Fe-Si alloys extraction via carbothermal reduction of lunar regolith

The emerging field of astrometallurgy is set to play a crucial role in enabling metal production on the Moon. This paper focuses on Fe-Si alloy production from the lunar regolith using carbothermal reduction. Thermodynamic modelling was conducted to understand the effects of varying carbon, temperature, and pressure on the regolith reduction. Modelling results predict that ideal parameters for the extraction of liquid Fe-Si alloys from lunar regolith under terrestrial conditions are 2 wt.% carbon at 1600°C. Modelling results also predict that higher reduction temperature leads to increased impurities such as Ti, P and Mn in the Fe-Si alloy. Effects of varying carbon content on the composition and viscosity of the slag are also discussed. Thermodynamic modelling under lunar vacuum conditions (3×10 -15 bar) predicted that Fe-Si alloy forms as solid phases below 650°C, while Fe and Si transition to the gas phase at higher temperatures. The thermodynamic prediction results under terrestrial conditions were verified through experiments. The Fe-Si alloy produced from regolith reduction with 2 wt.% carbon resulted in easy slag-metal separation, and the Fe-Si alloy contained about 7 to 8 wt.% Si with about 1 wt.% P. At 4 wt.% carbon, Si content in the Fe-Si increased to 15 wt.% and the alloy contained about 1 to 2 wt.% P. With the further rise in carbon to 6 and 8 wt.%, Ti formed an intermetallic Ti-rich phase with Si and Fe. These findings support the viability of extracting Fe-Si alloy from lunar regolith through carbothermal reduction.