At Black Mesa, feldspars in the Navajo Sandstone are dissolving at ˜10 5 times slower than laboratory rate at comparable temperature and pH under far from equilibrium condition. These characteristics of the aged feldspar surfaces accentuate the differences in reactivity between the freshly ground feldspar powders used in laboratory experiments and feldspar grains in natural systems, and may partially contribute to the commonly observed apparent laboratory-field dissolution rate discrepancy.
Authigenic K- feldspar overgrowth and etch pits were also found on feldspar grains. Outside of the kaolin coatings, feldspar grains are covered with a continuous 3-5 μm thick layer of authigenic smectite, which also coats quartz and other sediment grains. In addition to the amorphous layer, the feldspar surfaces are also partially coated with tightly adhered kaolin platelets. The amorphous layer is probably deficient in K and enriched in Si. Here, we report the first HRTEM observation of a 10-nm thick amorphous layer on naturally weathered K- feldspar in currently slightly alkaline groundwater. Naturally weathered feldspar surfaces in the Jurassic Navajo Sandstone at Black Mesa, Arizona, was characterized with high-resolution transmission and analytical electron microscope (HRTEM-AEM) and field emission gun scanning electron microscope (FEG-SEM). Naturally weathered feldspar surfaces in the Navajo Sandstone aquifer, Black Mesa, Arizona: Electron microscopic characterization A good efficiency of PCA5 in separation of paraffin oil (a minimum residual turbidity of 9.8%) has been also found. The negative value of the zeta potential and flocs size measurements, at the optimum polymer dose, point to contribution from charge patch mechanism for the particles flocculation.
Except for ZnO, the interactions between PCA5 and suspended particles led to low residual turbidity values (around 4% for kreutzonit, 5% for kaolin and 8% for K- feldspar) as well as to the reduction of flocs settling time (from 1200Â min to 30Â min and 120Â min in case of kaolinit and K- feldspar, respectively), that meant a high efficiency in their separation. The effect of several parameters such as settling time, polymer dose and the pollutant type on the separation efficacy was evaluated and followed by optical density and zeta potential measurements. The flocculation efficiency of a cationic polyelectrolyte with quaternary ammonium salt groups in the backbone, namely PCA5 was evaluated on zirconium silicate (kreutzonit), kaolin, K- feldspar and zinc oxide (ZnO) suspensions prepared either with each pollutant or with their mixture. Cationic polyelectrolyte induced separation of some inorganic contaminants and their mixture (zirconium silicate, kaolin, K- feldspar, zinc oxide) as well as of the paraffin oil from water.
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