HR: 11:05h
AN: H42C-04    [Abstracts]
TI: Real-Time Colloid Transport Monitoring Using Synchrotron X-ray Diffraction
AU: * Savage, K S
EM: k.savage@vanderbilt.edu
AF: Earth and Environmental Sciences, Vanderbilt University, Station B35-1705, Nashville, TN 37235, United States
AU: Webb, S M
EM: samwebb@slac.stanford.edu
AF: Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, MS-99, Menlo Park, CA 94025, United States
AU: Weinman, B R
EM: beth.weinman@vanderbilt.edu
AF: Earth and Environmental Sciences, Vanderbilt University, Station B35-1705, Nashville, TN 37235, United States
AU: Covey, A K
EM: aaron.k.covey@vanderiblt.edu
AF: Earth and Environmental Sciences, Vanderbilt University, Station B35-1705, Nashville, TN 37235, United States
AB: We investigated the mobility of freshly prepared and aged ferrihydrite colloids through sequentially encountered porous matrices with contrasting isoelectric points, quartz and calcite sands. Influent solutions varied in suspension density, arsenate concentration and pH. X-ray diffraction was performed on 1mm ID plasticrit columns mounted on an electronically controlled mobile sample stage as solutions were pumped or pushed through the columns. Two-dimensional diffraction patterns were repeatedly collected at 4-5 points along the column over the course of several hours. Colloid suspensions and the coarse matrix materials produce different characteristic diffraction patterns. The small size and numerous crystallites of colloids leads to the production of a small angle scattering peak (SASP) and/or uniform Bragg cones, recorded on an image plate detector as rings, whereas the larger matrix grains produce oriented Bragg reflections, recorded as spots or short arcs. Consequently, the appearance of the SASP or rings in the otherwise spotted diffraction pattern provides time- resolved visual evidence for accumulation of colloids at different locations in matrix. Colloid accumulation in calcite sand or in quartz sand is consistent with predictions from electrostatic considerations. This technique provides a new approach for monitoring colloid transport in real time, and identifying where colloids accumulate in heterogeneous porous media.
DE: 1030 Geochemical cycles (0330)
DE: 1094 Instruments and techniques
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2007 Fall Meeting