HR: 1340h
AN: V43B-1582    [Abstracts]
TI: Cation Exchange Reactions Controlling Desorption of ⁹⁰Sr²⁺ From Coarse-Grained Contaminated Sediments at the Hanford Site, Washington
AU: * McKinley, J P
EM: james.mckinley@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, msK8-96, Richland, WA 99354 United States
AU: Zachara, J M
EM: john.zachara@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, msK8-96, Richland, WA 99354 United States
AU: Smith, S C
EM: steven.smith@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, msK8-96, Richland, WA 99354 United States
AU: Liu, C
EM: chongxuan.liu@pnl.gov
AF: Pacific Northwest National Laboratory, PO Box 999, msK8-96, Richland, WA 99354 United States
AB: Nuclear waste that bore ⁹⁰Sr²⁺ was accidentally leaked into the vadose zone at the Hanford site, and was immobilized at relatively shallow depths in sediments containing little apparent clay or silt-sized components. We desorbed Sr²⁺, ⁹⁰Sr²⁺, Mg²⁺, and Ca²⁺, and monitored total inorganic carbon concentration during the equilibration of this sediment with varying concentrations of Na⁺ and Ca²⁺. A cation exchange model previously developed for similar sediments was applied to these results as a predictor of final solution compositions. The model included binary exchange reactions for the four operant cations and an equilibrium dissolution/precipitation reaction for calcite. The model produced an excellent prediction for desorption data. We also examined the contaminated sediment using digital autoradiography, a sensitive tool for imaging the distribution of radioactivity. The exchanger phase containing ⁹⁰Sr was found to consist of smectite formed from weathering of mesostasis glass in basaltic lithic fragments. These clasts are a significant component of Hanford formation sands. The relatively small but significant cation exchange capacity of these sediments was thus a consequence of reaction with physically sequestered clays in a sediment that contained essentially no fine-grained material. The nature of this exchange component explains the relatively slow (scale of days) evolution of desorption solutions. The experimental and model results indicate that there is little risk of migration of ⁹⁰Sr²⁺ to the water table.
DE: 1065 Major and trace element geochemistry
DE: 1090 Field relationships (3690, 8486)
DE: 1831 Groundwater quality
DE: 1875 Vadose zone
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005