Paper No. 10
Presentation Time: 9:00 AM-6:00 PM
A NEW TECHNIQUE FOR IDENTIFYING COLLOID MINERALOGY IN KARST WATERS: APPLYING ATR-FTIR SPECTROSCOPY AND AFM TO KARST COLLOIDS
MCGUIRE, Molly M., Department of Chemistry, Bucknell University, 1 Dent Drive, Lewisburg, PA 17837 and HERMAN, Ellen K., Department of Geology and Environmental Geosciences, Bucknell University, 1 Dent Drive, Lewisburg, PA 17837, ekh008@bucknell.edu
Many springs and other karst features show a characteristic cloudiness even at low flow. This appearance is usually attributed to fine-grained colloids that remain in the water column regardless of water velocity. The composition and nature of these colloids should play an important role in contaminant transport, but few attempts have been made to characterize this material. Most work to date has analyzed colloidal material using techniques with the potential for significant chemical alteration during sample preparation. The prevalent techniques, based on scanning electron microscopy and energy-dispersive x-ray spectroscopy, also give only elemental composition rather than mineralogy. To address this, we analyze a concentrated aqueous suspension using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The spectrum generated shows the colloid mineralogy as well as the presence or absence of organic material and other potential constituents. To examine colloid morphology and particle size, we employ atomic force microscopy (AFM) which can map the topography of individual mineral grains.
To test this technique, we sampled colloids from Smullton Sinks, a series of karst windows in Centre County, PA, USA, that display cloudiness particularly at low flow. Smullton Sinks is part of a telogenetic karst system that occurs in the Ordovician limestones forming the floor of Brush Valley in the Appalachian Valley and Ridge of central Pennsylvania. The water traveling to Smullton drains clastic ridges of sandstone and shale as well as the limestones of the valley floor, and is usually undersaturated with respect to calcite and dolomite. After concentrating a chilled sample by tangential flow ultrafiltration, the ATR-FTIR spectrum showed quartz and layer silicates dominating the colloidal fraction. No evidence of substantial organic material or carbonate species appeared. These particles are consistent with not only the area draining to Smullton, but also the mineralogy of the larger size fraction collected in suspended and bedload sediment samples. AFM results confirmed that the particles selected for analysis are consistent with quartz and layer silicates.
