Resupply mechanism to a contaminated aquifer: A laboratory study of U(VI) desorption from capillary fringe sediments

Um, Wooyong; Zachara, John M.; Liu, Chongxuan; Moore, Dean A.; Rod, Kenton A.

doi:10.1016/j.gca.2010.02.001

Cited by 22 publications

(25 citation statements)

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“…6L-Fh was included because a small amount of poorly crystalline Fe(III) oxide exists in the sediment Um et al, 2008Um et al, , 2010. Ferrihydrite displays high affinity for U(VI) over broad pH range (Hsi and Langmuir, 1985;Waite et al, 1994) and has been implicated as a U adsorbent in Hanford sediments (Barnett et al, 2002).…”

Section: Reference Phasesmentioning

confidence: 99%

“…) are common (Bond et al, 2008;Um et al, 2010). Many spectroscopic techniques that are capable of revealing U speciation in mineral materials, such as extended X-ray absorption fine structure (EXAFS) (Hudson et al, 1999;Elzinga et al, 2004), Fourier-transfer infrared spectroscopy (FTIR) (Bargar et al, 1999), and Raman spectroscopy , suffer from low sensitivity and are unable to produce data with satisfactory quality at commonly observed environmental concentrations.…”

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confidence: 99%

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Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: A fluorescence spectroscopy study

Wang

Zachara

Boily

et al. 2011

Geochimica et Cosmochimica Acta

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The adsorption and speciation of U(VI) was investigated on contaminated, fine grained sediment materials from the Hanford 300 area (SPP1 GWF) in simulated groundwater using cryogenic laser-induced U(VI) fluorescence spectroscopy combined with chemometric analysis. A series of reference minerals (montmorillonite, illite, Michigan chlorite, North Carolina chlorite, California clinochlore, quartz and synthetic 6-line ferrihydrite) was used for comparison that represents the mineralogical constituents of SPP1 GWF. Surface area-normalized K d values were measured at U(VI) concentrations of 5 Â 10 À7 and 5 Â 10 À6 mol L À1 that displayed the following affinity series: 6-line-ferrihydrite > North Carolina chlorite % California clinochlore > quartz % Michigan chlorite > illite > montmorillonite. Both time-resolved spectra and asynchronous twodimensional (2D) correlation analysis of SPP1 GWF at different delay times indicated that two major adsorbed U(VI) species were present in the sediment that resembled U(VI) adsorbed on quartz and phyllosilicates. Simulations of the normalized fluorescence spectra confirmed that the speciation of SPP1 GWF was best represented by a linear combination of U(VI) adsorbed on quartz (90%) and phyllosilicates (10%). However, the fluorescence quantum yield for U(VI) adsorbed on phyllosilicates was lower than quartz and, consequently, its fractional contribution to speciation may be underestimated. Spectral comparison with literature data suggested that U(VI) exist primarily as inner-sphere complexes with surface silanol groups on quartz and as surface U(VI) tricarbonate complexes on phyllosilicates. Published by Elsevier Ltd.

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Section: Reference Phasesmentioning

confidence: 99%

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confidence: 99%

Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: A fluorescence spectroscopy study

Wang

Zachara

Boily

et al. 2011

Geochimica et Cosmochimica Acta

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“…Some extractions were also conducted to characterize how much uranium desorbs from sediment after 1 h of contact time and 1000 h of contact time in order to account for the U diffusion out of microfractures, as described in Um (2010).…”

Section: 3mentioning

confidence: 99%

Remediation of Uranium in the Hanford Vadose Zone Using Ammonia Gas: FY 2010 Laboratory-Scale Experiments

Szecsody¹,

Truex²,

Zhong³

et al. 2010

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Executive SummaryThis investigation is focused on refining an in situ technology for vadose zone remediation of uranium by the addition of ammonia (NH 3 ) gas with no addition of water. The objectives were to: a) refine the technique of ammonia gas treatment, b) identify the geochemical changes in uranium surface phases, c) identify broader geochemical changes that occur, and d) predict and test injection of ammonia gas for intermediate-scale systems to identify process interactions that could impact field-scale implementation. For ammonia gas injection into vadose zone sediments to be successful as a uranium remediation technology, it needs to show decreased U mobility of the most mobile U phases (aqueous, adsorbed) in a variety of field conditions. Uranium is present in Hanford sediment include in multiple phases including aqueous U(VI)-carbonate complexes, adsorbed, uranium coprecipitated with carbonates, and U-bearing minerals Na-boltwoodite and uranophane. Ammonia treatment of sediments raises the pH in Hanford sediments from 8.0 to 11-13, which has resulted in a decrease in uranium mobility, as evidenced by decrease in aqueous and adsorbed uranium in 85% of the different sediments tested (different U surface phase distributions or NH 3 treatments) and an increase in 8M HNO 3 extracted U (hard to extract U phases, silicates/phosphates/oxides) for 79% of sediments tested. There were also inconsistent changes in two acetate extractions, likely the result of dissolution of multiple surface U phases (U-carbonates, Na-boltwoodite, uranophane). Surface phase analysis by laser induced fluorescence spectroscopy and extended x-ray absorption structure has showed essentially no U surface mineral change in sediments initially containing Na-boltwoodite, but some U surface phase changes in U-calcite coprecipitates to uranyl oxyhydroxide, Na-boltwoodite, and uranyl tricarbonate. Therefore, the ammonia gas treatment appears most effective for U present in the most mobile phases: aqueous U, adsorbed U, and carbonate associated U. NH 3 -treated sediments containing Na-boltwoodite and uranophane showed decreased leaching even though solid phase analysis showed little changes in the U mineralogy. The decreased leaching may be the result of other mineral precipitates coating these phases. Minerals that leached the most significant mass of ions were montmorillonite, muscovite, and kaolinite. A greater understanding of these dissolution/precipitation/coating processes is needed to predict the long-term impact on uranium mobility.Ammonia gas injection experiments conducted in 20-to 30-ft long 1-D systems and a layered 2-D radial flow system were used to characterize the physicochemical changes at the NH 3 reaction front and treatment coverage in heterogeneous sediments. For 5% NH 3 (95%N 2 ) injection, an average of 234 pore volumes were needed to achieve the elevated pH (10.2 to 11.4) of the reaction front observed, with 465 pore volumes needed to achieve pH equilibrium (pH = 11.88), at 4% water content and 35% porosity. The des...

