Environ. Sci. Technol. 2006, 40, 3749-3754
Residual Waste from Hanford Tanks 241-C-203 and 241-C-204. 1. Solids Characterization KENNETH M. KRUPKA,* HERBERT T. SCHAEF, BRUCE W. AREY, STEVE M. HEALD, WILLIAM J. DEUTSCH, MICHAEL J. LINDBERG, AND KIRK J. CANTRELL Pacific Northwest National Laboratory, P.O. Box 999, MSIN K6-81, Richland, Washington 99352
Bulk X-ray diffraction (XRD), synchrotron X-ray microdiffraction (µXRD), and scanning electron microscopy/ energy-dispersive X-ray spectroscopy (SEM/EDS) were used to characterize solids in residual sludge from singleshell underground waste tanks C-203 and C-204 at the U.S. Department of Energy’s Hanford Site in southeastern Washington state. Cˇ ejkaite [Na4(UO2)(CO3)3] was the dominant crystalline phase in the C-203 and C-204 sludges. This is one of the few occurrences of cˇ ejkaite reported in the literature and may be the first documented occurrence of this phase in radioactive wastes from DOE sites. Characterization of residual solids from water leach and selective extraction tests indicates that cˇ ejkaite has a high solubility and a rapid rate of dissolution in water at ambient temperature and that these sludges may also contain poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H2O)0-1] as well as nitratine (soda niter, NaNO3), goethite [R-FeO(OH)], and maghemite (γ-Fe2O3). Results of the SEM/EDS analyses indicate that the C-204 sludge also contains a solid that lacks crystalline form and is composed of Na, Al, P, O, and possibly C. Other identified solids include Fe oxides that often also contain Cr and Ni and occur as individual particles, coatings on particles, and botryoidal aggregates; a porous-looking material (or an aggregate of submicrometer particles) that typically contain Al, Cr, Fe, Na, Ni, Si, U, P, O, and C; Si oxide (probably quartz); and Na-Al silicate(s). The latter two solids probably represent minerals from the Hanford sediment, which were introduced into the tank during prior sampling campaigns or other tank operation activities. The surfaces of some Fe-oxide particles in residual solids from the water leach and selective extraction tests appear to have preferential dissolution cavities. If these Fe oxides contain contaminants of concern, then the release of these contaminants into infiltrating water would be limited by the dissolution rates of these Fe oxides, which in general have low to very low solubilities and slow dissolution rates at near neutral to basic pH values under oxic conditions.
* Corresponding author phone: (509)376-4412; fax: (509)376-5368; e-mail:
[email protected]. 10.1021/es051155f CCC: $33.50 Published on Web 05/17/2006
2006 American Chemical Society
Introduction Contractors to the U.S. Department of Energy (DOE) are completing performance assessments to assess the longterm health risks associated with in-place closure of 177 single- and double-shell carbon-steel underground storage tanks containing residual radioactive and toxic wastes at DOE’s Hanford Site in southeastern Washington. The history of operations at the Hanford Site and the key issues associated with the storage and remediation of radioactive wastes and the environmental contamination at this site are discussed elsewhere (1-5). To complete such performance assessments, release models must first be developed for the contaminants of concern for any material remaining in each tank after the principal volume of sludge and supernatant has been removed by chemical treatment, sluicing, and/or pumping campaigns. For the Hanford Site, the primary contaminants of concern for the tanks are typically 99Tc, 238U, 129I, and Cr because of their mobility in the environment coupled with their high toxicities and/or long half-lives (6). Our project team is currently developing source-term models that describe the future release of contaminants if infiltrating waters were to contact the residual solids. These models are based on detailed geochemical testing of residual waste samples and simulate the geochemical interactions between the leachant phase and contaminant-containing solids. In this paper and the companion paper (7), we describe the results of laboratory studies and analyses and the development of a source-term release model for residual sludge from Hanford Tanks 241-C-203 (C-203) and 241-C204 (C-204). The C-200 series consists of four single-shell underground waste tanks (C-201-C-204) in the C Tank Farm in the 200 East Area of the Hanford Site. These tanks are 20 feet in diameter and have a capacity of 55 000 gal when filled to a depth of 24 feet. Johnson (8) summarizes the history of waste transfers into and removals from these tanks, which provides an indication