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Characterization of Complex Mineral Assemblages: Implications for Contaminant Transport and Environmental Remediation
Pages 3350-3357

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From page 3350...
... The surface charging mechanisms operative in the complex mineral assemblages cannot be predicted based on bulk mineralogy or by considering surface reactivity of less abundant mineral phases based on results from model systems. The fragile nature of mineral assemblages isolated from natural systems requires novel techniques and experimental approaches for investigating their surface chemistry and reactivity free of artifacts.
From page 3351...
... The complex nature of the electrostatic and van der Waals interactions between fine-grained crystalline and poorly ordered phases with mixed surfacecharge properties has hampered the development of suitable models to represent surface reactive functional groups in mixed mineral assemblages. Adsorption studies using binary mixtures of model mineral phases have demonstrated remarkable complexity, with adsorption generally being very poorly predicted by considering a weighted sum of individual mineral components (1, 28~.
From page 3352...
... Recent evidence has indicated that mobile colloids comprised of minerals and complex mineral assemblages can be generated via dispersion processes and transported through many soils and groundwater systems with relatively minor changes in solute chemistry of the invading fluid, thereby avoiding the serious artifacts typically encountered in the isolation of complex mineral assemblages. Mineralogy and Surface Chemistry of Complex Mineral Assemblages Isolated From Soils and Aquifer Materials Although several studies have demonstrated the enhanced mobility of contaminants in the presence of mobile colloids, far fewer have focused on characterizing the mineralogical composition and surface charge properties of the mineral and organic-mineral assemblages comprising the mobile phase.
From page 3353...
... Examination of the mobile colloids by transmission electron microscopy (EM) and selected area electron diffraction reveals that they are comprised primarily of aggregates of microcrystalline Al-substituted goethite along with complex mineral assemblages of goethite-armored kaolinite and crandallite (Ca Al3tPO432~0H]
From page 3354...
... complex mineral aggregates generated during reactive transport experiments when repeatedly analyzed by laser doppler velocimetry: (a) initial mobility distribution, (b)
From page 3355...
... Surface Chemistry of Mixed Mineral Assemblages and the Implication for Solute Transport Surface charge reversal of reactive mineral phases according to the proposed model should be manifested in the reactive transport behavior of anionic solutes. This phenomenon was examined by investigating Br- breakthrough behavior in additional dynamic transport experiments.
From page 3356...
... Most reactive transport modeling efforts define reactive mineral phases based on the relative abundance of the clay minerals present and surface chemistry defined by studies with model minerals. That the surface chemistry of reactive phases in aquifers may be controlled by minerals of relatively low abundance and more importantly, by complex physicochemical interactions occurring between individual components in complex mineral assemblages, suggests that we need less emphasis on studies of model minerals and more research on mineral assemblages isolated from natural systems.
From page 3357...
... (1989) Minerals in Soil Envi ronments (Soil Science Soc.


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