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“…The important implication of this was that only 43% of the total sorbed U(VI) inventory was considered active in terms of future plume persistence and/or quantity to be remediated. Newer studies including those by Um et al (2010), Murray et al (2012), and Shang et al (In Press 1 ), indicate that recalcitrant U(VI) can become labile, as sorbed U(VI) is depleted through desorption. Labile U(VI), for example, was exhausted in Figure 5.1 after 130 pore volumes, and total contaminant U(VI) was used as the total adsorbed U(VI) concentration for modeling purposes.…”

Section: Advective Removal Of Adsorbed Uraniummentioning

confidence: 99%

“…A noteworthy, consistent database of laboratory adsorption/desorption measurements has been developed by IFRC researchers who have investigated sediments from the South Process Pond, the North Process Pond, the Process Trenches, and select intervening areas Bond et al 2008;Liu et al 2009;Um et al 2010;Shang et al 2011;Stoliker et al 2011;Murray et al 2012;Stoliker et al In Press 1 ). Chemical conditions were used for the measurements that simulate ambient 300 Area groundwater conditions (no river water component) in terms of pH, and major cations (Ca 2+ , Mg 2+ , Na + , and K + ) and anions (HCO 3 -, SO 4 2+ , and NO 3 -).…”

Section: Laboratory Measurements Of Adsorption and Desorptionmentioning

confidence: 99%

Updated Conceptual Model for the 300 Area Uranium Groundwater Plume

Zachara¹,

Freshley²,

Last³

et al. 2012

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SummaryThe 300 Area uranium groundwater plume in the 300-FF-5 Operable Unit is residual from past discharge of nuclear fuel fabrication wastes to a number of liquid (and solid) disposal sites. The source zones in the disposal sites were remediated by excavation and backfilled to grade, but sorbed uranium remains in deeper, unexcavated vadose zone sediments. Despite source term removal, the groundwater plume has shown remarkable persistence, with concentrations exceeding the drinking water standard over an area of approximately 1 km 2 . The plume resides within a coupled vadose zone, groundwater, river zone system of immense complexity and scale. Interactions between geologic structure, the hydrologic system driven by the Columbia River, groundwater-river exchange points, and the geochemistry of uranium contribute to persistence of the plume.The U.S. Department of Energy (DOE) recently completed a Remedial Investigation/Feasibility Study (RI/FS) to document characterization of the 300 Area uranium plume and plan for beginning to implement proposed remedial actions. As part of the RI/FS document, a conceptual model was developed that integrates knowledge of the hydrogeologic and geochemical properties of the 300 Area and controlling processes to yield an understanding of how the system behaves and the variables that control it. Recent results from the Hanford Integrated Field Research Challenge (IFRC) site and the Subsurface Biogeochemistry Scientific Focus Area Project funded by the DOE Office of Science were used to update the conceptual model and provide an assessment of key factors controlling plume persistence.Hanford IFRC research identified several refinements to the conceptual model that can be extended to the 300 Area. Studies at the IFRC site with geophysics, hydraulic testing, and tracers confirm the presence of a lower permeability intermediate zone within the Hanford formation that has a large impact on the hydrologic system. Resulting vertical borehole flows have implications for monitoring, persistence of the uranium plume, and remediation approach. Research at the IFRC site has shown that uranium is mobilized in a heterogeneous way from the lower vadose zone in concentrations exceeding the drinking water standard during the spring high water table event, showing large fluctuations in concentrations over the approximate 3-month period of spring snowmelt. The observed behaviors of uranium strongly impact monitoring results, and should be considered in their interpretation. Improved persistence calculations should address more accurate adsorption-desorption parameters (e.g., surface complexation) for the saturated zone derived from fitting of new IFRC field experiment data.

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Resupply mechanism to a contaminated aquifer: A laboratory study of U(VI) desorption from capillary fringe sediments

Cited by 22 publications

References 58 publications

Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: A fluorescence spectroscopy study

Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: A fluorescence spectroscopy study

Remediation of Uranium in the Hanford Vadose Zone Using Ammonia Gas: FY 2010 Laboratory-Scale Experiments

Updated Conceptual Model for the 300 Area Uranium Groundwater Plume

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