Feasibility studies for hydrogen reduction of ilmenite in a static system for use as an ISRU demonstration on the lunar surface

摘要

The ESA-ROSCOSMOS mission, Luna-27, scheduled for launch in 2023, includes a payload known as PROSPECT that is intended for sampling the polar lunar regolith through drilling, with subsequent analyses of the retrieved material. One of the aims of the analytical module, ProSPA, which is being developed at The Open University, is to identify and quantify the volatiles present in the extracted sample that are released by heating from ambient up to 1000 degrees C and analyzed by the mass spectrometers to assess their potential for in-situ resource utilization. The ProSPA design also includes a provision to test the extraction of water (and its associated oxygen) from lunar regolith by hydrogen reduction. Previous attempts at such extractions generally utilize a flow of hydrogen gas through the feedstock to efficiently extract water. However, in ProSPA, samples would be processed in a static mode, which leads to concerns that the reaction may be suppressed by inefficient removal of water vapor above the regolith. A first order theoretical assessment of the diffusion of gases in such a system was performed and suggested that water can diffuse through the system at an acceptable rate and be collected upon a cold finger thus enabling the reaction to proceed. Proof of concept experiments were successfully performed with a ProSPA breadboard using ilmenite samples up to similar to 45 mg heated at 900 degrees C for 60 min. Subsequent heating of the cold finger, in vacuum, released 17 +/- 1 mu mol water from a 44.7 +/- 0.5 mg sample, equating to a calculated yield of 0.6 +/- 0.1 wt % oxygen, and a reduction extent of 5.8 +/- 0.4%. A sample of mass 11.2 +/- 0.5 mg had the greatest calculated yield of 1.4 +/- 0.2 wt % oxygen, and this equates to a reduction extent of 12.9 +/- 1.5%. SEM analyses of cross-sections of grains showed evidence of a reduction reaction inside the ilmenite grains with some showing greater reduction than others, indicating the reaction is limited by furnace dimensions, reaction kinetics and geometry. The results suggest that the ProSPA ISRU experiment should be capable of producing water, and therefore oxygen, by hydrogen reduction of ilmenite, ultimately this could be a viable technique for producing oxygen from ilmenite-containing lunar regolith with ProSPA.