Possible routes for pyrochemical separation: Focus on the reductive extraction in fluoride media

Abstract

Molten salts (MSs) such as fluoride or chloride salts at high temperature (400–800 °C) are solvents known for their high solvation power and electroactivity range. Rare earths, lanthanides, actinides, and refractory metals can be dissolved, treated, and purified in MSs. The properties of these solvents are particularly interesting for nuclear spent-fuel reprocessing. The pyrochemical separation and extraction of solutes can be performed using several methods taking into account the effects of redox and/or acidity. This paper is focused on the reductive extraction method performed by contacting a liquid metal (LM) containing reductive species and an MS. The analytical model developed to calculate the efficiency of such a method is detailed in this paper. To apply this model, one essential point is the establishment of a database related to the redox and solvation properties of solutes in MSs. The approach retained to propose a database based on the analysis of both thermochemical data of pure compounds and experimental measurements reported in the literature is described in this paper in the case of lanthanides in fluoride MSs. The use of the database to calculate efficiency as a function of process parameters is given in this paper as well as the comparison between two reducing agents considered.