Existence of Three Type of Reverse Aggregates Iin Organic Solvents: Consequences on Observed Cation Distributions between Aqueous and Microemulsion Phases

Cascade Liquid-liquid extraction is a general technology used to extract valuable and toxic cations for recycling of metals. Exploring new formulations and limiting the harmful emissions is the core objective of the REE-CYCLE project¹. This requires the development of predictive models for ion extraction and desextraction in phase diagrams of systems containing at least four components:  a solvent, a co-solvent, water, an acid or a buffer as well as the salts of cations to be separated. Typical example is to separate rare earths versus iron.

In all efficient processes, the extraction relies on aggregation in the solvent phase, mainly in Winsor-II regime. We will show in this talk that at least three different types of aggregates exist. We present molecular modelling of the three types of aggregates ². These can be detected by their scattering signature . We show that  it is necessary to take into account long-range interaction in order  to be able to evaluate without parameter -for the first time to our knowledge- the large difference between the supra-molecular complexation free energy which is the motor for selective separation between metals³.and the much lower effective free energy of transfer that is observed in practical applications.

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