Characterizing technetium in subsurface sediments for contaminant

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Characterizing technetium in subsurface sediments for contaminant remediation Carolyn I. Pearce, R. Jeffrey Serne, Sarah A. Saslow, Wooyong Um, R. Matthew Asmussen, Micah D. Miller, Odeta Qafoku, Michelle M.V. Snyder, Charles Tom Resch, Kayla C. Johnson, Guohui Wang, Steve M. Heald, Jim Szecsody, John Zachara, Nikolla P. Qafoku, Andrew E. Plymale, and Vicky L. Freedman ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.8b00077 • Publication Date (Web): 05 Sep 2018 Downloaded from http://pubs.acs.org on September 8, 2018

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ACS Earth and Space Chemistry

Characterizing technetium in subsurface sediments for contaminant remediation Carolyn I. Pearce*, †; R. Jeffrey Serne†; Sarah A. Saslow†; Wooyong Um‡; Robert M. Asmussen†; Micah D. Miller†; Odeta Qafoku†; Michelle M.V. Snyder†; Charles T. Resch†; Kayla C. Johnson†; Guohui Wang†; Steve M. Heald§; Jim E. Szecsody†; John M. Zachara†; Nikolla P. Qafoku†; Andrew. E. Plymale†; Vicky L. Freedman† †

Pacific Northwest National Laboratory, Richland, WA

‡

Pohang University of Science and Technology (POSTECH), Pohang, South Korea

§

Advanced Photon Source, Argonne, IL

Corresponding Author: *

[email protected]

KEYWORDS: Technetium, subsurface contamination, Solid phase characterization, X-ray absorption spectroscopy; Autoradiography

ABSTRACT: Technetium-99 (Tc) contamination remains a major environmental problem at legacy nuclear reprocessing sites, including the Hanford Site (Washington State, USA) where ~700 Ci of Tc has been released into the subsurface. Developing enhanced attenuation and

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ACS Earth and Space Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

efficient remediation strategies for released Tc requires a complete understanding of retardation processes and Tc mass flux, including the different mechanisms by which Tc is immobilized in the subsurface and the effect of localized subsurface conditions. Selection of over 30 sediments from Hanford waste disposal sites, based on historical information and sediment characterization, for analysis by autoradiography revealed that Tc concentrations were generally below the detection limit of 5 mg Tc/g sediment. When Tc was measurable in vadose zone sediments, it was predominantly present as TcO4- in water films associated with fine-grained sediments, with a maximum of 12 % of the total Tc present in the acid-extractable fraction, defined here as the immobile fraction. However, beneath one waste disposal site, where sediments containing minerals with reducing capacity intercepted miscellaneous fission product recovery waste and waste from the bismuth phosphate process, the amount of Tc present in the immobile fraction was 53 % of the total. Characterization of Tc-containing phases present in these field-contaminated sediments for the first time using Tc K-edge X-ray absorption near edge structure spectroscopy revealed that, as well as Tc present as Tc(VII)O4- in pore water associated with fine-grained sediments, Tc was also: (i) physically encapsulated within solid phases precipitated from other waste components and in multi-component phosphate minerals; and (ii) present as mixed Tc(VII)/Tc(IV)/other reduced Tc species in localized reducing zones. These results will be used to develop improved long-term Tc remediation strategies optimized for field application, through stimulation of conditions that enhance Tc attenuation.

1. INTRODUCTION The Hanford nuclear reservation (Washington State, USA), which produced 67 metric tons of plutonium (Pu) for the US Department of Energy (DOE) weapons program between 1943 and


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1989, is partially bordered by the Columbia River and is the most contaminated US nuclear site with the nation's largest environmental clean-up activity.1 When the Hanford Site was operating, spent fuel reprocessing, isotope recovery operations, and associated waste management activities occurred in the center of the site, defined as the Central Plateau (Figure 1). Hanford’s 53 million gallons of high-level radioactive (accounting for 60% of US radioactive high-level waste) and chemical waste are stored in 177 underground tanks in the Central Plateau’s waste management areas (WMA, Figure 1). One third of these tanks are suspected of leaking 1.9-3.8 million liters of tank waste into the environment, resulting in at least 200 square miles of contaminated groundwater that migrates toward the Columbia River. Liquid waste from chemical separations to extract Pu from irradiated uranium (U) fuel rods was also deposited into engineered cribs and trenches, resulting in groundwater plumes (see Figure 1) and a large vadose (unsaturated) zone contaminant inventory.2 Challenges faced by Hanford remediation efforts are exacerbated by the complexity of its geology, biogeochemistry, and plume mixtures. The vadose zone, which can extend up to 100 m, represents a long-term risk as to groundwater since large volumes of contaminated pore water and sediments still exist. One contaminant of particular concern is technetium-99 (99Tc), a highyield thermal fission product of uranium-235 and plutionium-239, and a radionuclide contaminant with high solubility, environmental mobility, and long half-life (213,000 years).



Figure 1: (a) Map of the Central Plateau at Hanford showing waste disposal areas and groundwater interest areas: 200-BP (orange), 200-PO (yellow), 200-UP (sage), 200-ZP (brown); (b) Map of the major contaminant plumes with technetium-99 in yellow (from DOE/RL-201667, Rev. 0)3 To safely, cost-effectively, and efficiently remediate Tc-contaminated vadose zone sediments and groundwater, it is necessary to (i) ascertain the source term and subsequent history of Tc release to develop conceptual transport models; (ii) understand the products of waste-sediment reaction and mechanisms that drive subsurface migration; (iii) determine Tc environmental reaction rates (kinetics); and (iv) evaluate the risk associated with in-ground stability and future migration potential. The chemical speciation of Tc present in the subsurface is a crucial parameter in environmental risk assessment because it determines Tc transport, toxicology, and ultimate disposition.4 Thus, the objective of this work is to provide information on the speciation


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of Tc present in unsaturated sediments within the Central Plateau of the Hanford Site. Both direct measurement of Tc speciation, using state-of-the-art solid phase characterization instruments, and indirect methods, such as sequential extraction protocols, have been performed on Tc-contaminated sediments. These results are discussed in terms of the effects of source term chemistry, geochemical interactions including co-mingled contaminants, and biologically driven transformations on Tc speciation.

This Tc speciation information can be used to aid the

development of long-term remediation strategies. 1.1 Using Source Term History to Identify Potential Tc Hot Spots To understand Tc distribution and speciation at the Hanford Site, historical information on Tc production must be considered. Furthermore, a mass balance is required to establish where the Tc now resides, with an emphasis on its distribution in the unsaturated sediments below storage and disposal facilities. Tc is present in the Hanford Site sediments because of: (i) unplanned discharges in the form of leaks from single shell tanks (SSTs) or their ancillary piping; and (ii) waste intentionally disposed of in near-surface disposal facilities such as cribs, trenches, French drains, and ponds. The chemistry of these source terms is highly variable, including highly alkaline aqueous tank waste, more dilute solutions of variable acidity, and organic waste streams, and may contain other contaminants (NO3-, CrO42-, I-129 and U(VI)) that potentially impact the fate and transport of reduction-oxidation (redox)-sensitive radionuclides, including Tc. Figure 2 shows the current estimate of where Tc produced at Hanford currently resides. The estimate for total Tc produced at Hanford is 32,600 Ci,5 with 26,500 Ci of Tc currently stored in tanks. The rest of the Tc mass balance is less certain. Using historical records, Corbin et al. (2005) made estimates of the inventories of Tc-99 released to the subsurface (~700 Ci total), labeled “Liquid Waste Disposed to Ground” in Figure 2.2 This fraction released into the environment can be



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separated into: (i) cribs, trenches, and ponds (~600 Ci); and (ii) un-planned releases from pipelines

and

SSTs

(~100


Ci).2,

5

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Figure 2. Mass Balance for Tc Produced at the Hanford Site (IHLW – immobilized high-level waste; ILAW – immobilized low activity waste; LLW – low level waste, IDF – integrated disposal facility) In terms of waste type, most of the Tc released emanated from disposal to the BC Cribs region (located in the Inner Area, Figure 1) of: (i) waste from the bismuth phosphate process, used to extract Pu from irradiated U fuel rods; and (ii) wastes containing ferrocyanide, used to recover U


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from bismuth phosphate wastes. The majority of Tc was released to the subsurface prior to 1960, with one large Tc release from the T tank farm (WMA T-TX-TY, Figure 1) in 1973. However, Tc concentrations in waste and groundwater were not measured until the late 1980s due to the difficulty and cost associated with measurement. The total inventory of Tc released to the subsurface at the Hanford site has been estimated from historical records to be ~700 Ci, with ~100 Ci released from SSTs, and the remainder disposed of in the cribs, trenches, and other nearsurface waste sites.2-3 Decades-long groundwater monitoring efforts aid in determining the current location of Tc in the Hanford Site subsurface. The first reported groundwater Tc measurements occurred in 1987, but the Hanford Tc measurement program did not become widespread until 1993. Eventually, site-wide groundwater annual reports began documenting Tc plumes in regions where enough monitoring wells were available to estimate areal extent. These plots have been used to track Tc plume movements with time, and the two largest Tc plumes are associated with: (i) the U cribs in the 200 West Area (200-W, Figure 1); and (ii) the BY cribs located at the northwestern edge of the 200 East Area (200-E, Figure 1).6 Table 1 provides the Tc inventories released to each of the seven regions commonly used to describe the Central Plateau region at the Hanford Site (Figure 1). The BC Cribs region (south of 200-East) has the most Tc inventory (411 Ci) and least liquid waste volume (121 ML) disposed. Thus, it can be expected that vadose sediments and pore water below the BC Cribs would have the highest concentrations of Tc. The leading edge of the plume has reached the water table, although Tc concentrations are below the maximum contaminant level (900 pCi/L), so are not reported in groundwater monitoring.3, 7-8 The region with the second-highest Tc inventory release is the B Complex (WMA B-BX-BY) with 152.4 Ci of Tc. The third-highest Tc inventory (49.82


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Ci) was released from the T Complex (WMA T-TX-TY), and most of the Tc (37.41 Ci in 4.3 ML) was from one tank leak in 1973. Table 1. Tc Disposed/Leaked into Central Plateau2

