The Technology Transfer and Partnerships Office
Metals from Regolith

Metals are typically found in planetary rocks and soils in the form of oxides and in rare occasion in elemental form such as iron particles in lunar regolith. Since the extraction of oxygen from minerals involves splitting the oxide molecules, metals are typically co-produced in oxygen extracting technologies for ISRU. Their production is equally important for long-term presence on planetary surfaces and the safety of human crews far from Earth. In fact, developing the ability to use metals produced in situ as raw material to fabricate spacecraft parts or to make repairs is a logical step in our journey of exploration in space. Six metals comprise the majority of the oxides in lunar material: Si, Al, Ti, Fe, Mg, and Ca. The remarkable advances in global data collection of the lunar surface by Clementine, Lunar Prospector and Moon Mineralogical Mapper and now Lunar Reconnaissance Orbiter reveal how metal concentrations vary across the lunar surface. Their respective abundances vary significantly by location, mineralogy and even by grain size in regolith. These variations constitute a significant challenge for extraction technologies that must be flexible enough to reduce a variety of metal oxides with similar efficiencies to make metal production feasible.



Global map of the iron concentration on the lunar surface

Global map of the iron concentration on the lunar surface created from data collected by the Clementine mission. Colors represent 2% increments of increasing FeO concentration from black (0%) to white (16%). (Source: NASA/Clementine)



in lunar samples
Microscopic Imager images (each 3cm across) obtained by Mars rovers at Gusev and Meridiani craters. The variability in textures, physical properties and compositions is important to develop extraction technologies for Mars. Images: a. and e. Bright dust (nanophase ferric oxides); b. and f. dark soils (low sulfur, iron concentrations up to 38%); c. bedform armour (enhanced in Fe, Ca, Cr, and Br); d. rounded pebbles in matrix of surface dust; g. haematitic spherules on dark soil (rich in Fe, Ni); h. sub-angular, vesicular clasts on dark soil. (Image credit: NASA/JPL/Mars rovers)

Much less is known today of the concentrations of metals in the Martian soils and rocks. This picture is changing thanks to the analysis of Mossbauer data collected by the Mars rovers Spirit and Opportunity and the correlations made with remote sensing by Mars Global Surveyor and Odyssey and the on-going mineral mapping by ESA’s Mars Express. Martian surface materials display some of the diversity in composition, mineralogy and locality that terrestrial materials do because water and volcanism seem to have played a major role there too. These forces weather the minerals and materials bearing concentrations of iron, silicon, magnesium, and titanium are found in the form of metal oxides and metal sulfates. The presence of chlorine and bromine at significant levels also will dictate the development of different extraction technologies for metals on Mars.


The production of metals must also yield these products in useful form just as it is done in commercial production on Earth. The use of these metals in ISRU eventually dictate how they should produce; a metal produced in its solid state may be suitable for cold fabrication techniques such as cutting, grinding while metal produced as melts (liquid state) can be flowed out of a reactor to be cast into molds or formed during cooling. As a consequence, some technologies that are well suited to extract oxygen from metal oxides also produce these metals while leaving them embedded in the mineral by-products. For these reasons, the ISRU Technology Development Project has focused on two metal extraction technologies:

Molten Regolith Electrolysis
Carbothermic Reduction of Regolith

References:

An Integrated View of the Chemistry and Mineralogy of Martian Soils, A.S. Yen et al., Nature 436, 49-54 (2005).