Physicochemical properties of lunar regolith simulant for in situ oxygen production

TL;DR

This paper tackles in situ oxygen production for lunar settlements by examining how regolith composition and processing influence oxygen accessibility. It validates high-fidelity simulants LHS-1, LHS-2, and LSP-2 using SEM-EDX, XRD, BET, and hydrogen temperature-programmed reduction (TPR) to evaluate mineralogy, texture, and reducibility, alongside gas adsorption studies. Although ilmenite (FeTiO$_3$) is the most readily reducible oxide via the hydrogen pathway $FeTiO_3 + H_2 \rightarrow Fe + TiO_2 + H_2O$, bulk highland simulants (notably LHS-2) exhibit favorable reduction and adsorption behavior due to distributed Fe-bearing silicates and microstructural features, underscoring the primacy of whole-regolith responses over ilmenite content alone. These findings support whole-regolith processing strategies for lunar ISRU and guide the design of oxygen extraction systems for highland and polar regions, where ilmenite abundance is limited yet regolith complexity can enhance overall performance.

Abstract

Permanent lunar settlements will rely on in situ oxygen production from regolith for life support and propulsion. While oxygen is abundant in lunar materials, it is chemically bound within metal oxides whose extractability depends strongly on regolith composition and processing strategy. In this study, we validate and characterize high-fidelity lunar regolith simulants representative of the lunar highlands and south pole using scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area and pore structure analysis, and hydrogen temperature-programmed reduction. The simulants exhibit strong mineralogical and compositional fidelity to returned Apollo and Chang'e samples, with ilmenite confirmed as the most readily reducible oxygen-bearing phase. However, despite low ilmenite abundance, bulk highland simulants display favorable reduction behavior arising from distributed Fe-bearing silicate and glassy phases, as well as surface and microstructural properties that influence gas-solid interactions. Adsorption experiments with gases (H2, CH4, and CO2) and water indicate that mineralogical heterogeneity and pore accessibility influence their uptake in simulants. These results indicate that oxygen extraction behavior in realistic lunar regolith is governed by whole-regolith response rather than ilmenite content alone, supporting the option of whole-regolith processing strategies for oxygen production in lunar in situ resource utilization architectures.

Figures (7)

• Figure 1: EDX elemental maps of lunar regolith simulants: (a) LHS-2 (left) and (b) LSP-2 (right).
• Figure 2: EDX elemental map of LHS-2 simulant.
• Figure 3: EDX elemental map of LSP-2 simulant.
• Figure 4: XRD patterns of LHS-1 (top), LHS-2 (middle), LSP-2 (bottom), and their constituent minerals.
• Figure 5: TPR Profiles of LHS and LSP (top), Ilmenite (bottom).