Metals extraction on Mars through carbothermic reduction

Abstract

In situ resource utilization (ISRU), and specifically the extraction and production of structural metals from Martian soil, is important for supporting further exploration, habitat and industrial developments on Mars. Considering Mars's atmospheric conditions and soil compositions, systematic analyses (supported by thermodynamic calculations) on possible metal extraction processes have been carried out. The analyses suggest that carbothermic reduction of Martian regolith would be the preferable starting point considering the abundance of carbon in the form of CO2 in the Martian atmosphere. It was proposed that carbon would be sourced from the cooling of carbon monoxide produced from CO2 electrolysis (MOXIE) from the Martian atmosphere. An Ellingham diagram showing the relative stability of oxides at Mars's atmospheric pressure of 7 mbar has been constructed; detailed equilibrium calculations to evaluate the carbothermic reduction of Martian regolith have also been carried out. The thermodynamic calculations predicted the formation of liquid Fe alloy with 99.9% conversion when the regolith was reacted with carbon (at approximately 10 wt% addition) at 1120 °C and 7 mbar. The impurities in the liquid Fe alloy were predicted to be mainly Si, C, Cr, and P. The hot gas produced from the process was predicted to be rich in CO (91%) and could be used for the preheating of the regolith. The CO could also be recycled and condensed to produce C (that could be re-used for the carbothermic reduction). The minimum energy requirement for the carbothermic reactor was calculated to be 3.37 MWh/tonne of liquid iron alloy (while the total energy requirement including MOXIE and agglomeration was calculated to be 15.51 MWh/tonne of liquid iron alloy). A generic process flowsheet has been developed considering these results.