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

Szecsody, James E.; Truex, Michael J.; Zhong, Lirong; Qafoku, Nikolla P.; Williams, Mark; McKinley, James P.; Wang, Zheming; Bargar, John R.; Faurie, Danielle K.; Resch, Charles T.; Phillips, J. E.

doi:10.2172/1006311

Cited by 11 publications

(39 citation statements)

References 38 publications

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“…Aqueous U(VI) from extractions was measured by laser-induced kinetic phosphorimetry (KPA, Brina and Miller 1992). Phosphate precipitates were measured on sediments in experiments using a 0.5-mol/L HNO 3 × 15-minute extraction (Szecsody et al 2010). …”

Section: Solid and Aqueous Solution Analysismentioning

confidence: 99%

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

Szecsody¹,

Zhong²,

Oostrom³

et al. 2012

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SummaryThe primary objective of this study is to summarize the laboratory investigations performed to evaluate short-and long-term effects of phosphate treatment on uranium leaching from 300 Area smear zone sediments. Column studies were used to compare uranium leaching in phosphate-treated to untreated sediments over a year with multiple stop flow events to evaluate longevity of the uranium leaching rate and mass. Phosphate treatment may decrease leaching by non-uranium calcium-phosphate precipitates coating uranium surface phases, uranium adsorption to precipitates, or slow formation of uranium-phosphate precipitates. A secondary objective was to compare polyphosphate injection, polyphosphate/xanthan injection, and polyphosphate infiltration technologies that deliver phosphate to sediment.Although phosphate treatment did not completely eliminate uranium leaching from sediment, the long-term decrease in leaching rate, leached mass, and changes in nonlabile uranium were significant compared with untreated sediment. Under idealized laboratory conditions, a wide range of phosphate treatments resulted in a significant (average 54%) long-term (to 1 year) decrease in leached uranium mass.A comparison of a high phosphate treatment to no treatment over a time period of 4500 h shows the evolution of phosphate-treated sediment from initial high efficiency to remove uranium from solution to decreased efficiency over a long period of time. The injection strategy for polyphosphate treatment of sediments that resulted in the greatest decrease in uranium leaching was to: a) maximize the no-flow phosphate-sediment reaction time before groundwater advection, b) use a high (~50 mM) phosphate concentration, and c) use xanthan with the polyphosphate solution. Some limitations of polyphosphate treatment technologies were identified, which impact field-scale applicability in different treatment zones. Because the rate at which uranium is removed from solution in the presence of phosphate precipitates is slow, the phosphate treatment will be most effective in low flow zones (i.e., smear zone where groundwater flow occurs only seasonally). Although xanthan addition (to increase solution viscosity and improve access to low-K zones) to polyphosphate showed the greatest consistent decrease in leached uranium, viscosity decreases rapidly (half-life 52 h). Because the high viscosity of the solution needs to be maintained for weeks in order to have sufficient phosphate-sediment contact in a potential smear zone application, additional research is needed. The mass of phosphate precipitate needed to decrease uranium leaching is significant, although polyphosphate and polyphosphate/xanthan injections precipitated sufficient mass (0.18 to 0.28 mg PO 4 /g). While polyphosphate solution infiltration resulted in significantly greater precipitate mass, further optimization of an infiltration strategy is needed to precipitate sufficient phosphate at 20-25 ft depth needed for field scale use. Given field-scale spatial/ temporal variation in uranium c...

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Section: Solid and Aqueous Solution Analysismentioning

confidence: 99%

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

Szecsody¹,

Zhong²,

Oostrom³

et al. 2012

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“…Recently, Szecsody et al (2010aSzecsody et al ( , 2010b applied the series of six sequential sediment extractions listed below as an operational means to quantify how uranium is distributed within a sediment sample. These extractions progress through increasingly harsh reagents.…”

Section: Uranium Contamination Backgroundmentioning

confidence: 99%

“…These data suggest that some of the uranium in contaminated Hanford Site sediments is currently resistant to extraction by mild extraction solutions. The extraction solutions from Szecsody et al (2010aSzecsody et al ( , 2010b include the following elements:…”

Section: Uranium Contamination Backgroundmentioning

confidence: 99%

“…One potentially significant difference is the oxidation state of uranium in the targeted solid phase. The solid phase and adsorbed uranium in the 200 Area contaminated soil is predominantly in the oxidized form uranium(VI) (Szecsody et al 2010a(Szecsody et al , 2010b, whereas uranium in natural deposits that are mined using ISR is typically present as uranium(IV), which is the reduced form. In addition, most ISR-targeted uranium deposits are located below the water table, in contrast to the vadose zone location of the uranium contamination in the 200 Area soils.…”

Section: Uranium Leaching Backgroundmentioning

confidence: 99%

“…Many of the leaching processes are mild extraction solutions that are primarily designed to address uranium that is already in relatively mobile forms. As shown in Szecsody et al (2010aSzecsody et al ( , 2010b, much of the uranium in the Hanford Site vadose zone is present in forms that require a harsh extraction solution to render them mobile. Thus, use of mild extraction solutions would need to be evaluated in terms of whether these solutions can remove a sufficient fraction of the total uranium to meet remediation goals.…”

Section: Soil Flushing Was Included In the Deep Vadose Zone Treatabilmentioning

confidence: 99%

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Evaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau

