Extraction of Silica and Alumina from Lunar Highland Simulant

We present the result of a workbench experiment designed to extract silica (SiO2) and alumina (Al2O3) from the anorthosite (CaAl2Si2O8) contained in lunar regolith. Hydrochloric acid was used as a leaching reagent as it fits within a conceptual circular industrial basis for in situ lunar resource extraction and manufacturing. A laboratory prototype was built, and commercially sourced lunar highland simulant was used to test if the non-anorthite components of the regolith would have a deleterious effect on the process. The process involved a crude beneficiation step, followed by leaching with hot hydrochloric acid (HCl), centrifuge separation, HCl sparging, and double calcination of the final product. While silica was produced from the initial leaching, aluminium chloride hexahydrate (AlCl3·6H2O) was precipitated from the sparged supernatant. The hexahydrate was then double calcined to produce the final alumina product. The silica and alumina that was produced could be used for the production of neutral refractory ceramics and fused silica glass, and thermal insulation fibers. By further reducing the alumina using an electrochemical, such as the metalysis FFC process, the alumina could produce pure aluminium metal with oxygen gas as a by-product. As for the silica produced, putting the product through a molten rock electrolysis process could produce higher purity silicon for use in early stage in situ photovoltaic cell production. The findings of our research demonstrated that the regolith was a good candidate for HCl leaching and the method used would make for a good candidate for lunar resource extraction using minimal Earth-sourced reagents. Overall, our research demonstrated an avenue for in situ extraction of base materials of establish a manufacturing base on the Moon using locally sourced feedstock and minimal Earth-sourced reagents. Future research will use the lessons learned from the experiment in proposing methods of automating and optimizing the extraction process and more focus will be put on the development of physical beneficiation of the regolith to improve the quality of the extracted materials. The process used in this research produces no toxic byproducts and fits well within a near-circular industrial ecosystem where the reagents and unused products are recycled and used to carry out other extraction reactions. As we return to the Moon and plan a sustained presence there, it is critical that we approach lunar industrialization in a sustainable manner.