Scale-Up Information for Gas-Phase Ammonia Treatment of Uranium in the Vadose Zone at the Hanford Site Central Plateau

Truex, Michael J.; Szecsody, James E.; Zhong, Lirong; Thomle, Jonathan N.; Johnson, Timothy C.

doi:10.2172/1170499

Cited by 3 publications

(13 citation statements)

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“…Previous laboratory evaluation of gas-phase technologies focused on immobilization of uranium ) and recommended pursuing ammonia injection because it was best suited for field implementation and was effective at reducing uranium mobility. Additional study of the ammonia gas treatment process and large-scale application has also been conducted Truex et al 2014).…”

Section: Technology Descriptionmentioning

confidence: 99%

“…The long-term fate of ammonia added to the subsurface to induce uranium treatment, as described in laboratory testing (Truex et al 2014), is (1) volatilization and upward ammonia gas migration in the vadose zone, (2) microbial conversion of ammonia to nitrate in the pore water, and/or (3) ammonium sorption or incorporation into aluminosilicate precipitates. To examine the relative importance of the second and third processes, sediment dosed with 5%, 0.5%, or 0.05% ammonia gas was incubated for varying lengths of time in closed containers so that volatilization of ammonia was not possible.…”

Section: 4mentioning

confidence: 99%

“…The laboratory testing for ammonia technology development conducted prior to initiating efforts at the field test site demonstrated the treatment process and provided information needed to scale the treatment for field applications (Szecsody et al ,b, 2012Truex et al 2014). A variety of vadose zone, low-water-content sediments were treated with ammonia to evaluate the treatment.…”

Section: Overall Conclusionmentioning

confidence: 99%

“…To estimate URGS design, an equilibrium partitioning approach can be assumed for the ammonia loading into the targeted treatment area of the vadose zone. A mass balance type calculation can be used to estimate the ammonia loading needed for a targeted region of sediment at a specified water content and ammonia gas concentration (Truex et al 2014;. Additionally, ammonia dissociation can be computed based on thermodynamic information so that the pH of the pore water can also be estimated.…”

Section: Urgs Implementability Requirements and Limitationsmentioning

confidence: 99%

“…Based on these laboratory results, pH manipulation with ammonia gas was selected as the most promising reactive-gas approach to decrease the mobility of uranium. Additional laboratory efforts were applied to describe the treatment process and obtain information for scaling to field application (Szecsody et al ,b, 2012Truex et al 2014). Thus, ammonia treatment was selected for treatability testing as the URGS technology.…”

Section: Introductionmentioning

confidence: 99%

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Deep Vadose Zone Treatability Test of Uranium Reactive Gas Sequestration for the Hanford Central Plateau: Final Report

Truex

Szecsody

Strickland

et al. 2018

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Over decades of operation, the U.S. Department of Energy (DOE) and its predecessors have released nearly 2 trillion L (450 billion gal.) of liquid into the vadose zone at the Hanford Site. Much of this liquid waste discharge into the vadose zone occurred in the Central Plateau, a 200 km 2 (75 mi 2 ) area that includes approximately 800 waste sites. Some of the inorganic and radionuclide contaminants in the deep vadose zone at the Hanford Site are at depths where direct exposure pathways (human health or ecological) are not of concern, but the contamination may need to be remediated to protect groundwater. The Tri-Party Agencies (DOE, the U.S. Environmental Protection Agency, and the Washington State Department of Ecology) established Milestone M-015-50, which directed DOE to submit a treatability test plan for remediation of technetium-99 (Tc-99) and uranium in the deep vadose zone. These contaminants are mobile in the subsurface environment and have been detected at high concentrations deep in the vadose zone, and, at some locations, have reached groundwater. Testing of technologies to remediate Tc-99 and uranium will also provide information relevant to remediating other contaminants in the vadose zone. The uranium reactive gas sequestration (URGS) test described herein was conducted as an element of the deep vadose zone treatability test plan published to meet Milestone M-015-50. The URGS technology was tested as a potential remedy to decrease the mobility of uranium in the vadose zone as a mechanism to protect groundwater. Information about URGS obtained from this test is intended for use in subsequent feasibility studies for Hanford Central Plateau waste sites with uranium contamination in the deep vadose zone.

