The study of the speciation of uranyl-sulphate complexes by UV-Vis absorption spectra decomposition

Uranyl-sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO(2)(NO(3))(2) + Na(2)SO(4) solutions of different Phi(S) = [SO (4) (2-) ]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO(2)(NO(3))(2) + NaNO(3) solutions with different Phi(N) = [NO (3) (-) ]/[U(VI)] ratio at pH = 2 were also measured. The effects of Phi(S) and Phi(N) ratios value were most pronounced in wavelength interval 380-500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO(2)SO(4), UO(2)(SO(4)) (2) (2-) , UO(2)NO(3) (+) and UO(2)(NO(3))(2) coincided well with published data, but those for UO(2)(SO(4)) (3) (4-) and UO(2)(NO(3)) (3) (-) were significantly lower.