Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation

Um, Wooyong; Chang, Hyun-Shik; Icenhower, Jonathan P.; Lukens, Wayne W.; Serne, R. Jeffrey; Qafoku, Nikolla P.; Westsik, Joseph H.; Buck, Edgar C.; Smith, Steven C.

doi:10.1021/es104343p

Cited by 127 publications

(132 citation statements)

References 33 publications

(66 reference statements)

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“…Bottom XANES spectrum corresponding to a TcO 4 − reference sample. The reader is referred to previous publications for the XANES spectra of a TcO 2 (s) reference [20,50,51].…”

Section: Corroding Fe Powder Systemsmentioning

confidence: 99%

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Yalçıntaş

Gaona²,

Scheinost

et al. 2014

Radiochimica Acta

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Redox speciation of Tc in the aqueous phase was further confirmed by solvent extraction. A good agreement is obtained between the experimentally determined Tc redox distribution and thermodynamic calculations based on NEA-TDB (Nuclear Energy Agency, Thermochemical Database) and ionic strength corrections by SIT or Pitzer approaches. These observations indicate that experimental pH c and h values in buffered systems can be considered as reliable parameters to predict the redox behaviour of Tc in dilute to highly concentrated NaCl and MgCl 2 solutions. h of the system and aqueous concentration of Tc(IV) in equilibrium with TcO 2 ⋅ 1.6H 2 O(s) are strongly affected by elevated ionic strength, especially in the case of 4.5 M MgCl 2 solutions. In such concentrated brines and under alkaline conditions (pH c = pH max ∼ 9), kinetics play a relevant role and thermodynamic equilibrium for the system Tc(IV)(aq) ⇔ Tc(IV)(s) was not attained from oversaturation conditions within the timeframe of this study (395 days). Tc(VII) is reduced to Tc(IV) by magnetite, mackinawite and siderite suspensions at pH c = 8-9 in concentrated NaCl and MgCl 2 solutions. Sorption is very high in

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“…Bottom XANES spectrum corresponding to a TcO 4 − reference sample. The reader is referred to previous publications for the XANES spectra of a TcO 2 (s) reference [20,50,51].…”

Section: Corroding Fe Powder Systemsmentioning

confidence: 99%

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Yalçıntaş

Gaona²,

Scheinost

et al. 2014

Radiochimica Acta

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“…A previously well-developed method was used to prepare 99 Tc-goethite samples designated 2-2 (prepared without additional armoring process) and 2-5 (with additional Fe(III) armoring) according to the method in Um et al (2010Um et al ( , 2011. Between 2.75 and 3.5 g of synthesized goethite powder were resuspended in 250 mL of DI water in the anaerobic chamber to minimize the oxidation of the ferrous solution prior to its use.…”

Section: Tc-goethite 2-2 and 2-5 Samplesmentioning

confidence: 99%

“…The 99 Tc-goethite powder samples, sample 2-2 that was prepared without an additional armoring process and sample 2-5 that was prepared with an armoring process (Um et al 2011) were ground to a homogeneous powder and used to determine reductive capacity. In the Ce(IV) method, a Ce(IV) stock solution [(NH 4 ) 4 Ce(SO 4 ) 4 •2H 2 O] was prepared in 10% H 2 SO 4 with a concentration of 30-60 mM depending on the reductive capacity of the specimen.…”

Section: Reductive Capacity Measurementmentioning

confidence: 99%

“…Through a coprecipitation process with respect to goethite, this mineral has proven effective in capturing and sequestering 99 Tc from simulated off-gas scrubber solutions (Um et al 2010 Tc(IV) tends to have a full compatibility with the goethite and hematite lattice (Um et al 2011;Geckeis et al 2012) and quantum chemistry calculations predict energetically more favorable incorporation of 99 Tc(IV) in the hematite lattice than 99 Tc(VII) (Skomurski et al 2010). However, upon contact with O 2 , reduced 99 Tc(IV) species generally reoxidizes rapidly, and reoxidation leads to formation of the soluble 99 Tc(VII) oxyanion (Lukens et al 2005) in cementitious waste form.…”

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.…”

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confidence: 99%

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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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Fast Room‐Temperature Synthesis of an Extremely Alkaline‐Resistant Cationic Metal–Organic Framework for Sequestering TcO₄⁻ with Exceptional Selectivity

Kang

Liu

Zhang

et al. 2022

Adv Funct Materials

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Leveraging metal–organic framework (MOF) to eliminate radioactive contaminants has invariably received much attention, but low preparation efficiency and poor selectivity have still limited its actual application. Herein, it is found that a fourfold interpenetrated cationic MOF (Ag‐TPPE) can be rapidly synthesized by only mixing, stirring, or sonication at room temperature. More impressively, the preparation process can be completed in <1 min. Up to now, this is the first report that cationic MOFs can be obtained by directly mixing the corresponding raw materials at room temperature. In addition to holding the rare merits of structural stability in extremely strong bases (8 m NaOH), Ag‐TPPE can selectively remove TcO4− in the presence of large excess SO42− or NO3−. Based on its ultra‐high selectivity, Ag‐TPPE exhibits exceptional removal rate for TcO4− from simulated Hanford and Savannah River Site waste streams, which refreshes the record of selective sorption of TcO4− at low solid/liquid ratio, overcoming the drawback of overused sorbent in treatment of radioactive waste solution. Such superior sorption capabilities are thoroughly elucidated by the density functional theory calculations on a molecular level, clearly disclosing that TcO4− can enter into the framework through breathing effect and is trapped in the large cavity through dense hydrogen bonds.

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Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation

Cited by 127 publications

References 33 publications

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Technetium Removal Using Tc-Goethite Coprecipitation

Fast Room‐Temperature Synthesis of an Extremely Alkaline‐Resistant Cationic Metal–Organic Framework for Sequestering TcO₄⁻ with Exceptional Selectivity

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Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation

Cited by 127 publications

References 33 publications

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl2 solutions

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl2 solutions

Technetium Removal Using Tc-Goethite Coprecipitation

Fast Room‐Temperature Synthesis of an Extremely Alkaline‐Resistant Cationic Metal–Organic Framework for Sequestering TcO4− with Exceptional Selectivity

Contact Info

Product

Resources

About

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Redox chemistry of Tc(VII)/Tc(IV) in dilute to concentrated NaCl and MgCl₂ solutions

Fast Room‐Temperature Synthesis of an Extremely Alkaline‐Resistant Cationic Metal–Organic Framework for Sequestering TcO₄⁻ with Exceptional Selectivity