| Organic acids from the biosphere are important reactants in a number of weathering environments. Organic acids accelerate silicate dissolution, increase silicate solubility, mobilize aluminum and silica, and alter the equilibrium between the solution and precipitated secondary phases. The chemical dynamics of the weathering environment was examined by investigating the interaction between mineral surfaces and organic/inorganic electrolyte solutions. Organic acids, analogs of microbially generated siderophores, were examined for their effects on aluminosilicate dissolution kinetics at multiple temperatures in various electrolyte solutions.; Mineral surface titrations were performed for six mineral samples: quartz, gibbsite, feldspars, microcline, andalusite, and kyanite. Mineral powder/distilled water mixture samples were titrated by 0.1 N HCl in the basic pH region, and by 0.1 N NaOH in the acidic pH region. UV-difference spectroscopic analysis was performed on dissolved silica-organic acid mixtures to characterize solution complexes. Mineral dissolution experiments were performed using temperature controlled, continuous-flow mixed reactors. For inorganic dissolution experiment, the solution ionic strength was controlled using LiCl while solution pH was adjusted using either dilute HCl or LiOH solutions. Reagent grade citric acid, tropolone, and 3,4-dihydroxybenzoic acid were used for organic ligand dissolution experiments. A constant flow rate was maintained by using a peristaltic proportioning pump.; The mineral surface titration results revealed important surface properties that can be critical to interpreting dissolution kinetics in natural environments. One of the most important results would be that the amount of active surface sites can vary in different solution pH conditions which have been normally assumed to be fixed numbers based on surface area measurements. (Abstract shortened by UMI.)... |