Location A-AX Complex B Complex BC Cribs C Complex S-SX Complex T Complex U Complex Not captured in this roll upA Total

Tc Total Tc Tc Released to Released (Ci) Cribs/ by Tanks Released Trenches (Ci) (Ci)

Vol of Waste Disposed to Vol of Waste Cribs/trenches Escaped from (ML) Tanks (ML)

9.28 152.4 411 7.97 38.4 49.82 14.29

6.97 10 0 0.56 32.4 44.9 3.57

2.30E+04 1.01E+04 1.21E+02 3.31E+01 6.51E+04 8.35E+03 1.70E+05

1.09E+00 0.842 0 4.26E-02 0.556 5.66 2.84E-01

98.4

7.4E+05 1.02E+06

8.47E+00

3.84 687

2.31 142.4 411 7.41 6 4.9 10.12

588.6

A

Many very low Tc inventory disposal sites and unplanned releases to the Central Plateau were not tabulated, including 3.84 Ci of Tc and 7.4 E+05 ML of very dilute liquid wastes disposed in the Central Plateau. As no Tc measurements were made for groundwater until 1987, it is difficult to assess how much Tc may have entered the Columbia River and traveled downstream to the Pacific Ocean. Available data for total Tc in vadose zone sediments and pore waters beneath the B, T and S-SX tank farms and other disposal sites (cribs, trenches etc.) in the Central Plateau cover less than 1% of the tank farms and disposal sites footprint, thus are too sparse to make a defensible estimate of the mass of Tc that currently resides in the vadose zone.9-11 The amount of Tc currently determined to be in the groundwater, based on annual site-wide groundwater monitoring reports, is ~200 Ci. Thus, a highly conservative estimate would be to assume that none of the Tc has escaped to the Columbia River, and that the remaining ~500 Ci of Tc released to the subsurface is still in the vadose zone.


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1.2 Previous studies to determine Tc speciation in vadose zone sediments Despite years of Tc measurements in Hanford Site vadose zone sediments and groundwater, only total Tc has been reported and there are no direct Tc speciation studies available. There have, however, been several studies on Hanford sediments augmented with Tc, and a limited number of studies employing sequential extractions to determine the chemical form of sedimentassociated Tc. In water-saturated sediments, Tc(VII)O4- can be reduced by magnetite (Fe(III)2Fe(II)O4), Feand Al-oxides in the presence of Fe(II), siderite (Fe(II)CO3), Fe(II)-containing phyllosilicates, and Fe(II)Sx phases, to form a TcO2·xH2O phase.12 Thermodynamically favorable Tc(VII) reduction to Tc(IV) by dissolved Fe(II) in homogeneous aqueous solution is known to be slow.1314

However, when Fe(II) is sorbed onto mineral surfaces, or comprises an intrinsic structural

component of minerals, Tc(VII) reduction kinetics are enhanced, for example Fe(II) sorbed on (oxy)(hydr)oxides of Fe(III), Mn(III/IV), Al(III), as well as silicates.15-17 Tc(VII) is also reduced by structural Fe(II), including that in magnetite and titanomagnetite,13, 18-21 green rust,22 pyrite,23 and clay minerals.16,

24-25

The rates of reduction are dependent on processes such as surface

complexation and Fe speciation.26 Lee et al. (2014) have also shown Tc hot spots in sediments correlated with Fe-containing minerals embedded within a fine-grained phyllosilicate matrix.27 Products of heterogeneous Tc(VII) reduction on Fe- and Mn-bearing mineral surfaces include insoluble crystalline Tc(IV)O2,28-29 amorphous polymeric chains of TcO2·x H2O,15,

30-31

and

Tc(IV) monomers, dimers, and trimers coordinated to Fe-O.13, 15-20, 22, 24, 32-36 The Tc(IV)–Fe(III) molecular speciation form of reduced Tc re-oxidizes more slowly than TcO2·x H2O, the reoxidation resistance of Tc(IV) resulting from shorter chain length.33 Studies have also shown that


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Tc(IV) can be incorporated into corroded steel surfaces,37 and into Fe oxide minerals such as goethite (α-FeOOH) and magnetite (Fe3O4) during co-precipitation reactions, with Tc(IV) directly substituting for Fe(III) in the octahedral site of the crystal structure due to ionic radii similarities.38-41 Relative incorporation energies and lattice bonding environments for chargebalanced Tc(IV) incorporation into Fe3O4 and trevorite (NiFe2O4), evaluated by quantum mechanical methods, show incorporation into Fe3O4 being more energetically favorable than NiFe2O4.42 First principles calculations show that Tc incorporation into goethite and hematite occurs via direct Tc(IV) lattice substitutions for Fe(III), with additional consumption of Fe(III) by reduction to Fe(II) to charge-compensate for the Tc(IV) cation.43-44 Microbial activity, in particular anaerobic respiration of Fe(III)-reducing bacteria to produce biogenic Fe(II),45 also affects the redox state of Tc and, thereby, affects its mobility in the environment. In oxic sediments with low organic carbon content, like those in the vadose zone at the Hanford Site, Tc(VII)O4- is expected to move at pore water velocity. However, even 50 years after the Tc was introduced into the subsurface as described above, it is still present in the vadose zone at relatively shallow depths (6-40 m below ground surface [bgs]). Thus, chemical mechanisms such as Tc-mineral association, may exist for the retention of Tc in Hanford sediments under vadose zone conditions. The acidic and basic waste streams containing the Tc may have altered the mineralogy, potentially affecting Tc speciation and mobility.17 For example, redox reactions between Fe(III) and Tc(IV) at acid pH result in oxidation of Tc(IV) to Tc(VII) with concurrent reduction of Fe(III). In addition, a study of hyperalkaline (~pH 14) waste streams, revealed that Fe(II) released from dissolving iron-bearing minerals was responsible for Cr(VI) reduction in Hanford sediments,46 and Tc reduction.25 Alkaline pore water can cause mineral dissolution, releasing Fe(II) into solution and creating reducing conditions at


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the pore water–mineral interface that result in the reduction and precipitation of Tc in the form of an oxide (TcO2) or sulfide (Tc2Sx).25 As the pH neutralizes, subsequent aluminosilicate or phosphate precipitation can coat the Tc precipitate and prevent re-oxidation.41 Waste containing tri-butyl phosphate (TBP) can increase PO4- concentrations, leading to the formation of phosphate minerals, which could generate a mineral rind and coat Tc, reducing mobility by generating a diffusive barrier or protecting reduced Tc from re-oxidation.47 Precipitation of phosphate mineral phases and high P concentrations associated with Tc in extraction fluids during sequential extraction experiments indicate that Tc species may indeed be associated with phosphate mineral phases.47 Zhao et al. (2002) and Duncan et al. (2012) also found that Tc was retained in apatite in the presence of other reducing agents (Fe(II) and Sn (II)).48-49 Difficult-toextract Tc phases associated with iron oxides and aluminosilicates have been found at locations in the vadose zone with low porosity corresponding with low-conductivity caliche deposits, suggesting that Tc may be retained via geochemical mechanisms.47 It is possible that the mechanism of retention with the caliche layer may involve co-precipitation of TcO4- with calcium carbonate, as with iodate and chromate. It is hypothesized that, if Tc occurs in the solid phase in the subsurface, the conditions that promote Tc precipitation could be used to immobilize it as part of a long-term remediation strategy. In this study, sediments from cores extracted from several waste disposal sites in the 200 Area of the Central Plateau at the Hanford Site have been analyzed by X-ray diffraction (XRD), autoradiography, X-ray fluorescence mapping, and scanning electron microscopy (SEM) to obtain high resolution information on the chemistry and mineralogy of the high-concentration Tc areas identified. Both direct measurement of oxidation state and local coordination environment of sediment-associated Tc using synchrotron X-ray microprobe (XMP), combined


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with X-ray absorption near edge structure (XANES), and indirect methods such as sequential extraction protocols to define the mobile and immobile Tc fractions, were performed on available Tc-contaminated sediments.

2. EXPERIMENTAL SECTION 2.1 Materials Over 30 vadose zone sediment samples with relatively high Tc concentrations were collected from B-BX-BY tank farms (2001), T tank farm and S-SX tank farms (2003), BC cribs (2008) and BY cribs (2016) (Table 2). The archived samples were catalogued and stored in sealed containers under aerobic conditions representative of the conditions in the vadose zone from which they were collected. These samples represent sediments from different geologic units that have been exposed to variety of waste streams, allowing the different mechanisms by which Tc may be immobilized in the subsurface to be investigated, including the effect of localized subsurface conditions (mineralogy, co-contaminants, pH and Eh). In terms of mineralogy, all geologic units contain quartz, plagioclase feldspar and clay minerals (smectite, chlorite and mica). The Hanford formation – H2 unit (H2) consists of sediments with a wide range in grain size from boulder-sized gravel to sane, silty sand, and silt. The Ringold Formation – Member of Taylor Flat (RTaylorFlats) is composed of clay, slit, fine- to coarse-grained sand and gravel. The Cold Creek unit, upper subunit (CCUU), also known as the caliche layer, consists of accumulations of calcite. 48


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Table 2. Hanford site core samples from the 200 Area, Central Plateau Core ID

Section (ft bgs)

Tc in Water/Acid Extraction (ppm)*

Geology

Comments

C4104

20A/20B (115.2116.2) 21A/21B (120.3121.0)

0.36/0.27

RTaylorFlats

9 (86.7) 10 (88.2)

0.06/0.063 0.097/0.11

CCUU

Intercepted waste from the T-106 tank leak. Mostly redox coating wastes, miscellaneous fission produce recovery waste from B Plant, T-Plant bismuth phosphate 1st and 2nd cycle decontamination waste. Variety of waste types resulting in multiple “forms or valence states” for the Tc.

