Hydrogen sulfide consumption by lunar regolith simulants

Future lunar missions like Artemis plan to collect, transport, store and analyze potentially complex mixtures of frozen volatiles and regolith (Colaprete et al., 2010; Weber et al., 2020). Our efforts discussed here identified potential sample modifications involving reactive volatile-regolith mixtures and have shown lunar regolith simulants consume hydrogen sulfide gas, a potential lunar volatile (Colaprete et al., 2010), in hours. These experiments monitored H 2 S headspace concentrations of volatile-regolith simulant mixtures using gas chromatography/mass spectrometry. Two styles of experiments emulated melted ice-regolith scenarios: (1) regolith in direct contact with the aqueous H 2 S solution and (2) regolith only interacting with H 2 S vapor. When in direct contact, ∼ 0.3 g of JSC-1A consumed 50% of at least 8 × 10 −5 moles of H 2 S (approximately 0.03% by mass) in 7 ± 4 to 39 ± 6 min. The hydrogen sulfide 50% consumption time increased to 17 ± 5 to 105 ± 12 min when the regolith simulant was exposed to only H 2 S vapor. Volatile consumption proceeded to completion, indicating physical separation from melting ice grains is not sufficient to prevent sample modification, and that melting or sublimating ice can contaminate grains throughout an entire sealed container. Activation energies were calculated using Arrhenius plots assuming approximate first order kinetics. Similar activation energies for both aqueous (34.6 ± 6.3 kJ/mol) and gaseous (37.0 ± 4.3 kJ/mol) experiments indicates an aqueous phase in contact with the regolith accelerates H 2 S uptake but does not alter the underlying sorption mechanism. Experiments using another regolith simulant, NU-LHT-4M, also consumed H 2 S( g ), but at a different rate, which suggests regolith composition, grain size, and/or surface area appear to be important parameters when predicting volatile-regolith reactions.