysis; D006878:Hydroxides / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D009994:Osmolar Concentration; D011199:Potentiometry; D012996:Solutions; D013431:Sulfates / Q000737:chemistry*; D017974:Uranium Compounds / Q000737:chemistry*
D006878:Hydroxides; D012996:Solutions; D013431:Sulfates; D017974:Uranium Compounds; C012597:uranium dioxide