Cathodic processes in Li2MoO4–K2MoO4–MoO3 and K2MoO4–MoO3 melts containing added UO2MoO4 were investigated at 550–800 °C using cyclic voltammetry, cathodic polarization and bulk electrolysis. Cathodic reduction of molybdate melts (not containing uranium) resulted in formation of molybdenum dioxide. Products of the cathodic reactions in the melts containing uranium molybdate predominantly consisted of crystalline uranium oxides (mostly UO2 and U4O9) and MoO2. Minor products formed included other uranium oxides (U3O8, U13O34), mixed uranium-molybdenum oxides (U1.5Mo10O32, Mo2UO8) and molybdates (provisionally attributed to K2U(MoO4)3). Effect of temperature, cathodic current density 0.05–1 A cm−2), excess MoO3 concentration (30–50 mol%) on the composition of the cathodic reaction products were analyzed. Oxygen-to-uranium atomic ratio (oxygen coefficient) for primary uranium oxide phases was determined and varied from 1.963 to 2.161 for UO2±x and from 2.209 to 2.287 for U4O9±y. The effect of the electrolysis regime on the composition of the cathodic product was also considered. Constant-current and constant-potential electrolysis, as well pulsed-current, pulsed-potential and pulsed-reversed-current electrolysis were investigated with varying the parameters of alternating pulses (duration, current density or potential). Chemical and phase composition of the products produced by bulk electrolysis was fully characterized.
