Alkali chloride based melts can be employed as working media in spent nuclear fuels pyrochemical reprocessing. Oxygen is on of common impurities in technology and oxygen species can seriously influence speciation of metals in molten electrolytes. From the other hand, one of the possible ways of separating uranium from rare earth fission products by selective precipitation of uranium oxide. The present work was aimed at studying reactions taking place in chloride melts containing neodymium (III) and uranium (III and IV) ions upon addition of oxygen species. In particular, reactions with oxygen and oxide ions (introduced in form of lithium oxide) were considered.

Thermodynamic modeling of possible reactions was first performed to estimate the possibility of separating uranium from rare earths. The experiments were then conducted in the melts based on LiCl–KCl eutectic, NaCl–KCl equimolar mixture and individual LiCl at 550 ^oC (for LiCl–KCl) and 750 ^oC for all the melts). Reaction of the melts containing NdCl₃, UCl₃ or UCl₄ with Li₂O (at various O^2– to Nd³⁺ (U³⁺, U⁴⁺) mole ratios) and with O₂ was investigated.

High temperature electronic absorption spectroscopy was employed to determine the kinetics of the reactions taking place. Phase composition of the solid phases was characterized by X-ray powder diffraction analysis. Size of the particles in the precipitates formed at various conditions was also determined to assess the feasibility of subsequent separation of the solids from the technological melts.