Iron oxide waste form for stabilizing 99Tc

Um, Wooyong; Chang, Hyun-Shik; Icenhower, Jonathan P.; Lukens, Wayne W.; Serne, R. Jeffrey; Qafoku, Nikolla P.; Kukkadapu, Ravi; Westsik, Joseph H.

doi:10.1016/j.jnucmat.2012.06.004

Cited by 45 publications

(56 citation statements)

References 32 publications

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“…The environmental concern with 99 Tc is its high mobility in subsurface soils and long half-life (2.1 × 10 5 year). The highly soluble TcO 4 − does not adsorb well onto the surface of minerals [8][9][10] and, thus, migrates nearly at the same velocity as groundwater [11]. More importantly, the primary concern with processing the 99 Tc-containing waste into a glass is its extreme volatility, which results in low concentrations of Tc retained in the final product relative to target concentrations [12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Jin

Kim

Tucker

et al. 2015

Journal of Non-Crystalline Solids

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a b s t r a c tVolatile loss of radioactive technetium-99 ( 99 Tc) to off-gas is a major challenge when vitrifying low-activity waste (LAW) at the U.S. Department of Energy's Hanford Site in Washington State. We investigated the partitioning and incorporation of rhenium (Re) (a nonradioactive surrogate for 99 Tc) into the glass melt during crucible melting of two simulated LAW feeds that have exhibited a large difference in 99m Tc/Re retention in glass from small-scale melter tests. Each feed was prepared from a simulated liquid LAW and additives (boric acid, silica sand, etc.). The as-mixed slurry feeds were dried at 105°C and heated to 600-1100°C at 5 K/min. The dried feeds and heat-treated samples were leached with deionized water for 10 min at room temperature followed by 24-h leaching at 80°C. Chemical compositions of the resulting solutions and insoluble solids were analyzed. Volume expansion measurements and X-ray diffraction (XRD) analyses were performed on dried feeds and heat-treated samples to characterize the progress of feed-to-glass conversion reactions. We found that incorporation of Re into the glass melt was virtually completed during the major feed-to-glass conversion reactions that occurred at ≤700°C. The results of our study suggest that the different compositions of the salt phases formed during early stages of melting at ≤700°C are responsible for the large difference in Re incorporation into the glass melt in these two feeds.

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Section: Introductionmentioning

confidence: 99%

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Jin

Kim

Tucker

et al. 2015

Journal of Non-Crystalline Solids

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“…The measured reductive capacities of the 99 Tc-goethite 2-5 and 2-2 samples before leaching were 0.140 meq/g and 0.744 meq/g, respectively. Although low reductive capacity was measured in the 99 Tc-goethite 2-5 sample, which was prepared with additional armoring, than in the 2-2 sample, which was prepared without additional armoring (Um et al 2011), more leachable 99 Tc concentrations were found in 99 Tc-goethite 2-2 sample than in the 2-5 sample under the same leaching solution conditions (Um et al 2012). Therefore, the limited 99 Tc reoxidation found in the 99 Tc-goethite 2-5 sample may result from a physical barrier effect rather than chemical reductive capacity preserved in the magnetite mineral that was present more in the final 99 Tc-goethite 2-2 sample.…”

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confidence: 83%

“…Removal of 99 Tc is also possible through a coprecipitation process with respect to maghemite or magnetite as reduced Tc(IV) species. Remaining Tc mass in solution (%) Geckeis et al (2012) found that 99 Tc(IV) tends to be fully compatible with the hematite lattice, and Um et al (2012) …”

Section: Intensity (Counts)mentioning

confidence: 99%

“…While many of the proposed disposal options rely on isolating 99 Tc(IV) from oxidizing components in gas or aqueous fluid, the reductive capacity of the material hosting 99 Tc(IV) and the mechanism preventing the reoxidation of 99 Tc(IV) Tc(IV), which then coprecipitates with the goethite-dominant iron (oxy)hydroxide mineral phase (Um et al 2010). The final product also exhibits very slow weathering and low 99 Tc leachability rates in subsurface environment conditions (Um et al 2011(Um et al , 2012. Despite the positive results for 99 Tc removal and long-term sequestration in a solidifying goethite waste form, more fundamental understanding of the processes that control the 99 Tc(VII) reduction and the location of 99 Tc(IV) in the final Fe (oxy)hydroxide mineral lattice is needed.…”

mentioning

confidence: 99%

“…Because the powdered 99 Tc-goethite sample 2-5 was prepared with additional goethite armoring (Um et al 2011) and showed the highest 99 Tc(IV) contribution (~100%) as prepared (Um et al 2012), Tc-goethite sample 2-5 is considered to the most resistant to 99 Tc reoxidation and leaching, even after less than three years in the oxidizing condition. Remaining Tc mass in solution (%) at 42/14 days 99 Tc-goethite 2-5 samples as prepared and after 6-month leaching in the IDF pore water solution were obtained from Um et al (2011Um et al ( , 2012, and are shown together with new XANES results for the 99 Tc-goethite 2-5 samples reacted for three years (see Table 2 for XAFS sample information). The oxidation state of 99 Tc in the reacted 99 Tc-goethite 2-5 samples after either leaching in the IDF solution or in air was determined by fitting their XANES spectra using a linear combination model with the spectra for the 99 TcO 4 -and the 99 TcO 2 •2H 2 O standards.…”