30D (125.2) 31A (132.1) 31G (129.2)

0.01/ND 0.023/0.019 0.035/0.032

CCUU

78A (160.9) 110A (219.5)

0.0008/0.0009 0.0009/0.003

CCUU H2

B1YRJ1 (46.6) B1YRJ2 (49.0)

0.0004/0.0004

H2, sand

13C (104.2105.2)

0.0046/0.0061/0.0 H2, sand

50

C4105 50

B8809 51

S01014 52

C7047 53

C9552 54

0.034/0.079

0.0004/0.0004

Intercepted waste from SX-115 tank leak. Wastes mostly from the redox plant that are highly oxidizing so TcO4- should dominate. Intercepted bismuth phosphate metals waste from BX-102. Highly oxidizing to TcO4- should dominate. Waste stream at BC Cribs and Trenches site was uranium recovery and scavenging wastes from a TBP-based process to recover U from bismuth phosphate waste retrieved from SSTs Intercepted U recovery/Cs-Sr removal waste from BY cribs (ferrocyanide sludge supernatant from TBP in-plant scavenging of Sr-Cs after U recovery)

ND= acid extract not done * Data for Tc in Water/Acid Extraction (ppm) from references in ‘Core ID’ column, with errors stated therein

2.2 X-ray diffraction (XRD) The mineralogy of the bulk sediment samples was determined by XRD techniques. Each bulk sample was prepared for XRD analysis by crushing the sample into a fine powder using a ceramic mortar and pestle. Powders were loaded into zero-background holders and diffraction


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data were collected with a Rigaku MiniFlex II Bragg-Brentano diffractometer using Cu-Kα radiation (λ = 1.5418 Å) and a graphite post-diffraction monochromator. Semi quantification of mineral phases in the bulk sediment samples were determined by the whole pattern fitting technique provided by JADE® XRD pattern processing software and reference spectra from the International Centre for Diffraction Data XRD database. 2.3 Thin Sections Thin sections were prepared using an aluminum holder containing epoxy (Struers EpoFix®) to embed aliquots of the contaminated sediment. The embedded samples were cut and fixed to quartz microscope slides with the epoxy. The sample was cut off the slide with an IsoMetTM 1000 slow speed circular saw and diamond wafering blade (Buehler), leaving ~150 µm thickness of sample on the slide. The sample was then polished to ~50 µm thickness. 2.4 Sequential Extraction A sequential extraction protocol, including (1) 1:1 water extraction; (2) acetic acid extraction for carbonates; (3) oxalic acid for iron oxides; and (4) nitric acid for aluminosilicates, was used to determine which mineral fraction the Tc is associated with.54 Extraction (1) is defined as the mobile Tc fraction, and Extractions (2-4) are defined as the immobile Tc fraction. For the 1:1 water extraction, double-deionized water was mixed with sediment at a ratio of 1:1 dry sediment to water, for 60 minutes; the tube was centrifuged (10 min, 3000 rpm), and liquid was drawn off the top of the sediment and filtered (0.45 µm) for analysis. The acetic acid extraction was conducted on the same sample with the same procedure except with a contact time between sediment and acetic acid (50.66 mL concentrated glacial acetic acid (17.4 mol/L) + 47.2 g Ca(NO3)2•4H2O, pH 2.3, made up to 2.0 liters with deionized water) of 5 days. For the nitric acid


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extraction, nitric acid (8.0 mol/L) was added, used to transfer the residual sediment to a glass beaker, and mixed for 3 hours at 95°C with the sediment; after cooling, the sample was rinsed back into the tube using 3 mL of 8M nitric acid, the tube was then centrifuged (10 mins, 3000 rpm), and liquid was drawn off the top of the sediment and filtered (0.45 µm) for analysis. The extracts were diluted in nitric acid (2 %) and the Tc concentration was measured using a ThermoFisher Scientific X series 2 ICP-MS (analytical method detection limit, taking into account calibration data = 0.01 ppb). Errors associated with extraction were determined by duplicate analyses of sediments. 2.5 Plate Autoradiography Thin sections were imaged by traditional phosphor plate autoradiography. The thin section samples were positioned in an autoradiography cassette against erased GE BAS-IP SR imaging plates and placed in a lead cave for 1 week. The exposed plates were scanned using a GE TyphoonTM FLA 9500 autoradiography scanner. The resulting imagery was normalized by the exposure time to produce maps of radioactivity as counts per hour. To establish: (i) the quantitative nature of autoradiography for Tc; and (ii) that the detection limit was low enough to analyze for Tc in these samples, uncontaminated Ringold sediment was exposed to solutions containing a range of Tc concentrations (0.06 ppb – 6 ppm) with a solid-tosolution ratio of 1 g: 25 mL for 24 hours (following ASTM method C1733-17). All conditions were run in duplicate. The Tc concentration in solution was measured before and after contact with the sediment using ICP-MS (Thermo-scientific X-series 2). The results of the batch contact experiments are given in Table 3. Measurable Tc spiked into the sediment provided loadings between 33 ± 30 µg Tc/g sediment (from the 6000 ppb solution) and 5 ng Tc/g sediment (from


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the 0.6 ppb solution). After reaction, the sediment and Tc solutions were separated, and an airdried sediment aliquot (0.5 g) mounted in epoxy and analyzed with plate autoradiography to determine the level of detection. Table 3 shows that intensity (counts/hour) does correlate with the expected concentrations and that Tc in sediment is measurable down to at least 3 ng Tc/g sediment (see 0.6 ppb solution in Table 3). It should be noted that Tc removal from the 0.6 ppb solution by the sediment was below the method detection limit for ICP-MS (0.01 ppb), and 6 ppb was the lowest starting Tc concentration where a change in solution concentration was measurable. However, Tc was detected on the sediment collected from the 0.6 ppb solution by autoradiography (Figure S1). Table 3. Comparison of the amount of Tc removed by the uncontaminated Ringold sediments after 24 h batch testing Avg. Mass of Tc Autoradiography Starting Tc Tc Loading on in Radiography intensity (counts/hour) Concentration in Sediment Sample (µg)b Solution (µg Tc/ g soil)a (ppb) 6000 33.144 ± 31.394 8.268 155.30 600 0.661 ± 0.461 0.165 N/A 60 0.106 ± 0.008 0.027 N/A 6 0.005 ± 0.004 0.001 29.65 0.6 ND < 0.003 11.43 0.06 ND 11). Quantification of composition at specific locations was performed using peak to peak ratios, in lieu of elemental standards. 2.7 Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) Thin sections were initially loaded into the electron microscope, QuantaTM 3G FEI, and were exposed to a plasma cleaning treatment that removed the hydrocarbon residues remaining on the surface after sample preparation. Afterwards each thin section was carbon coated by applying a 10-15 nm thick C-layer using sputter deposition. The morphology of individual grains, their chemical composition, and the composition of selected areas of interest within grains was investigated with SEM-EDS using an Everhart Thornley secondary detector and a low voltage, high contrast back scattering detector. The SEM-EDS spot measurements and compositional mapping was collected by applying a 2.7 nA current and a 30 kV voltage. The spot analysis showed variation in C content within the selected areas. The high C values seemed associated with the epoxy background, due either to electron beam probing surrounding areas outside of smaller grains or to whether the grains were located directly on the surface or buried underneath the thin sections surface. 2.8 X-ray absorption spectroscopy


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Aliquots of the most concentrated Tc sediment thin sections, and the uncontaminated Ringold sediment after exposure to a 6 ppm Tc solution, were sent to the Advanced Photon Source (APS) at Argonne National Laboratory for XANES spectroscopy, to determine the oxidation state of sediment-associated Tc. Thin sections were first characterized by synchrotron XMP fluorescence imaging on beamline 20-ID at the APS. XMP fluorescence images were collected for Tc, U, Zr, Nb, Sr, Fe, Ti, Cu, Zn, Rb and Cr with a beam size of 2 x 3.5 µm, and at an energy above the Tc edge (22500 eV). A Si (111) monochromator provided an energy resolution of 3 eV at the Tc K edge. X-ray fluorescence maps of the thin sections were collected with a step size of 5 µm and used to choose points for subsequent XANES measurements at the Tc K-edge and the U L3-edge. Tc and U data were taken in fluorescence mode with a Mo foil used for online energy calibration. The XANES data were analyzed using the Athena interface to the IFEFFIT program package.55 2.9 Column Leach Experiment Saturated column experiments were conducted to investigate Tc(VII) release from fieldcontaminated sediments during reactive transport of aerobic synthetic Hanford groundwater (pH 8.05, Table S1). A polyvinyl chloride column with inner diameter of 2.4 cm and length of 9.5 cm was packed uniformly with C4104-20 A sediment. Porous plates (0.25 cm thick with 10 µm pore diameter) were used to prevent sediment particles from blocking the outlet tubing. The column was maintained at room temperature (~22°C) and was initially saturated with deionized water before the synthetic groundwater was injected. An AVI MICRO 210A infusion pump (3M, St. Paul, MN) controlled up-flow through the column with a flow rate of 0.0294 mL min-1, resulting in a fluid residence time of 12.3 h. The column effluent was collected, and a liquid scintillation analyzer (TRI CARB, 25550 TR/LL, Packard) was used to measure Tc concentrations, a Br


19


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combination ion selective electrode (Accumet) was used to measure Br tracer concentrations, and frequent pH measurements were made. The experiment was run until Tc was no longer detected in the effluent (liquid scintillation counting has a detection limit of 1.65×10-9 mol L-1 and a limit of quantification of 5.5 ×10-9 mol L-1).45 3. RESULTS AND DISCUSSION 3.1 Sediment screening by autoradiography and Tc sequential extraction To select sediment samples most likely to contain solid Tc phases, a screening process was performed using both sequential Tc extraction (Table 4) and autoradiography analysis of sediment thin sections. Tc concentrations (8 M nitric acid extract) in sediments from SX tank farm (B8809-31G, -30D and -31A) ranged from 0.0118-0.0347 µg/g and the Tc was mostly extractable in the aqueous phase. This borehole intercepted highly oxidizing waste from the redox process, so it is likely that the Tc would remain mostly oxidized as TcO4- in waste sent to the SX tank farm. These sediments are from the calcareous Cold Creek Unit, and in one sample (B8809-31A) a significant fraction of the Tc is acetic acid extractable, suggesting the potential for coprecipitation of TcO4- with calcium carbonate (CaCO3), as occurs with iodate (IO3-) and chromate (CrO4-).56 For the T tank farm samples, sediments from C4105 (9 and 10) had low Tc concentrations (0.0115-0.0147 µg/g), but the sediments from C4104 had relatively high Tc concentrations (0.0437-0.4561 µg/g) and Tc is present in all four extracts, suggesting multiple forms of Tc are present in the sediment from borehole C4104. Approximately 115,000 gallons of radioactive waste fluids leaked into the vadose zone sediments under tank 241-T-106 in 1973, contaminating