of the types of residual materials that may be present in the tanks. Because of the technical limitations of sludge and supernatant removal processes, some material remained in the tanks after the removal campaigns. Prior to the sampling of residual solids from these tanks by CH2M HILL Hanford Group, Inc. (Richland, WA) in September 2003, no data existed regarding the composition of the solid wastes in the tanks C-203 and C-204. Given the complexity of waste streams and tank transfers from Hanford operations, a contaminant source-term release model could not be developed assuming analogies to the limited information available from Hanford tank simulant studies or prior analyses of sludge and supernatant samples taken from other Hanford tanks. A complete description of all our studies and results for C-203 and C-204 sludge is given in detail in ref 9. Initial testing consisted of fusion analysis and acid digestion to determine the bulk composition of the sludges and water leaching to estimate the soluble portion of the solids. Samples of the unleached sludges and the solids remaining after the water leaching studies were analyzed by bulk X-ray diffraction (XRD) to identify crystalline phases and by scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/ EDS) to characterize the morphologies, phase associations, sizes, and major element constituents of individual particles. Consecutive water replenishment leach tests and selective extraction tests were also completed to further evaluate water leachability and identify solid phases limiting the release of contaminants to solution. In this paper, we present the results of XRD and SEM/EDS studies of the unleached sludge samples collected from tanks C-203 and C-204 during retrieval VOL. 40, NO. 12, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3749
activities and of solids remaining after water leach and selective extractive studies. This paper also contains the results of a limited study using synchrotron-based X-ray microdiffraction (µXRD) to identify U-containing phases in the C-203 water-leached sludge that could not be positively identified by bulk XRD but was thought to be poorly crystalline Na uranate. Cantrell et al. (7) summarize the results from the total fusion analyses, water leaches, selective extractions, and empirical solubility measurements of residual sludges from tanks C-203 and C-204. Cantrell et al. (7) use their results in combination with results from our characterization studies to elucidate the controlling mechanisms for the release of contaminants and to develop a contaminant release model for residual waste in these tanks.
Materials and Methods Sludge Samples. The sludge samples from tanks C-203 (sample ID 19649) and C-204 (sample ID 19650) were collected and provided by CH2M HILL. Each sample represented a composite of several samples, which were collected from two different sampling ports in each tank and combined to produce a single sludge sample to represent each tank (9). Although waste-transfer histories for the C-200 series tanks suggest that the compositions of wastes from these two tanks should be similar, our analyses (9) show that these two composite samples have different chemical compositions. Each sample was highly radioactive and consisted primarily of dark red-brown sludge. A small number of randomly distributed, light colored, submillimeter sized particles were visible in the sludge matrix. During our handling of the waste samples, large aggregates of yellow minerals (subsequently referred to here as “yellow nuggets”) ranging in size from several millimeters to over a centimeter in diameter were discovered embedded in the matrix of the bulk C-203 sludge. Material from one of these nuggets was characterized by XRD and SEM/EDS. To help verify the identification of cˇejkaite in the unleached C-203 and C-204 sludge samples by SEM/EDS, a natural specimen of cˇejkaite from the Svornost Mine at Jachymov in the Czech Republic was purchased from Excalibur Mineral Corp. (Peekskill, NY) and characterized by XRD and SEM/EDS. Powder X-ray Diffraction. Powder XRD techniques developed for examination of radioactive materials were used to identify the crystalline phases present in the unleached and the water-leached sludge samples. This methodology, the XRD unit, and operating conditions used for these analyses, and the procedures used for background subtraction and pattern examination are described in detail in the Supporting Information. Identification of the solid phases in the background-subtracted patterns was based on a comparison of the XRD patterns with the powder diffraction files (PDF-4) published by the Joint Committee on