Strontium and Cesium Release Mechanisms during Unsaturated Flow through Waste-Weathered Hanford Sediments

Abstract

TitleStrontium and cesium release mechanisms during unsaturated flow through wasteweathered Hanford sediments Cs. The mineral composition of the weathered sediments showed that zeolite (chabazite-type) and feldspathoid (sodalitetype) were the major byproducts but different contents depending on the weathering conditions.Reactive transport modeling indicated that Cs leaching was controlled by ion-exchange, while Sr release was affected primarily by dissolution of the secondary minerals. The later release of K, Al, and Si from the HI-column indicated the additional dissolution of a more crystalline mineral (cancrinite-type). A two-site ion-exchange model successfully simulated the Cs release from the LO-column. However, a three-site ion-exchange model was needed for the HI-column. The study implied that the weathering conditions greatly impact the speciation of the secondary minerals and leaching behavior of sequestrated Sr and Cs.3

Alteration, adsorption and nucleation processes on clay–water interfaces: Mechanisms for the retention of uranium by altered clay surfaces on the nanometer scale

“…In this regard, experimental studies explored clay alteration and formation of new phases with different swelling and adsorption properties under conditions expected to occur within a Nuclear Waste repository or in the subsurface of the Hanford site. In the latter location, highly alkaline waste solutions leached from storage tanks are now in contact with clay-bearing sediments in the subsurface (Chorover et al, 2003(Chorover et al, , 2008Zhao et al, 2004;Choi et al, 2005a,b;Crosson et al, 2006;Chang et al, 2011;Perdrial et al, 2011). In a potential Nuclear Waste repository with a multi-barrier system of bentonite buffers, steel canisters and concrete overpacks, alkaline pore waters may also form through dissolution of the concrete and oxidation of metallic Fe.…”

“…Studies simulating the interaction of Hanford tank waste solution with clay minerals (Na-Al-NO 3 -system with pH values P12) identified for example illite, the feldspathoids cancrinite, sodalite and the zeolites chabazite and X as alteration products of kaolinite, illite, vermiculite and montmorillonite (Chorover et al, 2003;Zhao et al, 2004;Crosson et al, 2006;Chang et al, 2011). Studies further indicated enhanced uptake and incorporation of Sr, Cs and I (representing the radionuclides 90 Sr, 137 Cs and 129 I) by feldspathoids and zeolites relative to the unaltered clays (Chorover et al, 2003(Chorover et al, , 2008Choi et al, 2005a,b;Perdrial et al, 2011).…”

Injectable Apatite for the Sequestration of Sr-90 in Groundwater

“…The source solution was pumped through the columns using a peristaltic pump (Ismatec 78001-02) at desired flow rates (1 mL/min for column 1 and most of time for column 2 and 1.85 mL/min between day 26 to day 27 for phase II of column 2) ( Table 2). In phase III of column 2, the source solution was switched from the Ca-citrate-phosphate solution to the uncontaminated groundwater (Table 3), obtained from the same site where the sediment was collected, after spiked with 1 mg/L Sr (stable Sr as a surrogate for Sr-90 (Rabideau et al, 2005;Chang et al, 2011)) ( Table 2). All source solutions were supplied to the columns as continuous injection systems.…”

Mineral dissolution and secondary precipitation on quartz sand in simulated Hanford tank solutions affecting subsurface porosity

“…Contact of the released hyperalkaline tank fluid with the underlying sediments has caused geochemical changes, resulting in primary mineral dissolution and precipitation of secondary minerals (Bickmore et al, 2001;Chorover et al, 2003Chorover et al, , 2008Qafoku et al, 2003;Mashal et al, 2004;Zhao et al, 2004;Deng et al, 2006a,b;Rod et al, 2010;Chang et al, 2011). The caustic tank leachate dissolves silicate minerals and the released Si can react with Al, Na, and anions such as NO À 3 ; CO 2À 3 , or OH À from tank wastes to form secondary mineral precipitates.…”

“…However, in general, crystalline feldspathoids such as sodalite and cancrinite [Na 8 Si 6 Al 6 O 24 (NO 3 ) 2 ] can be formed at temperatures above 40°C and at high NaOH (>1 M) solutions (Bickmore et al, 2001;Mattigod et al, 2002;Qafoku et al, 2003;Mashal et al, 2004;Deng et al, 2006a). Compared to the primary minerals, these neo-formed secondary minerals demonstrate elevated sorption capacity resulting from increased surface adsorption and co-precipitation of radionuclides such as Sr and Cs (Chorover et al, 2003;Mon et al, 2005;Um et al, 2005;Choi et al, 2006;Rod et al, 2010;Chang et al, 2011).…”