Basic electrochemical and spectroscopic properties of Cr3+, Cr2+, Fe3+, and Fe2+ were studied to analyze the cyclic redox reactions of Cr and Fe, which may decrease the current efficiency of the electro-winning method using NaCl-2CsCl melts. The formal redox potentials of the Cr3+vertical bar Cr2+ and Fe3+vertical bar Fe2+ couples, E degrees'(Cr3+vertical bar Cr2+) , E degrees'(Fe3+vertical bar Fe2+), in NaCl-2CsCl melts at 923 K were spectroelectrochemically determined to be -0.648 +/- 0.005 V and -0.140 +/- 0.010 Vvs. Cl-2 vertical bar Cl-, respectively. These values were determined by measuring electromotive force and UV-VIS absorption spectra at varying concentration ratios of trivalent and divalent ions. Cyclic voltammetry was also carried out to examine the characteristics of the voltammograms for the Cr3+vertical bar Cr2+ and Fe3+vertical bar Fe2+ couples in NaCl-2CsCl melts. The E degrees'(Cr3+vertical bar Cr2+) determined by the spectroelectrochemical method was close to that determined by cyclic voltammetry (-0.651 +/- 0.006 V vs. Cl-2 vertical bar Cl-). The effect of temperature on the E degrees'(Cr3+vertical bar Cr2+) in NaCl-2CsCl melts was studied by cyclic voltammetry in the range from 823 to 1,023 K (E degrees'(Cr3+vertical bar Cr2+) = 0.00143T - 1.971 +/- 0.005 V vs. Cl-2 vertical bar Cl-). Diffusion coefficients of Cr3+ and Cr2+, DCr3+ and DCr2+, were determined between 823 and 1,023 K to be DCr3+ = 2.23 x 10(-3) exp (-4,135/T) and DCr2+ = 3.34 x 10(-3) exp(-4,106/T), respectively. Molar absorptivities of Cr3+ and Cr2+ in NaCl-2CsCl melts at 923 K were determined to be 77.8 +/- 2.4 M-1 cm(-1) at 17,670 cm(-1) and 48.0 +/- 1.4 M-1 cm(-1) at 9,170 cm(-1), respectively. In addition, the effects of these ions on the cyclic redox reaction of the pyro-reprocessing process were discussed.