20

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a sediment volume of ~883, 000 ft3 and reaching a depth of 108 ft bgs.57-58 Borehole C4104 was drilled between SSTs within the T Tank Farm. The maximum concentration of Tc was detected at a depth of 116.02 ft bgs, which is sample 20A (see Table 4.23 in Serne et al., 2004).57 Table 5 shows C4104 sequential extract results for samples 20B, 20A, 21B and 21A that cover the depth range 115.25 to 121 ft bgs. We found that water-extractable Tc (mobile fraction) ranged from 25-64 % of the total and with a significant fraction (3-38% of the Tc) remaining in the nitric acid extractable Tc (immobile fraction). BY Crib sediments had low Tc-99 contamination (0.0004-0.013 µg/g) and the sequential extraction results showed that it was exclusively in aqueous or mobile phases. Table 4: Sequential Tc extraction data Extraction (% of total) Sample Name

Water

Acetic acid

Oxalate solution

Nitric acid

T tank farm: C4104-20A C4104-21A C4104-20B C4104-21B C4105-9 C4105-10

64±12 25±5 49±9 44±8 42±8 59±11

24±5 13±2 21±4 19±4 19±4 24±5

8±2 25±5 15±3 12±2 18±3 9±2

3±1 38±7 14±3 24±5 21±4 8±2

SX tank farm: B8809-31G B8809-30D B8809-31A

95±18 100±19 69±13

0 0 25±5

5±1 0 7±1

0 0 0

BX tank farm: S01014-110A S01014-78A

100±19 100±19

0 0

0 0

0 0

BC cribs & trenches: C7047-B1YRJ1 C7047-B1YRJ2

100±19 77±15

0 23±4

0 0

0 0

BY cribs:


21


C9552-13C*

100

0

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0

0

* From Szecsody et al. 201754 In addition to sequential extraction, the sediments were also analyzed using autoradiography. Autoradiography is not specific for Tc but was used to select the sediments that have measurable radioactivity in localized areas (‘hot-spots’). An example of the autoradiography intensity as a function of sequential extraction for a sediment sample from T farm (C4104-21B) is given in Table 5. The most radioactive hot-spots occur in the starting sediment, but some do remain after aqueous extraction and the number of hot-spots decreases with subsequent acid extractions. Table 5: Autoradiography for C9552-13 from the BY cribs and C4104-21B from T tank farm (including after sequential extraction) Sequential extraction

Optical Image

Autoradiography

C9552-13A Starting sediment

C4104-21B Starting sediment


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C4104-21B Water extraction

C4104-21B Acetic acid extraction (carbonates) C4104-21B Oxalic acid extraction (amorphous FeIII oxides) C4104-21B Nitric acid extraction (aluminosilicates, phosphates)

Of the >30 Hanford waste disposal site sediments selected for analysis by autoradiography, most had radioelement concentrations that were below the autoradiography detection limit of 5 mg Tc/g sediment. Based on results from sequential extraction and autoradiography, two sediments were selected for additional Tc solid phase characterization: (i) sediments from the C4104 borehole (~116 ft bgs) under the T tank farm (S03072-20B and -21B); and (ii) samples from the C9552 borehole (~103 ft bgs) under the BY cribs (C9552-13A). These samples were chosen as they have measurable Tc, exhibit hot spots in autoradiography, represent sediments at


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a similar depth that have been exposed to contrasting waste chemistries, and have different Tc speciation as determined indirectly by sequential extraction. 3.2 Solid phase characterization of sediments from beneath T tank farm and BY cribs The available sediments under the T tank farm with relatively high Tc concentrations are sand with minor interbedded silt and are from116 ft bgs. XRD analysis (Figure 3) shows that they are dominated by quartz and plagioclase feldspar and have a significant clay mineral fraction including smectite, chlorite and mica. The presence of mica is of interest in terms of Tc immobilization as analysis of Tc-containing particles isolated from sediments from the Oak Ridge Site, TN, revealed that non-oxidizable Tc(IV) existed as complexes with octahedral Fe(III) within intra-grain domains of 50–100 µm sized, Fe-containing micas.33 The sediments under the BY Cribs with relatively high Tc concentrations are from the Hanford Formation at 103 ft bgs and are mineralogically similar to the T tank farm sediments but contain much more feldspar and significantly fewer clay minerals than the T Tank Farm sediment (Figure 3).


24

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Ringold

21B

13A Quartz Plagioclase Microcline Amphibole Clinochlore Mica Smectite

20

40 2θ [°]

60

80

Figure 3: XRD patterns for sediment sample 13A collected from borehole C9552 (BY Cribs) and from sample 21B collected from borehole C4104 (T Tank Farm) with matching PDF files: Quartz: PDF#00-046-1045 (Quartz, syn); Plagioclase: PDF#98-000-0041 (Albite); Microcline: PDF#98-000-0305 Clinochlore:

(Microcline,

PDF#00-007-0078

K(AlSi3O8);

Amphibole:

(Clinochlore-1MIIb,

PDF#00-023-1405

ferrian);

Mica:

(Edenite);

PDF#98-000-0321

(Muscovite 2M); Smectite: PDF#00-031-0794 (Corrensite)


25


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To understand correlations between hot spots of radioactive and other elements, thin sections of sediments from C9552-13A and C4104-21B were analyzed by µ-XRF and the images overlaid with those from autoradiography. An example of an area from the C4104-21B thin section is given in Figure 4. Some of the radioactive hot spots are associated with areas high in Fe and Cr, which suggests that a possible mechanism for retarding redox-sensitive radionuclides (and chemical contaminants including Cr) involves reduction by ferrous Fe containing minerals and subsequent precipitation of a solid reduced phase. However, some of the radioactive hot spots are not associated with Fe, so there may be multiple retardation mechanisms, even over relatively small spatial scales.

Figure 4: Optical image (A) and µ-XRF map (B) showing Fe (red) and Cr (blue) distributions overlaid autoradiography contours at 10% of the max exposure (green)


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Further analysis of the C4104-21B thin section by SEM-EDS (Figure 5) showed that Cr was associated with Fe oxides, suggesting that the local redox conditions were sufficiently low to reduce Cr(VI) (Equations 3).

° CrVIO

+ 5H + 3e = CrIIIOH + H O E = 1.34V

(3)

Redox conditions may also have been low enough to reduce Tc(VII) according to equation (4) but it can be hypothesized that the reduced Tc did not remain associated with the mineral phase due to: (i) enhanced solubility of reduced Tc as a function of the alkaline pH conditions or ligand complexation; or (ii)

competition from co-contaminants for available sites on the mineral

surface.

TcVIIO + 4H + 3e = TcIVO ∙ H O + 2 − H O E ° = 0.75V

(4)

There was also evidence for U entrained in precipitated phases, possibly carbonates containing Ca and Na. Calcite-sorbed U(VI) has been observed previously in Hanford sediments, and the uranyl cation can substituted into the calcite structure, forming a relatively stable mineral environment.59


27


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Figure 5. SEM images of selected mineral grains present in the C4101-21B sediments with representative EDS analyses SEM-EDS analysis of sediment from C9552-13A (Fig. 6) revealed that the minerals were heavily altered, suggesting that they had previously been exposed to highly alkaline waste streams. Sediments directly below BY crib foot-prints and near-by have been shown to have


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elevated pH values at shallow depths, which were exposed to large volumes of liquid waste.

60

Over time, the native sediments exhibit a buffering capacity, so changes in mineral morphology could have occurred during active disposal (1954-1955) under high pH conditions, with the pH subsequently returning to that of uncontaminated Hanford sediments as evidenced by the recent measurements on C9552 in the BY cribs.54 SEM-EDS analysis of sediments from beneath the BY cribs also provides evidence for the presence of a multi-component phosphate mineral phase incorporating La, Ce, Nd, Th, and traces of Tc (Fig. 6).


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Figure 6. SEM images of selected mineral grains present in the C9552-13A sediments with representative EDS analyses (n.d. = not detected) 3.3 Tc speciation in Hanford sediments 3.3.1 Identification of Tc hotspots using XMP maps XMP maps of Hanford sediment aliquots were used to identify possible Tc hotspots. XMP maps for the BY Crib sample (C9552-13A) indicate that, on the scale measured (2-µm spot size with 5-µm steps), the Tc is not concentrated in a specific area (Figure 7). For example, it is not associated with Fe and Cr, suggesting that it has not been stabilized as insoluble TcO2 by ferrous iron-bearing minerals in the sediment. There is, however, an accumulation of elements associated with the waste chemistry (U and Th) where Tc was also measurable. Figure 7 also


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shows the presence of very high concentrations of Zr in a few particles, likely ZrO2, which was representative of many of the areas analyzed. The 1954-1955 waste pre-dates the reprocessing of Zr-clad fuel (pre-mid-1960s fuel was clad within Al metal) so zircaloy fuel cladding does not represent a source term for Zr.61 In addition, Zr present in tank waste as a fission product from the fission of U and Pu would predominantly be in the insoluble sludge component that settles in the tanks due to the relative insolubility of Zr-bearing phases and only a few percent of Zr would remain in supernatants cascaded over into the BY Cribs.62 Therefore, the small Zr-containing particles in the sediments may be related to the source term but are likely naturally occurring ZrO2.


31


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Figure 7: X-ray fluorescence microprobe analyses of sediments from C9552-13A showing Tc, U, Cr, Fe, Th and Zr distribution


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XMP maps for the T tank farm sample (C4104-21B) are shown in Figure 8. These maps provide evidence that Tc is not incorporated into the Fe-bearing mineral but is present around the exterior of the particle. Measurable Tc XANES was collected from spot 1 (bottom left corner, Figure 8) and U XANES was collected from a U hot spot.

