title: Linking cesium and strontium uptake to kaolinite weathering in simulated tank waste leachate.
abstract: Weathering behavior of kaolinite was studied in batch systems under geochemical conditions characteristic of tank waste released to the vadose zone at the Hanford Site, WA (0.05 M Al(T), 2 M Na+, 1 M N03-, pH approximately 14, Cs+ and Sr2+ present as co-contaminants). Time series experiments were conducted from 0 to 369 d, with initial Cs+ and Sr2+ concentrations ranging from 10(-5) to 10(-3) M. Dissolution of kaolinite increased soluble Si and Al to maximum levels at 7 d (Cs and Sr concentrations of 10(-5) and 10(-4) M) or 33 d (Cs and Sr concentrations of 10(-3) M). Subsequent precipitation of Si and Al was coupled to the formation of oxalate-extractable solids that incorporated Cs and Sr. Strontium sorption was nearly complete within 24 h for initial Sr concentrations (Sr0) < or = 10(-4) whereas Cs uptake increased over the full year of the experiment for all initial Cs concentrations. Spectroscopic analyses revealed neoformed solids including the zeolite Na-Al silicate (Al-chabazite), and feldspathoids sodium aluminum nitrate silicate (NO3-sodalite), and sodium aluminum nitrate silicate hydrate (NO3-cancrinite), which can incorporate Cs. Single-pulse 27Al solid-state nuclear magnetic resonance (NMR) spectroscopyyielded first-order rate constants (k)for mineral transformation that decreased from 3.5 x 10(-3) to 2 x 10(-3) d(-1) as Cs and Sr concentrations were increased from 10(-5) to 10(-3) M. Discrete strontium silicate solids were also observed. The incongruent dissolution of kaolinite promoted the sequestration of contaminants into increasingly recalcitrant solid phases over the 1-yr time period.
authors.affiliation: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona 85721, USA. chorover@cals.arizona.edu
authors.forename: Jon
authors.initials: J
authors.lastname: Chorover
authors.forename: Sunkyung
authors.initials: S
authors.lastname: Choi
authors.forename: Mary Kay
authors.initials: MK
authors.lastname: Amistadi
authors.forename: K G
authors.initials: KG
authors.lastname: Karthikeyan
authors.forename: Garry
authors.initials: G
authors.lastname: Crosson
authors.forename: Karl T
authors.initials: KT
authors.lastname: Mueller
mesh_terms: D000327:Adsorption; D002586:Cesium / Q000032:analysis*; D007616:Kaolin / Q000737:chemistry*; D008956:Models, Chemical; D011848:Radioactive Pollutants / Q000032:analysis*; D011850:Radioactive Waste / Q000517:prevention & control*; D012037:Refuse Disposal / Q000379:methods*; D012995:Solubility; D013324:Strontium / Q000032:analysis*; D014861:Washington; D014887:Weather
chemical_list: D011848:Radioactive Pollutants; D011850:Radioactive Waste; D002586:Cesium; D007616:Kaolin; D013324:Strontium