Dissolution Chemistry of Minnesota Lunar Simulant 932243
Conversion of lunar regolith into a plant growth medium is crucial to the development of a regenerative life support system for a lunar base. Plants, which are the core of such a system, are a source of food and oxygen for humans and a sink for carbon dioxide and other wastes. Because of the the shortage of lunar regolith, simulants were used for examining its suitability for plant growth.
Dissolution studies of Minnesota Lunar Simulant (MLS), a prepared finely-ground basalt, were conducted to measure solution species, to assess the levels of plant nutrients and toxic elements, and to identify the minerals controlling these levels. MLS weathered in shaker flasks over a 150 d period yielded basic solutions of pH near 9.0 buffered by calcite. Most elemental concentrations were within the range for typical alkaline terrestrial soil solutions. Magnesium, sulfur, and sodium concentrations were slightly elevated, and the molybdenum content was high since its content in the MLS is much greater than that for lunar regolith.
Many of the plant nutrients in MLS solution (Mg, S, K, Ca, CI, Mo, P, B, Ni, and Cu) were at concentrations acceptable for plant growth. Nitrogen, however, was deficient. DTPA test results indicate that manganese was deficient, too, and that extractable iron and zinc levels after 150 d were marginal. The solution concentrations of metals were several orders of magnitude below those which are toxic to plants. Nickel and chromium were present at relatively constant concentrations less than 0.05 ppm over the entire weathering cycle. Aluminum hydroxide, calcite, and clinoenstatite were found to be the most likely mineral controls for aluminum, calcium, and magnesium, respectively. Many of the methods used are applicable to studies of actual lunar regolith.