Figure 8: X-ray fluorescence microprobe analyses of sediments from C4104-21B showing Tc, U, Cr and Fe distribution


33


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3.3.2 Determination of Tc speciation using Tc K-edge XANES spectroscopy Tc K-edge XANES spectra were collected for sediments from C9552-13A, C4104-20B and C4104-21B, representing the first XANES data on Tc present in the waste interacting with Hanford sediments, i.e. without additional Tc augmentation in the laboratory (Figure 9). Each Tc spectrum is shown in Figure 9 and represents the average of three replicate scans smoothed using a boxcar bin size of 5. Even at the low Tc concentrations measured in the Hanford sediment samples, it is apparent from the line shape of the processed Tc K-edge XANES spectra that Tc is present predominantly as TcO4- when compared to the TcO4- reference spectrum. This visual observation is confirmed by linear combination analysis (LCA) in Athena using three Tc standards, pertechnetate adsorbed on resin (TcO4-), TcO2·x H2O, and Tc(CO)3(H2O)2(OH).30, 63 Results from LCA are shown in Table 6. Each sample spectrum was initially fit by equally distributing the fractions of the three Tc standards (i.e., 0.33 for each standard). For all samples, TcO4- was best fit to the sample spectra with this initial fitting approach; however, for comparison all samples were also fit with initial preference towards Tc(I) or Tc(IV) species. These forced LCA fits were performed by setting either the TcO2·xH2O or Tc(CO)3(H2O)2(OH) standard fraction equal to 1 and the remaining two standards equal to 0. For each fit scenario, the F(χ2) value was calculated relative to the best fit for each sample (those fits favoring TcO4-). Forcing TcO2·xH2O or Tc(CO)3(H2O)2(OH) as the predominant phase for samples 13A and 20B results in a relatively large F(χ2) value, ranging from 107 to 366 with lower values observed for TcO2·xH2O forced fits. However, the F(χ2) values associated with TcO2·xH2O and Tc(CO)3(H2O)2(OH) forced fits for sample 21B were only 9 and 12, respectively, suggesting less certainty that the Tc speciation in sample 21B is predominantly TcO4-.


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Figure 9. Tc XANES spectra measured for Hanford sediments 13A, 20B, and 21B (black lines). No more than three scans were collected at any one point to limit exposure to the beam. Linear combination analysis (LCA) was performed for each sample using standards TcO4- (blue), TcO2·xH2O (red), and Tc(CO)3(H2O)2(OH) (purple).30,

63

The LCA fits overlay the sample

spectra in grey for each sample. Table 6. Tc XANES LCA Fit Results for Samples 13A, 20B, and 21B Sample Initial Fit/Forced Tc(I) or Tc(IV) Tc(IV) [as TcO2·xH2O]

13A

13A

13A

20B

20B

20B

21B

21B

21B

Initial

Forced Tc(IV)

Forced Tc(I)

Initial

Forced Tc(IV)

Forced Tc(I)

Initial

Forced Tc(IV)

Forced Tc(I)

0

1

0

0

1

0

0

1

0


35


Tc(VII) [as TcO4-] 1 0.05 0.04 Tc(I) [as 0.03 0 1 Tc(CO)3(H2O)2(OH)] R Factor 0.13 0.46 0.27 χ2 1.65 5.92 3.54 Reduced χ2 0.02 0.06 0.04 F(χ2) 0 108 243 F(χ2) = (χ2fit - χ2best fit)/(Reduced χ2best fit); F(χ2)best fit = 0

Page 36 of 53

0.71

0.07

0.02

1

0.27

0.24

0.29

0

1

0.25

0

1

0.13 1.41 0.01 0

0.62 6.88 0.07 107

0.27 3.01 0.03 366

0.43 14.71 0.16 0

0.49 16.59 0.18 9

0.47 15.94 0.17 12

Re-evaluating the sample XANES spectra by visual observation shows less agreement between 21B relative to 13A and 20B spectra and allows room for argument that the Tc edge is slightly shifted to lower energy, again suggesting the presence of reduced Tc. This shift could be the result of the dynamic chemistry observed in the T tank farm area, which could have areas of more reducing conditions capable of reducing Tc(VII) to Tc(IV), Tc(I), or other reduced Tc species and facilitating Tc immobilization within secondary mineral phases as they formed. The TcO4- anion would not sorb to negatively charged mineral surfaces but, given the close association with the Fe-bearing particle, the presence of Tc could be due to initial reduction of the Tc(VII) by Fe(II), as the reducing waste stream moved through the unsaturated Ringold Formation. Fe(II)-bearing mineral phases present in both the Ringold and Hanford Formation, including phyllosilicates, pyrites, magnetite and siderite, have been shown to act as reservoirs of reactive electron equivalents that can reduce Tc(VII)O4-, in response to favorable local redox conditions.12-15,

19-21, 64

Further evidence for the potential reduction of Tc(VII)O4- by Fe(II)-

bearing minerals is provided by XMP maps of the Fe and Tc Kα emission lines (Fig. S2A-C) and Tc K-edge XANES spectroscopy (Fig. S2D) for the uncontaminated Ringold sediment after exposure to a 6 ppm Tc solution, which was prepared to determine the quantitative nature of autoradiography for Tc (Table 3). Even though the experiments were conducted under aerobic conditions, a significant amount of Tc(VII)O4- was removed from solution to form Tc hot spots observable in autoradiography (Fig. S1) and in the Tc XMP map (Fig. S2A). An overlay of the


36

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Tc and Fe XMP maps (Fig. S2C) reveals that the Tc hot spot is also in close association with an Fe particle, and the Tc in the hot spot has been reduced to Tc(IV) associated with an Fe oxide e.g. magnetite, as shown by the Tc K-edge XANES spectrum (Fig. S2D). Given the relatively small energy shift in the Tc K-edge XANES spectrum for 21B, it is likely that most of the reduced Tc was re-oxidized to Tc(VII)O4- over the 30 years between the tank leak and the borehole sampling during which time the nominally oxidizing Hanford vadose zone conditions were restored. However, LCA results from sample 20B, also sourced from the T tank farm, statistically support the presence of pertechnetate with little evidence of co-mingled reduced Tc. The difference in Tc speciation reported here for otherwise similarly sourced samples shows the dynamic regional chemistry of this area and how there remain pockets of sequestered Tc as suggested by sample 21B. The Tc concentrations, and particularly the acidextractable Tc concentrations (Table 4) are the highest of any available vadose zone sediment subjected to tank leaks and are associated with silty sand to sand to sandy gravel lithologies of upper fine-grained Ringold Formation sequence (member of Taylor Flat), which makes up the lower half of the vadose zone within the T Tank Farm.57 The high acid-extractable Tc and the mixed Tc valence state suggest that it may be associated with the sediment and may not travel essentially un-retarded as is generally assumed in fate and transport analyses. Saturated column Tc desorption experiments were conducted to assess Tc release/desorption from Tc-contaminated T tank farm sediments. Fast release from the columns indicated that Tc was predominantly present in the sediment as mobile TcO4- with a Kd of 0, in agreement with similar Tc adsorption-desorption laboratory experiments conducted to evaluate Tc sorption.65-66 Thus, although some portion of Tc is not accessible to water extraction, if the recharge rate is


37


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sufficient, Tc release from these field-contaminated sediments is not retarded based on our desorption column test, resulting in potential future impacts to groundwater. In sediments from the BY Cribs area (C9552-13A), the presence of reduced Tc is unlikely due to the oxidizing nature and elevated pH of waste disposed to the BY Cribs. Tc K-edge XANES data corroborate the extraction data (Table 4), which show that Tc in these BY Crib sediments is present as the TcO4- anion in the pore waste and thus does not sorb to sediment and is completely removed by water extraction. Elevated Tc concentrations (0.013 µg/g) occurred at the top of lowpermeability silt zones (~6-12 inches in thickness) with lower concentrations found beneath in another borehole within the BY Cribs area.5 Based on the large fluxes of liquid disposed of to each BY crib, ponding would be expected when the disposed fluids contacted the native sediments. This ponding likely led to significant lateral flow of the waste fluids into the sediments between the cribs and in the native sediments outside the crib area. Finding similar concentrations in sediment ~100 ft laterally from the crib footprint supports the conclusion that, while there was a strong vertical component to vadose zone flow with mobile contaminants reaching the water table, waste fluids disposed of in the BY cribs spread horizontally, especially along fine-grained lenses in the sand-dominated Hanford formation. These small-scale structures result in the retardation of considerable concentrations of Tc, as TcO4-, in deep vadose zone sediments. Column leach studies with sediments from the same depth as those from which the Tc K-edge XANES data were collected (C9552-13A) have been carried out to determine the processes controlling Tc interactions with vadose sediments and the transport of Tc under natural recharge.54 The column data also suggest that almost all the Tc in BY Crib sediments is present in the native pore water and weakly adsorbed on sediment surfaces as the TcO4- anion.