Powder Diffraction Standards (JCPDS) International Center for Diffraction Data (ICDD) (Newtown Square, PA). Synchrotron-Based X-ray Microdiffraction. Synchrotronbased analyses of U-containing particles in water-leached C-203 sludge were completed on beamline ID-20 (PNC-CAT) at the Advanced Photon Source (Argonne National Laboratory, Argonne, IL). Sample mounting and containment methods; beamline operating conditions; and data collection, background subtraction, and analysis procedures are described in the Supporting Information. Large particles containing high U concentrations were first located in the sample mount by using microscanning X-ray fluorescence (µSXRF) to map the distributions of U, Fe, and Pb in sludge sample. X-ray microdiffraction (µXRD) using an X-ray beam with an incoming wavelength of 0.7293 Å was then used to collect diffraction patterns on ∼5-µm diameter areas of relatively large (approximately 20-100 µm), U-rich regions identified by µSXRF. Identification of the solid phases in the 3750
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 12, 2006
FIGURE 1. Background-subtracted XRD patterns for the unleached C-203 bulk sludge and yellow nugget material (based on CuKr radiation, λ)1.5406 Å) shown with XRD patterns for cˇ ejkaite (10), clarkeite (PDF #50-1586), and trigonal Na4UO2(CO3)3 (PDF #11-0081). [The vertical axes for the sludge and database patterns represent the intensity (I) or relative intensity (I/Io) of the XRD peaks.] background-subtracted patterns was based on a comparison of the µXRD patterns with the diffraction patterns in the JCPDS-ICDD database. Scanning Electron Microscopy/Energy-Dispersive X-ray Spectroscopy. Samples of unleached and water-leached C-203 and C-204 sludges and of residual solids that remained at the end of certain extraction tests of sludge and solubility experiments were characterized by SEM/EDS. The instrumentation and operating conditions used for the SEM and EDS analyses are described in detail in the Supporting Information. Each SEM mount was coated with carbon using a vacuum sputter-coater to improve the conductivity of the samples. To help identify particles that contained elements with large atomic numbers, such as U, the SEM was typically operated in the backscattered electron (BSE) mode.
Results and Discussion Powder X-ray Diffraction. The XRD results (Figure 1) indicate that unleached C-203 and C-204 sludges and the yellow nugget material consist primarily of cˇejkaite, Na4(UO2)(CO3)3. There were no major unassigned reflections in the XRD patterns for the unleached C-203 and C-204 sludges or the yellow nugget material, which suggests that these samples did not contain any other crystalline solids present at more than 5-10 wt % of the sample mass. The phase associated with the small, but discernible, broad peak at approximately 5°2θ in the XRD pattern for the unleached C-203 bulk sludge in Figure 1 could not be identified. The patterns in Figure 1 are exact matches to the XRD patterns for cˇejkaite presented in ref 10 and database pattern PDF #51-1474 which is assigned to an “unnamed mineral” with the formula Na4(UO2)(CO3)3. Petr Ondrusˇ (personal communication) at the Czech Geological Survey, Prague, Czech Republic has confirmed that PDF #51-1474 pattern and ref 10, which both cite ref 11 as the source of the mineralogical information, refer to the same mineral with the now accepted name cˇejkaite (10). The yellow nugget material also contains a significant, but undeterminable, mass of noncrystalline component(s) based on the broad XRD peak observed in the as-measured pattern between 10 and 30°2θ, which is characteristic for amorphous solids [Supporting Information, Figure S-1]. The XRD pattern for the yellow nugget material is also consistent with the possible presence of nitratine (soda niter, NaNO3) (PDF #36-1474) at a concentration that is estimated from relative peak heights to be significantly less than 25% of the cˇejkaite concentration. Other Na-U phases previously identified in other Hanford tank sludges, such as Na2U2O7 and clarkeite Na[(UO2)O(OH)](H2O)0-1, were not detected in these sludge
The XRD patterns for the similarly processed C-204 samples were essentially identical to those for the C-203 samples except for the identification of quartz (SiO2) in the 2-week water-leached C-204 sludge. Based on published tank chemistry and characterization information, quartz is not expected to be a component in the wastes. Because quartz is one of the principal minerals in Hanford sediments, its presence in the C-204 sample might have resulted from blowing dust or sediment that fell into the tank during sampling or other tank operation activities.
