title: Effect of temperature on Cs+ sorption and desorption in subsurface sediments at the Hanford Site, U.S.A.
abstract: The effects of temperature on Cs+ sorption and desorption were investigated in subsurface sediments from the U.S. Department of Energy Hanford Site. The site has been contaminated at several locations by the accidental leakage of high-level nuclear waste (HLW) containing 137Cs+. The high temperature of the self-boiling, leaked HLW fluid and the continuous decay of various radionuclides carried by the waste supernatant have resulted in elevated vadose temperatures (currently up to 72 degrees C) below the Hanford S-SX tank farm that have dissipated slowly from the time of leakage (1970). The effect of temperature on Cs+ sorption was evaluated through batch binary Cs(+)-Na+ exchange experiments on pristine sediments, while Cs+ desorption was studied in column experiments using 137Cs(+)-contaminated sediments. Cs+ adsorption generally decreased with increasing temperature, with a more apparent decrease at low aqueous Cs+ concentration (10(-10)-10(-6) mol/L). Cs+ desorption from the contaminated sediments increased with increasing temperature. The results indicated that the free energy of Na(+)-Cs+ exchange on the Hanford sediment had a significant enthalpy component that was estimated to be -17.87 (+/- 2.01) and -4.82 (+/- 0.44) kJ/mol (at 298 degrees C) for the high- and low-affinity exchange sites, respectively. Both Cs+ adsorption and desorption at elevated temperature could be well simulated by a two-site ion exchange model, with the conditional exchange constants corrected by the exchange enthalpy effect. The effect of temperature on Cs+ desorption kinetics was also evaluated using a stop-flow technique. The kinetics of desorption of the exchangeable pool (which was less than the total adsorbed concentration) were found to be rapid under the conditions studied.
authors.affiliation: Pacific Northwest National Laboratory, Richland, Washington 99352, USA. chongxuan.liu@pnl.gov
authors.forename: Chongxuan
authors.initials: C
authors.lastname: Liu
authors.forename: John M
authors.initials: JM
authors.lastname: Zachara
authors.forename: Odeta
authors.initials: O
authors.lastname: Qafoku
authors.forename: Steve C
authors.initials: SC
authors.lastname: Smith
mesh_terms: D000327:Adsorption; D002586:Cesium / Q000032:analysis*; D002588:Cesium Radioisotopes / Q000032:analysis*; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry; D006358:Hot Temperature; D011850:Radioactive Waste / Q000032:analysis*; D012990:Soil Pollutants, Radioactive / Q000032:analysis; D013696:Temperature; D014861:Washington; D014875:Water Pollutants, Radioactive / Q000032:analysis
chemical_list: D002588:Cesium Radioisotopes; D011850:Radioactive Waste; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive; D002586:Cesium