Electrochemical Processing of Planetary Regolith in Molten Salts – A Review

Molten Salt Electrolysis (MSE) is a process for extracting oxygen and metals from planetary regolith, contributing to decreasing launch masses and enabling sustainable long-term exploration of the Moon and Mars. MSE offers unique advantages: it tolerates heterogeneous oxide feeds while operating at significantly lower temperatures than alternative thermo- and electro-chemical processes, using a minimal amount of consumables. Two principal MSE technologies, Hall–Héroult electrolysis and the FFC process, are evaluated in terms of their relevance to the space resources field. Drawing on terrestrial heritage, technology gaps that emerge when these processes are translated into extraterrestrial environments are identified. Both technologies are examined in detail across parameters central to regolith processing: anode material, operating temperature, electrolyte composition, feedstock pretreatment, oxide solubility, cathode material, reduction throughput, faradaic efficiency, and the composition of both metallic and gaseous products. This integrated assessment ultimately allows the identification of critical development priorities ranging from anode and cathode durability to electrolyte lifetime and extraterrestrial reactor adaptations, guiding and accelerating the advancement of MSE towards practical off-Earth implementation.