Quantitative and qualitative analysis of highly weathered clays

In my first study, a general curve-fitting program for non-linear functions was used to evaluate the utility of decomposing XRD and TA data from highly weathered soil (HWS) systems for improved mineral quantification. Six pedons from the Piedmont and Coastal Plain physiographic provinces of Alabama were described, sampled by horizon, and characterized. Samples were digested and elemental constituents quantified. Decomposed XRD and TA data were used to improve identification and quantification of minerals. Results showed that decomposition enabled us to more accurately determine mineral percentages for kaolinite, hydroxyl-interlayered vermiculite (HIV), gibbsite, goethite, and quartz. Total mineral recovery estimates were improved compared to traditional quantification by 12% (100% vs. 88%). Final estimates for kaolinite, gibbsite, and quartz were combined with total elemental data to estimate percentages and calculate a structural formula for HIV.; My second study used the improved mineral quantities and the calculated structural formula for HIV to evaluate the stability and weathering relationships in our HWS systems. Soil solutions were extracted using centrifugation, ion activities were calculated, and stability diagrams developed. A standard free energy of formation (ΔGo_f) and a solubility product (pk) for HIV were calculated. Solubility products for surface (Ap) horizons indicated that HIV formation was favored over kaolinite. Stability diagrams showed that most surface (Ap) horizons were supersaturated with respect to HIV gibbsite, and kaolinite. All argillic (Bt) and C subsoil horizons were under-saturated with respect to HIV and gibbsite, indicating the relative stability of kaolinite. Results suggest that mineral stability relationships developed using thermodynamics mimics mineralogical depth trends.; The final study used decomposition with glancing incident X-ray diffraction (GIXD). Glancing incidence X-ray diffraction (GIXD) may improve quantitative efforts using XRD compared to conventional because of increased peak intensity and reduction of substrate scatter. Eighteen XRD samples were evaluated using both traditional Bragg-Brentano X-ray diffraction (BBXD) geometry and GIXD. All XRD patterns were decomposed into individual peaks. Peak intensity, lorentz-polarization, and background noise were three times higher in the GIXD samples. Peak heights, areas, and the full width at-half-the-peak maximum (FWHM) were evaluated in hopes of improving quartz and HIV quantification. Compared with ratios developed from decomposed BBXD patterns, results showed an averaged improved quantification (5%) for (HIV) (RMSE = 25.8 vs. 34.0), but not for quartz. (Abstract shortened by UMI.)...