Magnetic resonance imaging: an innovative approach to observe rare metal extraction using ionic liquid

Abstract

In the present work, a novel approach has been made to evaluate the extraction mechanism of neodymium (Nd) using trihexyl-tetradecyl-phosphonium benzoate (TTPB) ionic liquid through nuclear magnetic resonance (NMR) techniques. A detailed study on the interactions between the extractant (Nd) and the ionic liquid (IL) is presented. The ¹H NMR spectral analysis confirmed that Nd extraction took place through the benzoate anion. Furthermore, the NMR relaxation time of the anion is greatly affected affirming that Nd extraction indeed took place through the benzoate anion. This change in the relaxation time caused by the Nd ion on the protons in the anion and cation in TTPB has been used to visualize the extraction mechanism using ¹H MRI. A strong change in the image intensity with respect to the time observed in the IL phase validates the extraction of Nd from the aqueous phase into the IL phase. Also, combining the ¹H NMR, diffusion coefficient, Karl-Fischer and ultraviolet-visible absorption spectroscopic (UV-Vis) results, we have elucidated the co-ordination structure around Nd during the extraction process.