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REE-CYCLE Report Summary

Project ID: 320915
Funded under: FP7-IDEAS-ERC
Country: France

Mid-Term Report Summary - REE-CYCLE (Rare Earth Element reCYCLing with Low harmful Emissions)

Eight teams of research located at Marcoule and Grenoble are associated to develop a high throughput method to determine the selectivity of ion phase transfer in multi-component chemical systems: towards predictive modelling of extraction; early detection of phase transitions on single active droplet . Improvement of knowledge will allow to build-up predictive models of yield and selectivity. This will allow to perform extractant-less or solvent-less greener liquid-liquid extraction methods, assisted by ultra-sound or mega-sound triggering.

Liquid-liquid extraction is a crucial process for recycling chemistry. The largest identified “urban mine” will be rare earth-based magnets. In order to recycle for instance rare earths and to avoid mining of new rare earths, recycling has often to be performed by separating and purifying the rare earths from iron. This known technology relies on ion equilibria in coexisting phases located between binodal tie-lines in the Winsor II regime of a microemulsion with excess brine. Since the systems contain at least seven components, the phase diagram in seven dimensions must be projected in tetrahedrons, as a result, high “safety” margins are taken, including using more than minimal possible quantity of acid.

The selectivity and differences of free energy of transfer can be determined with good reliability and with reasonable time: days instead of months needed by batch methods. Availability of data with variable composition allows to challenge the very few predictive models based on first principles and evaluating the free energy of transfer terms.

At the end of 2015, we have obtained the first results with a micro-fluidic device allowing continuous exploration of lines in a complex phase diagram. We model the ion and extractant distribution and separation, and compare to expected values from available theories. Finally we discuss how to further speed up the process by electroacoustic fields.

This complementarity of methods necessary to achieve our goal needs integrating closely statistical physical chemistry, colloid science, chemical engineering adapted first to optimizing and hence rendering possible rare earth recycling in acceptable economic, legal and environmental conditions of rare earths coming from minerals. This occurs to be but so general, that they could be adapted to wood impregnation as well as for pesticide/polyphenol separation in biomass treatments. Unexpected output was the first known theoretical parameter-free explanation of efficient extraction known and not understood as “Eau de Cologne” (Zemb, T et al. PNAS 2016).

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