Kinetics of the actinides-lanthanides separation: mass transfer between molten fluorides and liquid metal at high temperatures

Experimental studies on the extraction of actinides and other elements from a fluorinated salt into a liquid metal phase containing a reducing agent such as magnesium or aluminium have been performed using two different systems. The rate of transfer is very rapid and could, depending on the way stirring is carried out, vary with the stirring rate. Three different types of stirring have been tested and observations are explained both in terms of hydrodynamics and chemistry. The role of interfacial agitation is discussed and the assumption that the limiting factor is related to the chemical reaction and not mass transfer is confirmed by a measured activation energy of 180 kJ mol−1. Thermal effects are observed with different magnitudes depending on the reduced species. Chemical control of the kinetics combined with thermal effects account for the rapid transfer. These results can be used to develop a high-temperature process for separating actinides and lanthanides. More work is required to determine the reaction mechanisms, which may not be limited to the interface.