Abstract: This work reports the optimization strategy for the design of a microfluidic platform to achieve the separation and recovery of aqueous mixtures of rare earth elements (REEs); the work showcases the separation of dysprosium, neodymium and lanthanum using microextraction modules with an organic phase constituted of Cyanex® 572 diluted in Shellsol® D70. An optimization model has been developed to assist in the design of the number of stages (microextractors, settling tanks and mixer and splitter units) and the best operational conditions that maximize the separation and recovery targets. Results predicted by the model with a configuration composed of 4 microreactors have been experimentally evaluated. Starting with 1 mM equimolar REE mixtures and 301 mM Cyanex® 572 as the organic phase, the model shows that REE recovery and concentration improve with an increasing number of microextractors. Using eight microextractors, along with optimised pH and recycling, recoveries exceed 92 %, purities reach 93 %, and concentrations are at least six times higher than the feed. The REEs extraction microfluidic platform has been 3D printed with a modular LEGO® type design that fa cilitates reconfiguration and scalability. Together with the optimisation model, this platform represents a valuable tool for the design and implementation of future critical element mixtures microextraction applications.

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