HR: 0800h
AN: H11E-0340    [Abstracts]
TI: Engineered Calcite Precipitation in Porous Media: Effects on Flow and Vice Versa
AU: * Fujita, Y
EM: fujiy@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Delwiche, M E
EM: mde1@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Schafer, A L
EM: nsa@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: White, T A
EM: whitta@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Versteeg, R J
EM: versrj@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AU: Smith, R W
EM: smithbob@uidaho.edu
AF: University of Idaho-Idaho Falls, 1776 Science Center Dr., Idaho Falls, ID 83402 United States
AU: Redden, G D
EM: reddgd@inel.gov
AF: Idaho National Engineering and Environmental Laboratory, P. O. Box 1625, Idaho Falls, ID 83415 United States
AB: Engineered precipitation of minerals in the subsurface offers a potential means to control the mobility of some trace metal and radionuclide contaminants in groundwater. Examples include biological reduction of U(VI) to insoluble UO$_{2}$, and co-precipitation of $^{90}$Sr and other divalent metals in calcite. In order to take advantage of in situ precipitation in field-scale remediation technologies we must be able to control the onset and distribution of mineral precipitation within a porous medium. This is challenging because precipitation can alter permeability and flow paths. Models predicting the coupling between mineral precipitation, delivery mechanisms, and changes in local flow behavior are not yet well developed, and improved information on mechanistic relationships linking parameters and processes is needed. We are currently conducting laboratory investigations to provide data that will support the development of both improved models for coupling between precipitation and flow, and techniques for monitoring precipitation events in the field. The model experimental system that we are using is calcite precipitation induced by enzymatic hydrolysis of urea to bicarbonate and ammonium, catalyzed by the enzyme urease. Urea hydrolysis thus results in the in situ generation of the reactant (bicarbonate) necessary for calcite precipitation. For these experiments we are using urease immobilized on macroporous EupergitAź’'A,A› C beads mixed with quartz sand and packed within a defined zone in a sand column. Varying the flux of urea and calcium through the urease zone provides a means to affect the distribution and extent of calcite precipitation. Column experiments are underway to test some basic hypotheses related to precipitation as a function of hydrolysis kinetics, precipitation kinetics and flow rates. X-ray tomography and complex resistivity are being tested as methods to monitor and map precipitation within porous media at different scales.
DE: 1829 Groundwater hydrology
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting