Cesium migration in Hanford sediment: a multisite cation exchange model based on laboratory transport experiments

Steefel, Carl I.; Carroll, Susan A.; Zhao, Pihong; Roberts, Sarah

doi:10.1016/s0169-7722(03)00033-0

Cited by 151 publications

(179 citation statements)

References 43 publications

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“…Both mineral dissolution and precipitation were considered, although in general the low pH of the solution prevented supersaturation of any common possible secondary phases. In addition, cation exchange was considered by introducing a bulk cation exchange capacity of 120 micro-equivalents per gram sediment, a reasonable value for a sediment containing moderate amounts of clay (Steefel et al, 2003).…”

Section: Core Flood Experimentsmentioning

confidence: 99%

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

Beckingham

Steefel

Swift

et al. 2017

Geochimica et Cosmochimica Acta

121

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The rates of mineral dissolution reactions in porous media are difficult to predict, in part because of a lack of understanding of mineral reactive surface area in natural porous media. Common estimates of mineral reactive surface area used in reactive transport models for porous media are typically ad hoc and often based on average grain size, increased to account for surface roughness or decreased by several orders of magnitude to account for reduced surface reactivity of field as opposed to laboratory samples. In this study, accessible mineral surface areas are determined for a sample from the reservoir formation at the Nagaoka pilot CO2 injection site (Japan) using a multi-scale image analysis based on synchrotron Xray microCT, SEMQEMSCAN, XRD, SANS, and FIB-SEM. This analysis not only accounts for accessibility of mineral surfaces to macro-pores, but also accessibility through connected micro-pores in smectite, the most abundant clay mineral in this sample. While the imaging analysis reveals that most of the micro-and macro-pores are well connected, some pore regions are unconnected and thus inaccessible to fluid flow and diffusion. To evaluate whether mineral accessible surface area accurately reflects reactive surface area a flow-through core experiment is performed and modeled at the continuum scale. The core experiment is performed under conditions replicating the pilot site and the evolution of effluent solutes in the aqueous phase is tracked.Various reactive surface area models are evaluated for their ability to capture the observed effluent chemistry, beginning with parameter values determined as a best fit to a disaggregated sediment experiment (Beckingham et al., 2016) described previously.Simulations that assume that all mineral surfaces are accessible (as in the disaggregated sediment experiment) over-predict the observed mineral reaction rates, suggesting that a reduction of RSA by a factor of 10-20 is required to match the core flood experimental data. While the fit of the effluent chemistry (and inferred mineral dissolution rates) greatly improve when the pore-accessible mineral surface areas are used, it was also necessary to include highly reactive glass phases to match the experimental observations, in agreement with conclusions from the disaggregated sediment experiment. It is hypothesized here that the 10-20 reduction in reactive surface areas based on the limited pore accessibility of reactive phases in core flood experiment may be reasonable for poorly sorted and cemented sediments like those at the Nagaoka site, although this reflects pore rather than larger scale heterogeneity.

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Section: Core Flood Experimentsmentioning

confidence: 99%

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

Beckingham

Steefel

Swift

et al. 2017

Geochimica et Cosmochimica Acta

121

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“…Of the 149 single shell tanks, approximately 65 to 70 have been diagnosed as having released HLRW to the subsurface either from loss of tank integrity or from pipes used during transfers into and out of the tanks [8]. Various aspects of the acute effects of the released HLRW on sediments, including mineral weathering and contaminant transport have been extensively investigated [9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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

Chang

Rod

et al. 2011

Environ. Sci. Technol.

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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

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“…Principal radionuclide contaminants at the Hanford Site- 137 Cs, 90 Sr, and 129 I-have markedly different reactive transport behaviors influenced by the chemical composition of the waste solution and its interaction with the solid phase (6,9,13,14). Hyperalkaline, high ionic-strength waste solutions can induce rapid, incongruent sediment weathering reactions that dramatically alter contaminant sequestration (5,10,(15)(16)(17).…”

Section: Introductionmentioning

confidence: 99%

Contaminant Desorption during Long-Term Leaching of Hydroxide-Weathered Hanford Sediments

Thompson

Steefel

Perdrial

et al. 2010

Environ. Sci. Technol.

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BRIEF:Leaching waste-altered Hanford sediments with neutral solutions desorbs Sr from de novo waste-generated minerals and desorbs Cs from high-affinity ion exchange sites. 2 ABSTRACTMineral sorption/co-precipitation is thought to be a principal sequestration mechanism for radioactive 90 Sr and 137 Cs in sediments impacted by hyperalkaline, high-level radioactive waste (HLRW) at the DOE's Hanford Site. However, the long-term persistence of neoformed, contaminant bearing phases after removal of the HLRW source is unknown. We subjected pristine Hanford sediments to hyperalkaline Na-Al-NO 3 -OH solutions containing Sr, Cs, and I at 10 -5 , 10 -5 , and 10 -7 molal, respectively, for 182 days with either <10 ppmv or 385 ppmv pCO 2 . This resulted in the formation of feldspathoid minerals.We leached these weathered sediments with dilute, neutral-pH solutions. After 500 pore volumes (PV), effluent Sr, Cs, NO 3 , Al, Si and pH reached a steady-state with concentrations elevated above those of feedwater. Reactive transport modeling suggests that even after 500 PV, Cs desorption can be explained by ion exchange reactions, whereas Sr desorption is best described by dissolution of Sr-substituted, neo-formed minerals. While, pCO 2 had no effect on Sr or Cs sorption, sediments weathered at <10ppmv pCO 2 did desorb more Sr (66% vs. 28%) and Cs (13% vs. 8%) during leaching than those weathered at 385 ppmv pCO 2 . Thus, the dissolution of neo-formed aluminosilicates may represent a long-term, low-level supply of 90 Sr at the Hanford site.

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Cesium migration in Hanford sediment: a multisite cation exchange model based on laboratory transport experiments

Cited by 151 publications

References 43 publications

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

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

Contaminant Desorption during Long-Term Leaching of Hydroxide-Weathered Hanford Sediments

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