Sulfato Complex Formation of V(V) and V(IV) in Pyrosulfate Melts Investigated by Potentiometry and Spectroscopic Methods

By combined potentiometric, ESR and VIS/NIR spectroscopic measurements the coordination of SO4,2- to V(IV) and V(V) in M2S2O7-M2SO4-V2O5 (M=K and Cs) melts, respectively under SO2(g) and O2(g) atmospheres at 450 - 470 °C, has been investigated. The results for both systems are in accordance with the oxo sulfato vanadate equilibria VO(SO4)2,2- + SO4,2- = VO(SO4)3,4- for V(IV) and (VO)2O(SO4)4,4- + 2SO4,2- = 2VO2(SO4)2,3- + S2O7,2- for V(V), and 2VO2(SO4)2,3- + SO2 + SO4,2- 2VO(SO4)3,4- for the V(V)-V(IV) redox reaction in melts saturated with sulfate. Constants for these equilibria have also been obtained, as well as characteristic EPR parameters and molar absorptivities for the complexes. In addition, the mole fractions of M2SO4 in the M2S2O7-M2SO4/SO2(g) systems saturated with M2SO4 were found to be 0.05019 for M = K at 450 C and 0.07002 for M = Cs at 470°C, respectively.