DIRECT SPECTROSCOPIC SPECIATION OF URANIUM(VI) IN CARBONATE SOLUTIONS

UV-Vis absorption spectra of uranium(VI) in the wavelength range of 35 0 nm to 580 nm are recorded as a function of pH for solutions in solid -liquid phase equilibrium with UO2CO3(s) in a perchlorate medium at I = 0.1 M and 25 degrees C under 100% CO2 atmosphere. Quantitative inter pretation of experimental spectra in the pH range of 3.3 to 6.3 is mad e by single component spectra of UO2CO30, UO2(CO3)(2)(2-), UO2(CO3)(3) (4-) and (UO2)(2)(OH)(2)(2+) species. The molar absorbances are found to be 36+/-3 l mol(-1) cm(-1) at 400 nm, ca. 13 l mol(-1) cm(-1) at 41 5 nm and 29.0+/-0.7 1 mol(-1) cm(-1) at 448.2 nm, resp. Evidence for s pectral contributions by (UO2)(2)(OH)(2)(2+) in the pH range of 3.3 to 4.5 is discussed. Formation constants 1g beta(101) = 8.81+/-0.04, 1g beta(102) = 15.5+/-0.4 and 1g beta(103) = 21.74+/-0.22 are obtained fr om peak deconvolution procedure using 32 UV-Vis spectra.