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However, when comparing Tc speciation to the speciation of comingled contaminants in the same area, some qualitative redox information can be gained and there is evidence for localized reducing conditions. Figure 10 shows XANES spectra for Tc (measured at spot 1, Fig. 7), U (measured at spot 2, Fig. 7) and Th (measured at spot 3, Fig. 7). U L-edge XANES spectra collected on borehole C9552, sample 13A (Figure 10) and uranium LCA fits (Table 7), suggest that reducing conditions were such that U, expected to be present in the oxidizing waste as U(VI), was reduced to U(IV), likely forming UO2. The redox potential for reduction of U(VI) (UO22+ + 4H+ + 2e = U4+ + 2H2O E0 = 0.327) is lower than that for the reduction of Tc(VII) (E0 = 0.782). This apparent anomaly could be explained by the enhanced solubility of reduced Tc as a function of alkaline pH, ligand complexation or soluble Tc(I) complexes, or by the anion exclusion effect. Although under vadose zone conditions, U(VI) is likely present as negatively charged hydroxyl and carbonate species, there are several positively charged uranyl ions that can form, e.g. UO2OH+ and (UO2)3(OH)5+, and stick to mineral surfaces where they could be reduced in measurable quantities.67-68 This is unlikely the case for Tc and the TcO4- anion is repelled by the negatively charged mineral surfaces and thus does not accumulate in sufficient concentrations to be measured or reduced at the sediment particle-pore water film interface.12 In addition, UO2 is less susceptible to re-oxidation relative to reduced species, e.g. Tc(IV)O2·xH2O, in the predominantly oxidizing conditions of the Hanford vadose zone, which could also explain the presence of reduced UO2 comingled with oxidized Tc (as TcO4-). The Th XANES spectrum is consistent with Th(IV)O2 spectra published in the literature.69


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Figure 10. Th (black, left), Tc (black, middle), and U (black, right) XANES spectra for sample 13A. Standards used for LCA fitting are also provided for Tc and U, including TcO2·xH2O (red, middle), TcO4- (blue, middle), UO2 (red, right), and UO2(NO3)2 (blue, right).30 Table 7. U XANES LCA Fit Results for Samples 13A and 20A Sample

13A

20A

UO2 UO2(NO3)2 R Factor χ2 Reduced χ2

1 0.05 0.017 0.456 0.004

1 0.04 0.003 0.073 0.001

To further investigate these areas where contaminants are present in mixed valence states, data from the multichannel analyzer (MCA) for three spots where Tc was measured in Figure 7 are shown in Figure 11. The fact that the spots where Tc was measurable corresponded with the


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presence of many other waste constituents (U, Th, Sr, Y, Nb) suggests a possible mechanism for Tc retardation; the TcO4- anion, although showing little affinity for mineral surfaces, could have been physically encapsulated inside solid phases precipitated from other components present in the waste stream.


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Th

Th

Fe Fe

C

Th Y Sr Th Pb

Th

U

U Tc Sr

Zr Nb

Mo

0

5000

10000 Energy (eV)

15000

20000

Figure 11. MCA spectra to show elements present at three spots in sample 13 where Tc was measurable


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A similar story is found with samples from the T farm area. In Figure 12, the Tc K-edge XANES spectrum collected from C4104-20A is presented alongside the U XANES spectrum and their respective standards used for LCA analysis. Again, while Tc persists in an oxidized state (TcO4-), uranium is present as U(IV), likely UO2.

Figure 12. Tc (black, left) XANES spectrum collected for sample 20A and U (black, right) XANES spectra for sample 20A. Standards used for LCA fitting are also provided for Tc and U, including TcO2·xH2O (red, middle), TcO4- (blue, middle), UO2 (red, right), and UO2(NO3)2 (blue, right).30

4. CONCLUSION Characterizing Tc in available field-contaminated Hanford Site sediments using current stateof-the-art solid phase instruments is challenging because there are few places where Tc is present


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at high enough mass concentrations to be easily speciated. The regions just below cribs, trenches, and SSTs that leaked are generally not sampled to avoid exposing workers to high doses of radiation. Many of these boreholes drilled at the Hanford Site for geochemical and hydrologic characterization of sediments fall outside the footprint of disposal facilities, resulting in the contaminants of concern being present at very low concentrations. Here, selection of over 30 sediments from Hanford waste disposal sites, based on historical information and sediment characterization, for analysis by autoradiography revealed that Tc concentrations were generally below the detection limit of 5 mg Tc/g sediment. In the few cases where significant concentrations of Tc were detected in vadose zone sediments, it was predominantly associated with lenses of low-permeability fine-grained material with high moisture contents, which physically trapped TcO4- in low-mobility pore water. Tc concentrated in these low-permeability fine-grained sediments was mainly water extractable with a maximum of 12 % of the total Tc present in the acid-extractable fraction, defined here as the immobile fraction. However, beneath one waste disposal site (T tank farm), where sediments containing minerals with reducing capacity intercepted miscellaneous fission product recovery waste and waste from the bismuth phosphate process, the amount of Tc present in the immobile fraction was 53 % of the total. In this study, the first Tc K-edge XANES spectroscopy of field-contaminated vadose zone sediments has shown that Tc is predominantly present as Tc(VII)O4- in water films associated with fine-grained sediments. However, XMP and XANES analysis revealed that Tc can also be: (i) physically entrapped in the interstices of poly-mineralogic aggregates of other waste components; (ii) included or incorporated in multicomponent phosphate minerals; and (iii) present as mixed Tc(VII)/Tc(IV)/other reduced Tc phases in very localized reducing zones. This information can be used to develop improved long-term Tc remediation strategies for field


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application, through stimulation of conditions that enhance precipitation and stabilization of Tc in these intrinsically-attenuating phases, for example, in situ generation of phosphate phases.

ASSOCIATED CONTENT Supporting Information. Table: •

Synthetic Hanford groundwater composition

Figures: • •

Plate autoradiography images of Tc-loaded sediments X-ray fluorescence microprobe analyses of uncontaminated Ringold sediment after exposure to Tc solution

AUTHOR INFORMATION Corresponding Author *Email: (C.I.P.) [email protected] ACKNOWLEDGMENT This document was prepared under the Deep Vadose Zone – Applied Field Research Initiative at Pacific Northwest National Laboratory. Funding for this work was provided by the U.S. Department of Energy (DOE) Office of Environmental Management Technology Development. SEM measurements were performed in the Environmental Molecular Science Laboratory, a national user facility supported by the DOE Office of Biological and Environmental Research (OBER) and located at PNNL. Use of the Advanced Photon Source, an Office of Science User Facility operated by Argonne National Laboratory, was supported by the US DOE under


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Contract No. DE-AC02-06CH11357. The authors acknowledge Ben Williams, Steven Baum and Ian Leavy for extractions and ICP-MS measurements. The authors wish to thank Jim McKinley for identifying Tc contaminated sediment samples, and Danielle Saunders and Elsa Cordova for accessing the archived cores to retrieve the samples. The Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for the DOE under Contract DE-AC05-76RL01830. ABBREVIATIONS APS, Advanced Photon Source; bgs, below ground surface, DOE, United States Department of Energy; EDS, X-ray energy dispersive spectroscopy; ICP-MS, inductively coupled plasma mass spectroscopy; LCA, linear combination analysis; MCA, multichannel analyzer; PNNL, Pacific Northwest National Laboratory; SEM, scanning electron microscopy; TBP, tri-butyl phosphate; XANES; X-ray absorption near edge structure; XRD, X-ray diffraction spectroscopy; XMP, Xray microprobe; µ-XRF, Micro X-ray fluorescence spectroscopy

REFERENCES 1. Gephart, R. E., Hanford: a conversation about nuclear waste and cleanup. Battelle Press: 2003. 2. Corbin, R. A.; BC Simpson, B. C.; Anderson, M. J.; Danielson III, W. F.; Field, J. G.; Jones, T. E.; Kincaid, C. T. Hanford Soil Inventory Model; CH2M Hill Hanford Group, Inc.: Richland, WA., 2005. 3. DOE/RL-2016-09 Hanford Site Groundwater Monitoring Report for 2015; US Department of Energy-Richland Operations Office: Richland, Washington, 2016. 4. Batuk, O. N.; Conradson, S. D.; Aleksandrova, O. N.; Boukhalfa, H.; Burakov, B. E.; Clark, D. L.; Czerwinski, K. R.; Felmy, A. R.; Lezama-Pacheco, J. S.; Kalmykov, S. N.; Moore, D. A.; Myasoedov, B. F.; Reed, D. T.; Reilly, D. D.; Roback, R. C.; Vlasova, I. E.; Webb, S. M.; Wilkerson, M. P., Multiscale Speciation of U and Pu at Chernobyl, Hanford, Los Alamos, McGuire AFB, Mayak, and Rocky Flats. Environmental Science & Technology 2015, 49 (11), 6474-6484. 5. Serne, R. J.; Rapko, B. M.; Pegg, I. L. Technetium Inventory, Distribution, and Speciation in Hanford Tanks; Pacific Northwest National Laboratory: Richland, WA, 2014. 6. Group, W. H. C. G. Annual Report for RCRA Groundwater Monitoring Projects at Hanford Site Facilities for 1993; US DOE: Richland, Washington, 1994.