Truex¹,

Oostrom²,

Zhang³

et al. 2010

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Soil flushing was included in the Deep Vadose Zone Treatability Test Plan for the Hanford CentralPlateau (DOE-RL 2008 1 ) as a technology with the potential to remove contaminants from the vadose zone. Soil flushing operates through the addition of water, and if necessary an appropriate mobilizing agent, to mobilize contaminants and flush them from the vadose zone and into the groundwater where they are subsequently captured by a pump-and-treat system. There are uncertainties associated with applying soil flushing technology to contaminants in the deep vadose zone at the Hanford Central Plateau. The modeling and laboratory efforts reported herein are intended to provide a quantitative assessment of factors that impact water infiltration and contaminant flushing through the vadose zone and into the underlying groundwater. Once in the groundwater, capture of the contaminants would be necessary, but this aspect of implementing soil flushing was not evaluated in this effort. Soil flushing was evaluated primarily with respect to applications for technetium and uranium contaminants in the deep vadose zone of the Hanford Central Plateau. SummarySoil flushing operates through addition of water, and if necessary an appropriate mobilizing agent, to mobilize contaminants and flush them from the vadose zone and into the groundwater where they are subsequently captured by a pump-and-treat system. As described in the Deep Vadose Zone Treatability Test Plan for the Hanford Central Plateau (DOE-RL 2008), investigation of these vadose zone processes through modeling and laboratory evaluation is needed as a first step in providing information for considering soil flushing in subsequent feasibility studies for the Hanford Site deep vadose zone.Numerical modeling and laboratory flow-cell experiments were conducted to investigate the characteristics of water flow and solute transport through the vadose zone as a function of the imposed infiltration condition, subsurface properties, and properties of the leaching solution. Information on previous uranium leaching studies, infiltration studies at the Hanford Site data, and relevant uranium mining operations were compiled and evaluated with respect to how these approaches potentially apply to soil flushing in the Hanford Central Plateau.There are uncertainties associated with applying soil flushing technology to contaminants in the deep vadose zone at the Hanford Central Plateau. Modeling and laboratory efforts reported herein are intended to provide a quantitative assessment of factors that impact water infiltration and contaminant flushing through the vadose zone and into the underlying groundwater. Once in the groundwater, capture of the contaminants would be necessary, but this aspect of implementing soil flushing was not evaluated in this effort. Soil flushing was evaluated primarily with respect to applications for technetium and uranium contaminants in the deep vadose zone of the Hanford Central Plateau.Contaminants such as technetium do not interact significantly...

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The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

Katsenovich

Cardona

Lapierre

et al. 2016

Applied Geochemistry

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Remediation of uranium in the deep unsaturated zone is a challenging task, especially in the presence of oxygenated, high-carbonate alkalinity soil and pore water composition typical for arid and semi-arid environments of the western regions of the U.S. This study evaluates the effect of various pore water constituencies on changes of uranium concentrations in alkaline conditions, created in the presence of reactive gases such as NH 3 to effectively mitigate uranium contamination in the vadose zone sediments. This contaminant is a potential source for groundwater pollution through slow infiltration of soluble and highly mobile uranium species towards the water table. The objective of this research was to evaluate uranium sequestration efficiencies in the alkaline synthetic pore water solutions prepared in a broad range of Si, Al, and bicarbonate concentrations typically present in field systems of the western U.S. regions and identify solid uranium-bearing phases that result from ammonia gas treatment. In previous studies (Szecsody et al. 2012, Zhong et al. 2015), although uranium mobility was greatly decreased, solid phases could not be identified at the low uranium concentrations in fieldcontaminated sediments. The chemical composition of the synthetic pore water used in the experiments varied for silica (5 to 250 mM), Al 3+ (2.8 or 5 mM), HCO 3 ‾ (0-100 mM) and U(VI) (0.0021-0.0084 mM) in the solution mixture. Experiment results suggested that solutions with Si concentrations higher than 50 mM exhibited greater removal efficiencies of U(VI). Solutions with higher concentrations of bicarbonate also exhibited greater removal efficiencies for Si, Al, and U(VI). Overall, the silica polymerization reaction leading to the formation of Si gel correlated with the removal of U(VI), Si, and Al from the solution. If no Si polymerization was observed, there was no U removal from the supernatant solution. Speciation modeling indicated that the dominant uranium species in the presence of bicarbonate were anionic uranyl 3 carbonate complexes (UO 2 (CO 3) 2-2 and UO 2 (CO 3) 3-4) and in the absence of bicarbonate in the solution, U(VI) major species appeared as uranyl-hydroxide (UO 2 (OH) 3 ‾ and UO 2 (OH) 4-2) species. The model also predicted the formation of uranium solid phases. Uranyl carbonates as rutherfordine [UO 2 CO 3 ], cejkaite [Na 4 (UO2)(CO 3) 3 ] and hydrated uranyl silicate phases as Naboltwoodite [Na(UO 2)(SiO 4). 1.5H 2 O] were anticipated for most of the synthetic pore water compositions amended from medium (2.9mM) to high (100mM) bicarbonate concentrations.

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

Cited by 11 publications

References 38 publications

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

Evaluation of Soil Flushing for Application to the Deep Vadose Zone in the Hanford Central Plateau

The effect of Si and Al concentrations on the removal of U(VI) in the alkaline conditions created by NH3 gas

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