Letter Report: LAW Simulant Development for Cast Stone Screening Test

Russell, Renee L.; Westsik, Joseph H.; Swanberg, David J.; Eibling, R.E.; Cozzi, A. D.; Lindberg, Michael J.; Josephson, Gary B.; Rinehart, Donald E.

doi:10.2172/1096128

Cited by 25 publications

(34 citation statements)

References 6 publications

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“…4 Cr(VI) has a more favorable reduction potential, -0.16 V vs -0.36 V for Tc(VII) at pH 14, [15][16] and exists in Hanford nuclear waste streams at concentrations orders of magnitude greater than Tc. 17 As a result, reductants added to reduce Tc(VII) are consumed by Cr(VI). Thus, there remains a critical need for treatment technologies that can reduce Tc(VII) in the presence of Cr(VI).…”

Section: Introductionmentioning

confidence: 99%

“…19 As such, the exact LAW composition for treatment is not known, so for the purpose of this work, an overall average LAW simulant composition is used based on output from the Hanford Tank Waste Operations Simulator (HTWOS) model. 17 To arrive at this average composition, which includes nitrate, nitrite, sulfate, aluminum, Cr(VI) and other minor constituents, the HTWOS model tracks tank waste storage, retrieval, and multiple treatment and immobilization processes over ~20 years of operation.…”

Section: Introductionmentioning

confidence: 99%

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Cr(VI) Effect on Tc-99 Removal from Hanford Low-Activity Waste Simulant by Ferrous Hydroxide

Saslow

Pearce

et al. 2018

Environ. Sci. Technol.

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Here, Cr(VI) effects on Tc-immobilization by Fe(OH)(s) are investigated while assessing Fe(OH)(s) as a potential treatment method for Hanford low-activity waste destined for vitrification. Batch studies using simulated low-activity waste indicate that Tc(VII) and Cr(VI) removal is contingent on reduction to Tc(IV) and Cr(III). Furthermore, complete removal of both Cr and Tc depends on the amount of Fe(OH)(s) present, where complete Cr and Tc removal requires more Fe(OH)(s) (∼200 g/L of simulant), than removing Cr alone (∼50 g/L of simulant). XRD analysis suggests that Fe(OH)(s) reaction and transformation in the simulant produces mostly goethite (α-FeOOH), where Fe(OH)(s) transformation to goethite rather than magnetite is likely due to the simulant chemistry, which includes high levels of nitrite and other constituents. Once reduced, a fraction of Cr(III) and Tc(IV) substitute for octahedral Fe(III) within the goethite crystal lattice as supported by XPS, XANES, and/or EXAFS results. The remaining Cr(III) forms oxide and/or hydroxide phases, whereas Tc(IV) not fully incorporated into goethite persists as either adsorbed or partially incorporated Tc(IV)-oxide species. As such, to fully incorporate Tc(IV) into the goethite crystal structure, additional Fe(OH)(s) (>200 g/L of simulant) may be required.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Cr(VI) Effect on Tc-99 Removal from Hanford Low-Activity Waste Simulant by Ferrous Hydroxide

Saslow

Pearce

et al. 2018

Environ. Sci. Technol.

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“…3,4,5 • Determine the relationship between the Cast Stone reduction capacity measured by the Angus-Glasser Method 6 and leachability of Tc from depth discrete samples.…”

Section: Objectivesmentioning

confidence: 99%

Cast Stone Oxidation Front Evaluation: Preliminary Results For Samples Exposed To Moist Air

Langton¹,

Almond²

2013

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“…A detailed description of the LAW simulant development work is provided in Russell et al (2013). Saltcake is a predominant form of wastes in a large fraction of the single-shell tanks (SSTs) at the Hanford Site.…”

Section: Waste Simulantsmentioning

confidence: 99%

Characterization of Technetium Speciation in Cast Stone

Um¹,

Jung²,

Wang³

et al. 2013

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Executive SummaryThis report describes the results from laboratory tests performed at Pacific Northwest National Laboratory (PNNL) for the U.S. Department of Energy (DOE) EM-31 Support Program (EMSP) subtask, "Production and Long-Term Performance of Low Temperature Waste Forms" to provide additional information on technetium (Tc) speciation characterization in the Cast Stone waste form. To support the use of Cast Stone as an alternative to vitrification for solidifying low-activity waste (LAW) and as the current baseline waste form for secondary waste streams at the Hanford Site, additional understanding of Tc speciation in Cast Stone is needed to predict the long-term Tc leachability from Cast Stone and to meet the regulatory disposal-facility performance requirements for the Integrated Disposal Facility (IDF). Characterizations of the Tc speciation within the Cast Stone after leaching under various conditions provide insights into how the Tc is retained and released. The data generated by the laboratory tests described in this report provide both empirical and more scientific information to increase our understanding of Tc speciation in Cast Stone and its release mechanism under relevant leaching processes for the purpose of filling data gaps and to support the long-term risk and performance assessments of Cast Stone in the IDF at the Hanford Site.Various formulations of Cast Stone that include secondary waste simulants and different LAW simulants have been characterized previously. For this report, smaller Cast Stone monoliths were prepared with high Tc concentrations spiked into the 7.8 M Na overall average LAW simulant using dry ingredients from two different sources (referred to as NW and SE). These small Cast Stone monoliths were used for this Tc speciation characterization. The following subtasks are included within the Tc speciation characterization task:1. Measure the reductive capacity of different types of dry ingredients, the 8 LAW simulants used in Westsik et al. (2013), and short-term cured Cast Stone before and after leaching with different leaching conditions. The reductive capacities of dry ingredients from NW and SE sources, various LAW simulants, and final Cast Stone before and after leaching tests were measured using two different methods, the Ce(IV) and Cr(VI) methods. One type of blast furnace slag (BFS) and the high-Ca fly ash were obtained from LaFarge North America Inc. in Pasco, Washington, and these materials are referred to as the NW slag and fly ash. The second BFS and the low-Ca fly ash are the same materials used in the Saltstone processing facility at the Savannah River Site in South Carolina and are referred to as the SE materials. Much more of the solids dissolve in the strong acid (pH ~1-2) environment created by the Ce(IV) method compared to circumneutral pH (~7.0) condition created by the Cr(VII) method. Among the dry ingredients, the reductive capacity measured by the Ce(IV) method was the highest for BFS (0.793 meq/g for NW slag and 0.800 meq/g for SE slag). The reductive ...

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Letter Report: LAW Simulant Development for Cast Stone Screening Test

Cited by 25 publications

References 6 publications

Cr(VI) Effect on Tc-99 Removal from Hanford Low-Activity Waste Simulant by Ferrous Hydroxide

Cr(VI) Effect on Tc-99 Removal from Hanford Low-Activity Waste Simulant by Ferrous Hydroxide

Cast Stone Oxidation Front Evaluation: Preliminary Results For Samples Exposed To Moist Air

Characterization of Technetium Speciation in Cast Stone

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