BIOLEACHING OF LUNAR AND MARTIAN PLANETARY SIMULANTS AND ILMENITE IN THE PRESENCE OF IRON-OXIDIZING BACTERIA

The in-situ utilization of resources from other planets, moons, and asteroids will likely be an important component of future space exploration. Traditional techniques that may be used to extract metals like iron, titanium, and aluminum from planetary rocks have large energy and/or hardware requirements that may not be feasible in all cases. In this study, we investigated bioleaching as a possible alternative to high-temperature combustion and reduction techniques for the breakdown of basaltic rocks and ilmenite (FeTiO₃). The objectives of our study were (1) to determine whether the presence of Acidithiobacillus Ferrooxidans, an Fe-oxidizing bacterial strain, increased leaching rates, and (2) to determine whether the bacteria could grow on the low concentrations of ferrous Fe generated by the available substrates. Experimental results demonstrated that more Fe was leached from ilmenite (FeTiO₃) and a lower pH was maintained in the presence of Fe-oxidizing bacteria than compared to abiotic control experiments. This suggests that the bacteria were able to grow using the ferrous iron from ilmenite (and a metal-free growth media) as a substrate. Elemental release rates for basaltic rock types also increased slightly over abiotic controls in the presence of A. Ferrooxidans. For example, leaching of JSC-Mars-1A simulant with the bacteria released Si at a rate of 6.6e^-12 mol/m²*s, while Si leached from the abiotic control at a rate of 4.0e^-12mol/m²*s. Blending of the Mars-1A simulant with ilmenite to further stimulate Fe oxidation by providing additional ferrous iron resulted in a Si release rate of 6.9e^-12 mol/m²*s. These initial results suggest that A. Ferrooxidans might be used to assist in the leaching of rocks and minerals that have only modest concentration of ferrous Fe. Moreover, similar results may be possible using anaerobic strains of Fe-oxidizing bacteria that utilize nitrate as an oxidant. Finally, this study suggests that under the right conditions, energy from the Fe(II)/Fe(III) redox couple might be able to support bacterial life on other planets.