Metal oxide solvation with ionic liquids: A solubility parameter analysis

Ionic liquids (ILs) show excellent promise in digesting Lunar regolith comprising metal silicates and oxides in a cyclical and sustainable manner and they can be recovered at the end of the process, thus facilitating in situ metal separation. However, experimentally identifying an IL with ideal properties, out of several thousand possible formulations, is an expensive and time-consuming process. We report a novel model, using the Support Vector Machine (SVM) approach, which predicts the Hildebrand's solubility parameters of ILs as a function of specific heat and other well documented properties to enable screening of ILs for regolith digestion. The results show excellent agreement with those from the standard definition using molar volume and enthalpy of vaporization, and were validated against observations via experiments where metal oxides were dissolved in ILs screened from the model. Furthermore, as a case study, we performed a Hansen Solubility Sphere analysis aided by experi-mental results. We were able to find the maximum radius R0 of the Hansen Solubility Sphere based on positive solubility results of ZnO in four distinct ILs (C4mim Ac, C4mim HSO4, C2mim Cl, and C2mim Br).

Automated summary

Ionic liquids (ILs) are promising for digesting Lunar regolith and facilitating metal separation. We present a novel model using Support Vector Machine (SVM) to predict ILs solubility parameters and enable screening for regolith digestion. The results are validated by experiments and a Hansen Solubility Sphere analysis, providing valuable insights.