Metal Recovery from Lunar Regolith via Deep Eutectic Solvent Electrolysis for In Situ Resource Utilization

Sustaining human presence on the Moon depends on access to strategic metals, which can be achieved by directly utilizing extraterrestrial resources through in situ resource utilization (ISRU). This study presents novel insights and preliminary results into a previously unexplored strategy for metals extraction from the lunar regolith simulant Lunar Mare Soil (LMS-1) using deep eutectic solvents (DESs). Based on inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements, the solubility of major oxide components of the regolith, SiO₂, Al₂O₃, TiO₂, Cr₂O₃, MgO and FeO_T, was investigated in ethaline (choline chloride:ethylene glycol, ChCl:EG) as well as reline (ChCl:Urea). Although both DESs enabled oxide dissolution, reline exhibited significantly higher dissolution efficiency, due to the additional hydrogen-bond donor sites, NH and CO groups from urea, as well as high chloride activity in the reline. Cyclic voltammetry (CV) and square wave voltammetry (SWV) revealed that dissolved metal species in the reline-regolith system undergo complex multivalent redox transitions. The equilibrium potentials of the metals were determined and correlated with the order in which the metals should be electrodeposited on the cathode from an electrolyte containing dissolved lunar regolith. Based on the data from electrochemical measurements, parameters for electrolysis were selected. At less negative overpotentials, the deposit consisted mainly of Si, while Al, Cr, and Fe, along with Si, were electrodeposited at more negative potentials. The results highlight the importance of considering the selective electrochemical extraction of metals from DESs using lunar regolith as the source.