Reactive components and alkali leaching behavior of lunar regolith simulant for geopolymer production

To address the core challenge of extreme heterogeneity in lunar regolith composition constraining precise regulation of geopolymer properties, this study analyze the alkali activation characteristics of lunar regolith simulant (HIT-L-2) and its regulatory mechanisms on geopolymer performance following an analytical progression from raw material mineral composition to reaction activity and finally to mechanical properties. The study revealed that the amorphous phase in HIT-L-2 exhibits the highest reactivity, while crystalline phase dissolution requires a temperature threshold, with reactivity following the order: olivine > pyroxene > plagioclase. Significant differences in dissolution activation energies were observed between Si and Al elements (E_a^Si=86.75–95.97 kJ/mol；E_a^Al =64.44–74.07 kJ/mol), resulting in the Si/Al molar ratio in leachates increasing from 2.01 to 4.16 under intensified leaching conditions. The compositional structure of mineral phases in raw materials and alkali leaching parameters (temperature, alkali concentration, duration) jointly govern elemental dissolution behaviors, consequently affecting product composition and microstructure of geopolymers. Critically, the compressive strength of geopolymers exhibits a strong positive linear correlation (R > 0.95) with Si and Al leaching rates, and geopolymer blocks with substantial compressive strength (16–29 MPa) were only achieved when curing temperature reaches 90°C. Understanding these composition-property relationships under terrestrial conditions provides a preliminary reference for the potential on-demand design of lunar regolith geopolymers, pending further validation in lunar-relevant environments.