MINERALOGY, CHEMICAL-COMPOSITION, AND INTERACTION OF LUNAR SIMULANTS WITH HUMIC ACIDS

An investigation was conducted on the mineralogy, chemical composition , and interaction of two NASA lunar simulants, Minnesota basalt and Co ming glass, with humic acid (HA). Chemical composition was determined by a fluoro-boric acid digestion process. Mineral composition was inve stigated by x-ray diffraction analysis (XRD), scanning electron micros copy (SEM), and energy dispersive analysis by x-rays (EDAX). Interacti on was studied by shaking samples of the lunar simulants with HA solut ions at pH 2.45 and 7.0 for 1 to 40 days. Silica, Fe, and Al released were determined by atomic absorption spectroscopy. Changes in mineral structure and elemental composition of single crystals were examined b y SEM and EDAX. Minnesota basalt was composed of approximately 60% pla gioclase and 40% ferromagnesian minerals. The presence of ilmenite was detected by SEM and EDAX. Corning glass was amorphous to XRD. The rat e and kinetics of dissolution of the two lunar simulants were similar to those reported for soil silicates and carbonate minerals. The relea se of Si, Al, and Fe was curvi-linear in regression, and the rate of d issolution was greater at low than at high pH. Interaction with HA res ulted in crust formation covering the lunar mineral surfaces, which ac ted as a barrier, slowing down further dissolution with time. The conc entrations of the dissolved metals were too small to create toxicity i n plants, especially in the presence of HA with its high complexation capacity. If these lunar simulants are considered representative of th e real lunar regolith, it is expected that the interaction between lun ar minerals and soil organic matter will be similar as that between so il minerals and organic matter.