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Technetium Removal Using Tc-Goethite Coprecipitation

Um¹,

Wang²,

Jung³

et al. 2013

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Executive SummaryThis report describes the results from laboratory tests performed at Pacific Northwest National Laboratory for the U.S. Department of Energy (DOE) EM-31 Support Program (EMSP) subtask, "Low temperature waste forms coupled with technetium removal using an alternative immobilization process such as Fe(II) treated-goethite precipitation" to increase our understanding of 99 Tc long-term stability in goethite mineral form and the process that controls the 99 Tc(VII) reduction and removal by the final Fe (oxy)hydroxide mineral forms.The overall objectives of this task were to 1) evaluate the transformation process of Fe (oxy)hydroxide minerals to more crystalline goethite (α-FeOOH) Tc removal was not considered to be from surface adsorption, but incorporation into transformed mineral product. Although a further analysis is essential to confirm 99 Tc speciation in the final transformed product from Fe(OH) 2 (s), mineral transformation from Fe(OH) 2 (s) can be used to effectively remove 99 Tc(VII) in alkaline pH conditions germane to off-gas scrubber secondary waste and low-activity waste streams. Slightly more transformation products were also found from Fe(OH) 2 (s) with a solution-to-solid ratio of 100 than with a ratio of 1000. The transformation product from ferrihydrite was similar, and solely goethite mineral was produced in most of the conditions. It is clear that comparison results from both Fe(OH) 2 (s) and ferrihydrite substrates show that high slurry pH and high temperature conditions favor more goethite formation from the transformation reaction. Unfortunately, we could not conduct 99 Tc removal using ferrihydrite as an initial substrate in this task, but based on previous results (Um et al. 2010), ferrihydrite can also be used to remove 99 Tc with additional aqueous Fe(II). Transformation product from magnetite was very limited and there were only small amounts of maghemite and goethite formed from magnetite reacted as initial substrate under high pH and temperature conditions. In addition, negligible 99 Tc removal (<5%) from solution was also found in magnetite slurry without aqueous Fe(II) addition.Even after long-term leaching in the Integrated Disposal Facility (IDF) pore water solution for two years, very limited amounts of 99 Tc and Fe(total) were detected in the IDF leachates. The limited 99 Tc release was attributed to more stabilized 99 Tc(IV) present in 99 Tc-goethite lattice even after long-term exposure to oxygen, while zero detected Fe(total) concentration in the IDF leachate indicated that the iv structure of the final goethite mineral was stable in a circumneutral pH condition similar to the IDF pore water. Reduced 99 Tc(IV) incorporated in the goethite was unlikely to be reoxidized to 99 Tc(VII), even when the final 99 Tc-goethite product (sample 2-5) was exposed to oxidizing conditions for three years (two years in IDF solution plus one year in air). In addition, the measured reductive capacity of both 99 Tc-goethite 2-2 sample (prepared without additional armoring pro...

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Synthesis and Characterization of Non‐Aqueous [Tc^XM‐PW₁₁O₃₉]ⁿ^– with M = O, N: Comparing Tc^V and Tc^VI in Metal Oxide Matrices

et al. 2019

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Technetium-99, a prevalent by-product of the nuclear fuel cycle, is a transition metal with 9 accessible oxidation states and a half-life of 2.1 × 10 5 years. 99 Tc VII has been found in the environment surrounding National Lab sites and fuel reprocessing centers, and its separation and long-term storage is complicated by its extensive redox chemistry. In our prior work we have reported the synthesis and reduction of Tc V O to Tc IV O in α 1 -and α 2 -Wells-Dawson P 2 W 17 O 61 10polyoxometalates and reported on the polyoxometalate features that promote reduc- [a]

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Iron oxide waste form for stabilizing 99Tc

Cited by 45 publications

References 32 publications

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Technetium Removal Using Tc-Goethite Coprecipitation

Synthesis and Characterization of Non‐Aqueous [Tc^XM‐PW₁₁O₃₉]ⁿ^– with M = O, N: Comparing Tc^V and Tc^VI in Metal Oxide Matrices

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Iron oxide waste form for stabilizing 99Tc

Cited by 45 publications

References 32 publications

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Reactions during melting of low-activity waste glasses and their effects on the retention of rhenium as a surrogate for technetium-99

Technetium Removal Using Tc-Goethite Coprecipitation

Synthesis and Characterization of Non‐Aqueous [TcXM‐PW11O39]n– with M = O, N: Comparing TcV and TcVI in Metal Oxide Matrices

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Synthesis and Characterization of Non‐Aqueous [Tc^XM‐PW₁₁O₃₉]ⁿ^– with M = O, N: Comparing Tc^V and Tc^VI in Metal Oxide Matrices