Antonio DE SOUZA BRAGA NETO1, Baptiste RIGAUD2, Anne-Laure ROLLET1, Guillaume MÉRIGUET1, Juliette SIRIEIX-PLÉNET1
1Sorbonne Université, CNRS, Physicochimie des Électrolytes et Nanosystèmes Interfaciaux, Paris, France
2Sorbonne Université, Fédération de Chimie et Matériaux de Paris Centre, Paris, France
The constant increase in critical metals demand promotes innovation efforts toward recycling. Platinum (Pt) is a highly valuable and strategic platinum-group element (PGE), which is extensively used in, catalysts, aviation, pharmaceutical industry, and several other applications .
The recycling of critical metals is mainly carried out by a succession of stages. One of these stages is the liquid-liquid extraction, which is basically the distribution of solutes between two immiscible liquids in contact with each other. The current industrial processes use large amounts of toxic volatile organic solvents and extractants. Ionic liquids (ILs) appear then as a valuable alternative to replace volatile organic solvents since they are less toxic, flammable, and volatile than conventional solvents . Thermomorphic ILs can be applied in homogeneous liquid-liquid extraction (HLLE). This process takes advantage of liquids that exhibit temperature-dependent miscibility behavior with aqueous solutions . In the homogeneous state, the interface disappears and there is no diffusion barrier for extraction. However, the extraction mechanisms of these IL systems are not fully understood.
This work focuses on the platinum HLLE and on the understanding of the mechanism at play. NMR spectroscopy is used to fill the gaps in understanding the process since this technique allows to observe the different species present in the system, such as extractant, cation, and anion of the IL, following different nuclei. In this work, various NMR techniques are used to give structural and dynamical insights into the extraction processes. In particular, the distribution of the different species within the sample is obtained during the whole extraction. Additionally, interactions between species and, diffusion processes can also be determined. Simultaneously, the key parameters for the liquid-liquid extraction efficiency, such as extractant concentration, phase ratio, and metal concentration. are studied. This approach will allow a comprehensive understanding of the process during the extraction.
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