Oxygen extraction from lunar dry regolith: Thermodynamic numerical characterization of the carbothermal reduction

In Situ Resource Utilization constitutes an enabling technology for future, long-term human space exploration. The potentiality of oxygen extraction from dry lunar regolith by means of carbothermal reduction is analyzed in this work. Focus is placed on the scarcely investigated temperature range 1273-1373K, looking at the possibility to operate below the regolith melting point. The first aspect to consider is to properly identify candidate species and reaction paths that can lead to oxides reduction. This is achieved by modeling the Gibbs free energy Delta G degrees trend for suitable reactions, looking at which species can react in the temperature range of interest among the minerals and oxides present in the regolith. A more detailed investigation is presented for the SiO2 and TiO2 oxides families, being both particularly attractive: the former for its ubiquitous presence in the lunar soil, the latter for its importance in past ISRU literature and its local peaks of concentration in specific areas on the Moon. Finally, a preliminary indication on the expected contribution of each species to the total yield is given.