Voltammetric Study of Uranyl–Selenium Interactions. Part 2. Uranyl(V) Selenate Complex

Under the influence of recently published papers and some older own results, complex formation in uranyl(VI)-selenium(VI) system was reinvestigated at the ionic strengths of 0.1 and 3.0 mol L-1. Using electrolyzed selenate solutions (and square-wave voltammetry as a measuring technique) two coordination species at the higher electrolyte concentration (log beta(1) = 1.48 +/- 0.01, log beta(2) = 2.4 +/- 0.1) were recognized, in agreement with the literature data based on other experimental methods. For successful interpretation of the voltammetric data, previously unknown weak complex (log beta(01)=0.7 +/- 0.1) of the reduction product, i.e. uranyl(V) should also be included in the model. At the lower electrolyte concentration (0.1 mol L-1), formation of complexes other than UO(2)Seo(4)(0) cannot be unambiguously confirmed due to the narrow ligand concentration range.Concerning the number of coordination species and their stability constants, seemingly different results that arise from voltammetry and other (independent) experimental methods reflect the fact that the former, in addition to the complexation of initially present metal ion, "sees" the coordination of its reduction product with the ligand of interest, too. When both processes are taken into account during treatment of voltammetric data, such differences disappear.