Solubility and Solvation of Metal Species in Ionic Liquids

The use of ionic liquids (ILs) for metal separations processes is a developing field. The use of systems of ILs with dissolved metals could lead to the development of electrolyte solutions, metal electrodeposition processes, liquid-liquid metal extraction processes and new material design. In order to develop new processes using metal-IL mixtures, physical property data and fundamental understandings of metal-IL interactions are needed. In this work the measurement of fundamental physical properties and phase equilibria are combined with spectroscopic characterization of metal-IL systems to better understand solute-solvent interactions between metals and ILs. ILs can be designed to have a specific functional group that binds to a metal, or ILs can be designed to share a common anion with a metal salt. ILs with specialized functional groups, or task specific ILs, are investigated through UV-vis and Raman spectroscopy to understand the IL-metal complexes that are formed and how this behavior effects metal solubility. The temperature dependent solubility of lithium salts in ILs with a common anion has been measured to better understand how the physical properties of an IL affect the solubility. The effect on metal salt solubility in an IL when tuning the properties of the cation is important to designing processes that retain high metal solubilities but allow for adjusting other physical properties of the IL solvent. The solid liquid equilibria measurements in this work have also shown that the solubility of a metal salt in an ionic liquid results in activity coefficients below 1, and that the data can be fit to the Wilson Equation in some cases. The role of water in an IL-metal mixture has also been investigated. Water can play an important role as a cosolvent for an IL, affecting the physical properties of the IL-metal mixture. Water can also interact with a metal species in an IL, affecting the metal solubility through solvation. Mixtures of IL, water and Nd2O3 have been investigated in this work through liquid-liquid equilibria to examine the effect of metal loading. Near infrared spectroscopy has been utilized to quantify water in ILs and to characterize the state of water in IL-metal mixtures.