46

Page 47 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7. Serne, R.; Ward, A.; Um, W.; Bjornstad, B.; Rucker, D.; Lanigan, D.; Benecke, M. Electrical Resistivity Correlation to Vadose Zone Sediment and Pore-Water Composition for the BC Cribs and Trenches Area; Pacific Northwest National Laboratory: Richland, Washington, 2009. 8. Freedman, V. L.; Chen, X.; Finsterle, S. A.; Freshley, M. D.; Gorton, I.; Gosink, L. J.; Keating, E.; Lansing, C.; Moeglein, W. A. M.; Murray, C. J.; Pau, G. S. H.; Porter, E. A.; Purohit, S.; Rockhold, M. L.; Schuchardt, K. L.; Sivaramakrishnan, C.; Vesselinov, V. V.; Waichler, S. R., A high-performance workflow system for subsurface simulation. Environmental Modelling & Software 2014, 176–189. 9. R.J., S.; Bjornstad, B. N.; Keller, J. M.; Thorne, P. D.; Lanigan, D. C.; Christensen, J. N.; Thomas, G. S. Conceptual Models for Migration of Key Groundwater Contaminants Through the Vadose Zone and Into the Upper Unconfined Aquifer Below the B-Complex; Pacific Northwest National Laboratory: Richland, WA, 2010. 10. Williams, B. A.; Rohay, V. J. Conceptual Site Models for the 200-DV-1 Operable Unit Waste Sites in the S Complex Area, Central Plateau, Hanford, Washington; CH2M HILL Plateau Remediation Company: Richland, Washington, 2014. 11. Williams, B. A.; Rohay, V. J. Conceptual Site Models for the 200-DV-1 Operable Unit Waste Sites in the T Complex Area, Central Plateau, Hanford, Washington; CH2M HILL Plateau Remediation Company: Richland, Washington, 2015. 12. Icenhower, J. P.; Qafoku, N. P.; Zachara, J. M.; Martin, W. J., The biogeochemistry of technetium: a review of the behavior of an artificial element in the natural environment. American Journal of Science 2010, 310 (8), 721-752. 13. Cui, D. Q.; Eriksen, T. E., Reduction of pertechnetate by ferrous iron in solution: Influence of sorbed and precipitated Fe(II). Environmental Science & Technology 1996, 30 (7), 2259-2262. 14. Zachara, J. M.; Heald, S. M.; Jeon, B.-H.; Kukkadapu, R. K.; Liu, C.; McKinley, J. P.; Dohnalkova, A. C.; Moore, D. A., Reduction of pertechnetate [Tc(VII)] by aqueous Fe(II) and the nature of solid phase redox products. Geochimica et Cosmochimica Acta 2007, 71, 21372157. 15. Peretyazhko, T.; Zachara, J. M.; Heald, S. M.; Jeon, B. H.; Kukkadapu, R. K.; Liu, C.; Moore, D.; Resch, C. T., Heterogeneous reduction of Tc(VII) by Fe(II) at the solid-water interface. Geochimica et Cosmochimica Acta 2008, 72 (6), 1521-1539. 16. Jaisi, D. P.; Dong, H. L.; Plymale, A. E.; Fredrickson, J. K.; Zachara, J. M.; Heald, S.; Liu, C. X., Reduction and long-term immobilization of technetium by Fe(II) associated with clay mineral nontronite. Chemical Geology 2009, 264 (1-4), 127-138. 17. Peretyazhko, T.; Zachara, J. M.; Heald, S. M.; Kukkadapu, R. K.; Liu, C.; Plymale, A. E.; Resch, C. T., Reduction of Tc(VII) by Fe(II) sorbed on Al (hydr)oxides. Environmental Science & Technology 2008, 42 (15), 5499-5506. 18. Farrell, J.; Bostick, W. D.; Jarabek, R. J.; Fiedor, J. N., Electrosorption and reduction of pertechnetate by anodically polarized magnetite. Environmental Science & Technology 1999, 33 (8), 1244-1249. 19. Liu, J.; Pearce, C. I.; Qafoku, O.; Arenholz, A.; Heald, S. M.; Rosso, K. M., Tc(VII) reduction kinetics by titanomagnetite (Fe3-xTixO4) nanoparticles. Geochimica et Cosmochimica Acta 2012, 92, 67–81. 20. Pearce, C. I.; Qafoku, O.; Liu, J.; Arenholz, E.; Heald, S. M.; Kukkadapu, R. K.; Gorski, C. A.; Henderson, C. M. B.; Rosso, K. M., Synthesis and properties of titanomagnetite (Fe3-


47


Page 48 of 53

xTixO4)

nanoparticles: A tunable solid state Fe(II/III) redox system. Journal of Colloid and Interface Science 2012, 387 (1), 24-38. 21. Pearce, C. I.; Liu, J.; Baer, D.; Qafoku, O.; Heald, S. M.; Arenholz, A.; Grosz, A. E.; McKinley, J. P.; Resch, C. T.; Bowden, M. E.; Engelhard, M. H.; Rosso, K. M., Characterization of natural titanomagnetites (Fe3-xTixO4) for studying heterogeneous electron transfer to Tc(VII) in the Hanford subsurface. Geochimica et Cosmochimica Acta 2014, 128, 114–127. 22. Pepper, S. E.; Bunker, D. J.; Bryan, N. D.; Livens, F. R.; Charnock, J. M.; Pattrick, R. A. D.; Collison, D., Treatment of radioactive wastes: An X-ray absorption spectroscopy study of the reaction of technetium with green rust. Journal of Colloid and Interface Science 2003, 268 (2), 408-412. 23. D. Bock, W.; Brühl, H.; Trapp, T.; Winkler, A., Sorption Properties of Natural Suflides With Respect to Technetium. In Scientific Basis for Nuclear Waste Management XII, Lutze, W.; Ewing, R. C., Eds. Materials Research Society: Pittsburgh, Pennsylvania, 1989; Vol. 127, pp 973-978. 24. Jaisi, D. P.; Dong, H. L.; Morton, J. P., Partitioning of Fe(II) in reduced nontronite (NAu2) to reactive sites: Reactivity in terms of Tc(VII) reduction. Clays and Clay Minerals 2008, 56 (2), 175-189. 25. Szecsody, J. E.; Jansik, D. P.; McKinley, J. P.; Hess, N. J., Influence of alkaline cocontaminants on technetium mobility in vadose zone sediments. Journal of Environmental Radioactivity 2014, 135, 147-60. 26. Palmer, D. A.; Meyer, R. E., Adsorption of technetium on selected inorganic ionexchange materials and on a range of naturally occurring minerals under oxic conditions. Journal of Inorganic and Nuclear Chemistry 1981, 43 (11), 2979-2984. 27. Lee, J.-H.; Zachara, J. M.; Fredrickson, J. K.; Heald, S. M.; McKinley, J. P.; Plymale, A. E.; Resch, C. T.; Moore, D. A., Fe (II)-and sulfide-facilitated reduction of 99 Tc (VII) O 4− in microbially reduced hyporheic zone sediments. Geochimica et Cosmochimica Acta 2014, 136, 247-264. 28. Lloyd, J. R.; Sole, V.; Van Praagh, C.; Lovley, D., Direct and Fe (II)-mediated reduction of technetium by Fe (III)-reducing bacteria. Applied and environmental microbiology 2000, 66 (9), 3743-3749. 29. Wildung, R. E.; Gorby, Y. A.; Krupka, K. M.; Hess, N. J.; Li, S.; Plymale, A. E.; McKinley, J. P.; Fredrickson, J. K., Effect of electron donor and solution chemistry on products of dissimilatory reduction of technetium byShewanella putrefaciens. Applied and Environmental Microbiology 2000, 66 (6), 2451-2460. 30. Lukens, J., W. W.; Bucher, J. J.; Edelstein, N. M.; Shuh, D. K., Products of pertechnetate radiolysis in highly alkaline solution: structure of TcO2·H2O. Environmental Science & Technology 2002, 36, 1124-1129. 31. Peretyazhko, T. S.; Zachara, J. M.; Kukkadapu, R. K.; Heald, S. M.; Kutnyakov, I. V.; Resch, C. T.; Arey, B. W.; Wang, C. M.; Kovarik, L.; Phillips, J. L.; Moore, D. A., Pertechnetate (TcO4-) reduction by reactive ferrous iron forms in naturally anoxic, redox transition zone sediments from the Hanford Site, USA. Geochimica Et Cosmochimica Acta 2012, 92, 48-66. 32. Fredrickson, J. K.; Zachara, J. M.; Kennedy, D. W.; Kukkadapu, R. K.; McKinley, J. P.; Heald, S. M.; Liu, C. X.; Plymale, A. E., Reduction of TcO4- by sediment-associated biogenic Fe(II). Geochimica et Cosmochimica Acta 2004, 68 (15), 3171-3187. 33. Fredrickson, J. K.; Zachara, J. M.; Plymale, A. E.; Heald, S. M.; McKinley, J. P.; Kennedy, D. W.; Liu, C.; Nachimuthu, P., Oxidative dissolution potential of biogenic and


48

Page 49 of 53 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


abiogenic TcO2 in subsurface sediments. Geochimica et Cosmochimica Acta 2009, 73 (8), 22992313. 34. Burke, I. T.; Livens, F. R.; Lloyd, J. R.; Brown, A. P.; Law, G. T. W.; McBeth, J. M.; Ellis, B. L.; Lawson, R. S.; Morris, K., The fate of technetium in reduced estuarine sediments: Combining direct and indirect analyses. Applied Geochemistry 2010, 25 (2), 233-241. 35. Lear, G.; McBeth, J. M.; Boothman, C.; Gunning, D. J.; Ellis, B. L.; Lawson, R. S.; Morris, K.; Burke, I. T.; Bryan, N. D.; Brown, A. P., Probing the biogeochemical behavior of technetium using a novel nuclear imaging approach. Environmental Science & Technology 2009, 44 (1), 156-162. 36. Maes, A.; Geraedts, K.; Bruggeman, C.; Vancluysen, J.; Rossberg, A.; Hennig, C., Evidence for the interaction of technetium colloids with humic substances by X-ray absorption spectroscopy. Environmental Science & Technology 2004, 38 (7), 2044-2051. 37. Heald, S. M.; Krupka, K. M.; Brown, C. F., Incorporation of pertechnetate and perrhenate into corroded steel surfaces studied by X-ray absorption fine structure spectrsocopy. Radiochimica Acta 2012, 100, 243−253. 38. Marshall, T. A.; Morris, K.; Law, G. T.; Mosselmans, J. F.; Bots, P.; Parry, S. A.; Shaw, S., Incorporation and retention of 99-Tc(IV) in magnetite under high pH conditions. Environmental Science & Technology 2014, 48 (20), 11853-62. 39. Um, W.; Chang, H.; Icenhower, J. P.; Lukens, W. W.; Jeffrey Serne, R.; Qafoku, N.; Kukkadapu, R. K.; Westsik, J. H., Iron oxide waste form for stabilizing 99Tc. Journal of Nuclear Materials 2012, 429 (1-3), 201-209. 40. Um, W.; Chang, H. S.; Icenhower, J. P.; Lukens, W. W.; Serne, R. J.; Qafoku, N. P.; Westsik, J. H.; Buck, E. C.; Smith, S. C., Immobilization of 99-technetium (VII) by Fe(II)goethite and limited reoxidation. Environmentl Science & Technology 2011, 45 (11), 4904-4913. 41. Saslow, S. A.; Um, W.; Pearce, C. I.; Engelhard, M. H.; Bowden, M. E.; Lukens, W.; Leavy, II; Riley, B. J.; Kim, D. S.; Schweiger, M. J.; Kruger, A. A., Reduction and Simultaneous Removal of 99Tc and Cr by Fe(OH)2(s) Mineral Transformation. Environmental Science & Technology 2017, 51 (15), 8635-8642. 42. Smith, F. N.; Um, W.; Taylor, C. D.; Kim, D. S.; Schweiger, M. J.; Kruger, A. A., Computational Investigation of Technetium(IV) Incorporation into Inverse Spinels: Magnetite (Fe3O4) and Trevorite (NiFe2O4). Environmental Science & Technology 2016, 50 (10), 52165224. 43. Skomurski, F. N.; Rosso, K. M.; Krupka, K. M.; McGrail, B. P., Technetium Incorporation into Hematite (alpha-Fe2O3). Environmental Science & Technology 2010, 44 (15), 5855-5861. 44. Smith, F. N.; Taylor, C. D.; Um, W.; Kruger, A. A., Technetium Incorporation into Goethite (alpha-FeOOH): An Atomic-Scale Investigation. Environmental Science & Technology 2015, 49 (22), 13699-13707. 45. Plymale, A. E.; Fredrickson, J. K.; Zachara, J. M.; Dohnalkova, A. C.; Heald, S. M.; Moore, D. A.; Kennedy, D. W.; Marshall, M. J.; Wang, C.; Resch, C. T.; Nachimuthu, P., Competitive Reduction of Pertechnetate (99TcO4−) by Dissimilatory Metal Reducing Bacteria and Biogenic Fe(II). Environmental Science & Technology 2011, 45 (3), 951-957. 46. Qafoku, N. P.; Ainsworth, C. C.; Szecsody, J. E.; Qafoku, O. S.; Heald, S. M., Effect of coupled dissolution and redox reactions on Cr (VI) aq attenuation during transport in the sediments under hyperalkaline conditions. Environmental science & technology 2003, 37 (16), 3640-3646.


