Dioxouranium(VI) oxalate complexes

The complex formation between dioxouranium(VI) and oxalate ion has been inv estigated, at 25.00 degrees C, in 2 and 3 M NaClO4, by measuring the potent ials of a glass and of a Hg2C2O4-Hg electrode. In the analysed solutions th e upper limit of the uranium(VI) concentration did not exceed 0.03 M, the o xalate concentration was imposed by the modest solubility of its sodium sal t in the ionic media (about 0.015 M in 3 M NaClO4) and the acidity was kept at levels higher than 0.01 M in order to hinder formation of hydrolysed an d possible ternary species. The measurements have been interpreted by assum ing the formation of mononuclear complexes only, according to the reaction UO22+ + p C(2)O(4)(2-)reversible arrow UO2(C2O4)(p)((2 - 2p)+). The equilib rium constants have been extrapolated to infinite dilution by applying the Specific Interaction Theory (SIT) and, in weight molarity (molality) units, are log (0)beta(1) = 7.38 +/- 0.07, log (0)beta(2) = 11.7(2) +/- 0.1, log (0)beta(3) = 13.6 +/- 0.2. Under the same experimental conditions the proto lysis constants of oxalic acid and several interaction coefficients, necess ary for extrapolation of the results to the thermodynamic scale of activiti es, through the SIT, have also been determined.