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Section: Technology Descriptionmentioning

confidence: 99%

Section: 4mentioning

confidence: 99%

Section: Overall Conclusionmentioning

confidence: 99%

Section: Urgs Implementability Requirements and Limitationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Deep Vadose Zone Treatability Test of Uranium Reactive Gas Sequestration for the Hanford Central Plateau: Final Report

Truex

Szecsody

Strickland

et al. 2018

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Gas-Phase Treatment of Technetium in the Vadose Zone at the Hanford Site Central Plateau

Truex

Szecsody

Zhong

et al. 2014

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Technetium-99 (Tc-99) is present in the vadose zone of the Hanford Central Plateau and is a concern with respect to the protection of groundwater. The persistence, limited natural attenuation mechanisms, and geochemical behavior of Tc-99 in oxic vadose zone environments must be considered in developing effective alternatives for remediation. This report describes a new in situ geochemical manipulation technique for decreasing Tc-99 mobility using a combination of geochemical Tc-99 reduction with hydrogen sulfide gas and induced sediment mineral dissolution with ammonia vapor, which create conditions for deposition of stable precipitates that decrease the mobility of Tc-99. Laboratory experiments were conducted to examine changes in Tc-99 mobility in vadose zone sediment samples to evaluate the effectiveness of the treatment under a variety of operational and sediment conditions. The laboratory experiments demonstrated a robust treatment approach to decrease the mobility of Tc-99 in the vadose zone at the Hanford Central Plateau using gas-phase amendments. The gas-phase Tc-99 treatment was shown to be effective for a variety of operational and site conditions, including 1) sequential and parallel addition of hydrogen sulfide and ammonia gases over a range of treatment gas concentrations, 2) Tc-99 concentrations ranging from 34 to 3800 pCi/g, 3) soil moisture contents of 1, 4, and 8 wt%, and 4) gas delivery times into the sample ranging from minutes to hours. A large fraction of Tc-99 in treated sediments was also shown be resistant to leaching in saturated soil column tests. These laboratory results suggest that the combined hydrogen sulfide and ammonia gas treatment is a viable candidate for treatment to decrease the mobility of Tc-99 in the vadose zone. The combined-gas Tc-99 treatment technique is an extension of the ammonia gas treatment for uranium. Previous efforts have examined many aspects of the ammonia treatment process, including key information needed to scale this process to field application. Much of this scale-up information is applicable to field application of the combined hydrogen sulfide and ammonia gas treatment demonstrated in this study to decrease Tc-99 mobility. The information presented herein suggests that, with moderate additional scale-up investigation, the combined-gas Tc-99 treatment could be field tested. Key scale-up elements would include evaluating the fate and transport of hydrogen sulfide gas in the subsurface in the presence of ammonia gas to support determining safe operational conditions for use of hydrogen sulfide. Some additional information on the reaction rates and processes in relation to subsurface pH conditions and Tc-99 precipitate stability and whether microbial processes interact with these reactions will also be important. For health and safety reasons, it may be important to minimize field collection of gas samples for treatment monitoring. Thus, extension of the electrical resistivity tomography monitoring previously applied for soil desiccation and researched fo...

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Evaluation of Central Plateau Remediation Alternatives: Interim Status Report

Bagwell

Lawter

Cantrell

et al. 2018

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Scale-Up Information for Gas-Phase Ammonia Treatment of Uranium in the Vadose Zone at the Hanford Site Central Plateau

Cited by 3 publications

References 13 publications

Deep Vadose Zone Treatability Test of Uranium Reactive Gas Sequestration for the Hanford Central Plateau: Final Report

Deep Vadose Zone Treatability Test of Uranium Reactive Gas Sequestration for the Hanford Central Plateau: Final Report

Gas-Phase Treatment of Technetium in the Vadose Zone at the Hanford Site Central Plateau

Evaluation of Central Plateau Remediation Alternatives: Interim Status Report

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