49


Page 50 of 53

47. Jansik, D. P., Physiochemical mechanisms for the transport and retention of technetium. Oregon State University: 2013. 48. Zhao, H.; Awwad, N.; Gasser, M.; Hassan, A.; Moore, R. In Sorption of technetium by hydroxyapatite, Abstracts Of Papers Of The American Chemical Society, American Chemical Society 1155 16TH ST, NW, Washington, DC 20036 USA: 2002; pp U530-U530. 49. Duncan, J.; Hagerty, K.; Moore, W.; Rhodes, R.; Johnson, J.; Moore, R., Laboratory Report On The Reduction And Stabilization (Immobilization) Of Pertechnetate To Technetium Dioxide Using Tin (lI) apatite. Report Number: LAB-RPT-12-00001 Revision 0, Washington River Protection Solutions, LLC, Washington 2012. 50. Serne, R. J.; Bjornstad, B. N.; Horton, D. G.; Lanigan, D. C.; Schaef, H. T.; Lindenmeier, C. W.; Lindberg, M. J.; Clayton, R. E.; Legore, V. L.; Geiszler, K. N.; Baum, S. R.; Valenta, M. M.; Kutnyakov, I. V.; Vickerman, T. S.; Orr, R. D.; Brown, C. F. Characterization of Vadose Zone Sediments Below the T Tank Farm: Boreholes C4104, C4105, 299-W10-196, and RCRA Borehole 299-W11-39; PNNL-14849 Rev. 1; Other: 830403000; TRN: US0806189 United States 10.2172/939046 Other: 830403000; TRN: US0806189 PNNL English; ; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2008; p Medium: ED; Size: PDFN. 51. Serne, R. J.; Bjornstad, B. N.; Lanigan, D. C.; Gee, G. W.; Lindenmeier, C. W.; Clayton, R. E.; Legore, V. L.; O'Hara, M. J.; Brown, C. F.; Last, G. V.; Kutnyakov, I. V.; Burke, D. S.; Wilson, T. C.; Williams, B. A. Characterization of Vadose Zone Sediment: Borehole 299-W2319 [SX-115] in the S-SX Waste Management Area; PNNL-13757-2 Rev. 1; Other: 830403000; TRN: US0806108 United States 10.2172/938577 Other: 830403000; TRN: US0806108 PNNL English; ; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2008; p Medium: ED; Size: PDFN. 52. Serne, R. J.; Last, G. V.; Gee, G. W.; Schaef, H. T.; Lanigan, D. C.; Lindenmeier, C. W.; Lindberg, M. J.; Clayton, R. E.; Legore, V. L.; Orr, R. D.; Kutnyakov, I. V.; Baum, S. R.; Geiszler, K. N.; Brown, C. F.; Valenta, M. M.; Vickerman, T. S. Characterization of Vadose Zone Sediment: Borehole 299-E33-45 Near BX-102 in the B-BX-BY Waste Management Area; PNNL-14083; Other: 820201000; TRN: US0500276 United States 10.2172/15010321 Other: 820201000; TRN: US0500276 PNNL English; ; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2002; p Medium: ED; Size: PDFN. 53. Um, W.; Truex, M. J.; Valenta, M. M.; Iovin, C.; Kutnyakov, I. V.; Chang, H.-s.; Clayton, R. E.; Serne, R. J.; Ward, A. L.; Brown, C. F.; Geiszler, K. N.; Clayton, E. T.; Baum, S. R.; Smith, D. M. Characterization of Sediments from the Soil Desiccation Pilot Test (SDPT) Site in the BC Cribs and Trenches Area; PNNL-18800; Other: 830403000; TRN: US201003%%792 United States 10.2172/971110 Other: 830403000; TRN: US201003%%792 PNNL English; ; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2009; p Medium: ED; Size: PDFN. 54. Szecsody, J.; Truex, M.; Lee, B.; Strickland, C.; Moran, J.; Snyder, M.; Resch, C.; Lawter, A.; Zhong, L.; Gartman, B.; sanders, D.; Baum, S.; Leavy, I.; Horner, J.; Williams, B.; Christiansen, B.; McElroy, E.; Nims, M.; Clayton, R.; Appriou., D. Geochemical, Microbial, and Physical Characterization of 200-DV-1 Operable Unit B-Complex Cores from Boreholes C9552, C9487, and C9488 on the Hanford Site Central Plateau; Pacific Northwest National Laboratory: Richland, Washington, 2017. 55. Ravel, B.; Newville, M., ATHENA, ARTEMIS, HEPHAESTUS; data analysis for X-ray absorption spectroscopy using IFEFFIT. Journal of Synchrotron Radiation 2005, 12 (4), 537– 541.


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56. Truex, M. J.; Szecsody, J. E.; Qafoku, N. P.; Sahajpal, R.; Zhong, L.; Lawter, A. R.; Lee, B. D. Assessment of Hexavalent Chromium Natural Attenuation for the Hanford Site 100 Area; Pacific Northwest National Lab.(PNNL), Richland, WA (United States): 2015. 57. Serne, R. J.; Bjornstad, B. N.; Horton, D. G.; Lanigan, D. C.; Lindenmeier, C. W.; Lindberg, M. J.; Clayton, R. E.; LeGore, V. L.; Geiszler, K. N.; Baum, S. R. Characterization of Vadose Zone Sediments Below the T Tank Farm: Boreholes C4104, C4105, 299-W10-196 and RCRA Borehole 299-W11-39; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2004. 58. Routson, R.; Price, W.; Brown, D.; Fecht, K. High-level waste leakage from the 241-T106 tank at Hanford; Rockwell International Corp., Richland, WA (USA). Rockwell Hanford Operations: 1979. 59. Wang, Z.; Zachara, J. M.; McKinley, J. P.; Smith, S. C., Cryogenic laser induced U (VI) fluorescence studies of a U (VI) substituted natural calcite: Implications to U (VI) speciation in contaminated Hanford sediments. Environmental Science & Technology 2005, 39 (8), 26512659. 60. Serne, R. J.; Bjornstad, B. N.; Keller, J. M.; Thorne, P. D.; Lanigan, D. C.; Christensen, J.; Thomas, G. S. Conceptual Models for Migration of Key Groundwater Contaminants Through the Vadose Zone and Into the Upper Unconfined Aquifer Below the B-Complex; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2010. 61. Reynolds, J. G.; Huber, H. J.; Cooke, G. A.; Pestovich, J. A., Solid-phase zirconium and fluoride species in alkaline zircaloycladding waste at Hanford. Journal of Hazardous Materials 2014, 278, 203-210. 62. Serne, R. J.; Lindberg, M. J.; T. E. Jones, T. E.; Schaef, H. T.; K. M. Krupka, K. M. Laboratory-Scale Bismuth Phosphate Extraction Process Simulation to Track Fate of Fission Products; Pacific Northwest National Laboratory: Richland, Washington, 2007. 63. Lukens, W. W.; Shuh, D. K.; Schroeder, N. C.; Ashley, K. R., Identification of the NonPertechnetate Species in Hanford Waste Tanks, Tc(I)−Carbonyl Complexes. Environmental Science & Technology 2004, 38, 229. 64. Cui, D. Q.; Eriksen, T. E., Reduction of pertechnetate in solution by heterogeneous electron transfer from Fe(II)-containing geological material. Environmental Science & Technology 1996, 30 (7), 2263-2269. 65. Kaplan, D.; Seme, R. Distribution coefficient values describing iodine, neptunium, selenium, technetium, and uranium sorption to Hanford sediments. Supplement 1; Pacific Northwest Lab., Richland, WA (United States): 1995. 66. Kaplan, D.; Parker, K.; Orr, R. Effects of High-pH and High-Ionic-Strength Groundwater on Iodide, Pertechnetate, and Selenate Sorption to Hanford Sediments: Final Report for Subtask 3a; Pacific Northwest National Laboratory, Richland, WA: 1998. 67. Konopka, A.; Plymale, A. E.; Carvajal, D. A.; Lin, X.; McKinley, J. P., Environmental controls on the activity of aquifer microbial communities in the 300 area of the Hanford Site. Microbial ecology 2013, 66 (4), 889-896. 68. Peterson, R. E.; Rockhold, M. L.; Serne, R. J.; Thorne, P. D.; Williams, M. D. Uranium contamination in the subsurface beneath the 300 Area, Hanford site, Washington; Pacific Northwest National Laboratory (PNNL), Richland, WA (US): 2008. 69. Rothe, J.; Denecke, M. A.; Neck, V.; Müller, R.; Kim, J. I., XAFS Investigation of the Structure of Aqueous Thorium(IV) Species, Colloids, and Solid Thorium(IV) Oxide/Hydroxide. Inorganic Chemistry 2002, 41 (2), 249-258.


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Characterizing technetium in subsurface sediments for contaminant

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