Nanophase iron-enhanced chemical reactivity of ground lunar soil

The plan to resume robotic and manned missions to the Moon in the next decade has led to a renewed interest in the properties of lunar soils, ranging from geological to chemical to toxicological. As an approximation of the effects of crushing and weathering on the Moon, previous work (W. T. Wallace et al. (2009) Meteor. Planet. Sci. 44: 961–970) demonstrated that freshly ground lunar soil is extremely active, as measured by the production of hydroxyl radicals in solution. The present study was performed in order to understand the origin of this reactivity. We have ground 8 lunar soils of varying maturity and source (highland or mare) and measured the hydroxyl-radical production and decay of the reactivity. It was determined that there is a direct correlation between the reactivity and the amount of nanophase metallic iron particles (as a function of soil maturity) in the samples; thus, the highland soils, with their lower total FeO contents, and less nanophase iron, are less reactive than ground mare soils. However, there was no obvious correlation between maturity and source (highland or mare), with respect to the amount of time required for deactivation to a non-reactive state. These results provide the first chemical reactivity values as an important property of lunar soils, necessary data for returning humans to the Moon.