Sulfate complex formation of V(V) and V(IV) in pyrosulfate melts investigated by potentiometry and spectroscopic methods

By combined potentiometric, electron paramagnetic resonance (EPR), and visi ble/near-infrared spectroscopic measurements, the coordination of SO42- to V(IV) and V(V) in M2S2O7-M2SO4-V2O5 (M = K and Cs) melts, respectively, und er SO2(g) and O-2(g) atmospheres at 450-470 degrees C has been investigated . The results for both systems are in accordance with the oxo sulfate vanad ate equilibria VO(SO4)(2)(2-) + SO42- reversible arrow VO(SO4)(3)(4-) for V (IV), (VO)(2)O(SO4)(4)(4-) + 2SO(4)(2-) reversible arrow 2VO(2)(SO4)(2)(3-) + S2O72- for V(V), and 2VO(2)(SO4)(2)(3-) + SO2 + SO42- reversible arrow 2 VO(SO4)(3)(4-) for the V(V)-V(IV) redox reaction in melts saturated with su lfate. Constants for these equilibria have also been obtained, as well as c haracteristic EPR parameters and molar absorptivities for the complexes. In addition, the mole fractions of M2SO4 in the M2S2O7-M2SO4/SO2(g) systems s aturated with M2SO4 were found to be 0.050 19 for M = K at 450 degrees C an d 0.070 02 for M = Cs at 470 degrees C, respectively.