HR: 14:50h
AN: H23H-05    [Abstracts]
TI: Colloid Formation and Transport at Waste Plume Fronts
AU: * Wan, J
EM: jwan@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd. MS 70-108, Berkeley, CA 94720 United States
AU: Tokunaga, T K
EM: tktokunaga@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd. MS 70-108, Berkeley, CA 94720 United States
AU: Larsen, J T
EM: jtlarsen@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd. MS 70-108, Berkeley, CA 94720 United States
AU: Zheng, Z
EM: ZZheng@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Rd. MS 70-108, Berkeley, CA 94720 United States
AB: We have recently identified the phenomenon of massive colloid formation and transport within moving waste plume fronts during infiltration of high-salinity waste solutions into sediments. Colloid formation and transport was thousands of times higher within a narrow zone at the moving plume front than in the plume body and the leaching stage. The newly formed plume front colloids were primarily in the size range from tens of nm to a few micron meters. The underlying process begins with rapid and completed cation exchange of Na+ from the infiltrating waste solution replacing Ca2+ and Mg2+ from the sediments, coupled with flow of the infiltrating waste solution enriched these divalent cations within the moving plume front. Subsequent precipitation of colloids containing these divalent cations released protons and reduced the plume front pH to as low as neutral. This substantially reduced pH in turn promoted precipitation of other pH sensitive minerals and amorphous phases as colloids. This plume front colloid generation phenomenon can occur under a wide range of conditions including sediment type, waste solution pH, temperature, and chemical composition, with the only necessary condition being that of a high ionic strength waste solution. Because of the large mass of suspended colloids generated, this phenomenon could significantly affect the fate and transport of the contaminant trace elements contained within the waste plumes. Depending on the chemical properties of the individual radionuclide or toxic metal, it can co-precipitate with or adsorb onto the plume front colloids. As an example, uranium was predicted and found preferentially precipitated as a mobile colloid phase within a uranium waste plume front. Funding of this research was provided by the Geosciences Research Program of Basic Energy Science, U.S. Department of Energy.
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
DE: 1045 Low-temperature geochemistry
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting