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Mineral nanodroplets: ultrafast microfluidic mixers as a tool to decipher their mechanisms of formation

Contact: CHEVALLARD Corinne, , corinne.chevallard@cea.fr, +33 1 69 08 52 23
By implementing ultra-fast microfluidic mixers (t_mix <1 ms), the intern will participate in the study of a precipitation reaction modeling a key-step of rare earth recovery. This will allow better characterizing the formation of a liquid nanophase, very recently reported.
Possibility of continuation in PhD: Oui
Deadline for application:30/03/2022

Full description:
Our “green economy” (photovoltaics, lithium batteries) largely relies on the rare-earth (RE) elements; but their extraction raises heavy ecological concerns, and their recycling is scarce. Any progress in the separation and precipitation processes will benefit the global environmental balance.

Our recent study of the co-precipitation of cerium ions by oxalic acid in water, a key step in some recovery process of RE, has revealed the spontaneous formation of “mineral nanodroplets” right after reagent mixing. These nanodroplets consist in a reactant-rich liquid that convert into cerium oxalate crystals after several tens of seconds. This newly reported nanophase could benefit separation and recovery processes, but its conditions and mechanisms of formation needs a deeper investigation.

Its thorough characterization implies being able to probe the system just after mixing, when the system still consists of free ions. This is achievable thanks to ultrafast microfluidic mixers (tmix < 1 ms), fabricated using soft-lithography techniques, and recently used by our team to study calcium carbonate precipitation by X-ray scattering.

The aim of this internship is to set up the conditions for a routine use of these microfluidic mixers in the framework of RE separation. To this end, we plan to 1) ease the production of microfluidic mixers thanks to the use of alternative fabrication routes; 2) demonstrate the effectiveness of these mixers in determining the conditions and mechanisms for the appearance of the mineral nanodroplets with laboratory techniques.

• Binnemans, K., et al. Journal of Cleaner Production, 2013, 51, 1-22.
• De Yoreo, J. J., et al. Science 2015, 349, aaa6760.
• Lu, Z., et al., Sens. Actuators B Chem. 2010, 144, 301–309.
Technics/methods used during the internship:
Soft lithography, solution chemistry, optical microscopy, luminescence spectroscopy, cryo-TEM

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