The carbothermal reduction of lunar regolith under high-vacuum conditions

In the interest of evaluating novel options for space in situ resource utilisation (ISRU), the viability of solid state carbothermal reduction for metal extraction from lunar regolith was investigated. The FactSage thermochemical modelling software package was used to predict the effect of temperature and pressure on the reduction of lunar regolith material by solid carbon. It was predicted that the reduction of iron and silicon is thermodynamically viable at sub liquidus temperatures (<1100 °C) when conducted at a pressure of 10 −12 atm or below. For the modelled system the predicted ideal temperature/pressure band for operation is 1500 °C at 10 −3 atm, 1050 °C at 10 −6 atm, 850 °C at 10 −9 atm, and 700 °C at 10 −12 atm. These conditions are predicted to be the highest temperatures possible for reaction while still resulting in the reduced Fe and Si remaining in the solid or liquid phase. This work demonstrates the theoretical reduction in energy requirements for metal production when conducted under high-vacuum conditions. • The natural vacuum on the Moon can reduce the energy requirement for metal production on the lunar surface. • The carbothermal reduction of regolith is thermodynamically viable at sub liquidus temperatures on the Moon. • Modelling predicts that Fe and Si can be reduced from lunar regolith at 850 °C at 10 −9 atm, and 700 °C at 10 −12 atm. • Some astrometallurgical processes can be more energy efficient if operated under vacuum conditions.