FIGURE 2. As-measured and background-subtracted XRD patterns (based on CuKr radiation, λ)1.5406 Å) for 2-week water-leached C-203 sludge shown with XRD database pattern for clarkeite (PDF #50-1586). samples by XRD (Figure 1). Na uranate solids have been identified by others in tank sludge materials from the Hanford Site (12). Temer and Villareal (13-15) identified Na diuranate (Na2U2O7) by XRD in sludge samples from Hanford Tanks BX-103, BX-105, and BX-109. Herting et al. (16) observed Na2U2O7 in saltcake from Hanford Tank BY-109 and in residues from water and NaOH washing of saltcake from Hanford Tank S-112. Experiments by Traina et al. (17) showed that mixing 10-3 M UO22+ in a NaOH solution resulted in precipitation of a solid that they identified as “Na2U2O7 (clarkeite)”. The XRD patterns for the 2-week (Figure 2) and 3-month water-leached C-203 samples were identical. No significant quantities of crystalline solids were detected in this sample. C ˇ ejkaite was not observed in the 2-week water-leached sample which indicates that most of the cˇejkaite originally present had dissolved. This material may contain a small amount of clarkeite that is poorly crystalline based on small broad reflections observed in the background-subtracted pattern (Figure 2) at approximately 15, 27, 33, 46, and 49°2θ, which correspond to the five most intense reflections for clarkeite (PDF #50-1586).
Synchrotron-Based X-ray Microdiffraction. µXRD patterns were collected for five U-rich regions in a sample of water-leached C-203 sludge, but only one contained adequate reflections that were suitable for phase identification. Reflections in the µXRD patterns for the other four regions were absent or too weak and/or broad for identification, which indicates that solid material in these areas was mostly amorphous. The µXRD pattern [Supporting Information, Figures S-2 and S-3] with useable reflections was from a U-rich particle sitting on top of a larger Fe-rich region. Comparison of the reflections in the background-subtracted pattern for this area matched well with the database patterns for goethite [R-FeO(OH)] (PDF #29-0713), maghemite (γ-Fe2O3) (PDF #391346), and the Na uranates clarkeite (PDF #50-1586) and/or Na2U2O7 (PDF #43-0347). Identification of the Fe oxides is consistent with the µSXRF map for Fe, which showed Fe-rich concentrations in the region surrounding this particle. Goethite and maghemite were not identified in our “bulk” XRD analysis (based on ∼1-cm2 irradiated areas) of the sludge solids, but their identification is consistent with SEM/EDS analyses (see next section) that revealed the presence of Fe oxides in this sludge material. Although the µXRD pattern for this U-rich particle is consistent with the presence of a Na uranate, it was not possible from this pattern to distinguish between clarkeite and Na2U2O7. Scanning Electron Microscopy/Energy-Dispersive X-ray Spectroscopy. Unleached Samples. The SEM micrographs (Figure 3) [also see Supporting Information, Figure S-4] of the natural specimen of cˇejkaite exhibited hexagonal, acicular crystals consisting of Na, U, O, and C. The micrographs and EDS spectra for these crystals were compared to the morphology and composition determined by SEM/EDS of
FIGURE 3. SEM micrographs of typical crystals present in the natural mineral specimen of cˇ ejkaite (3A) and unleached C-203 bulk sludge (3B). [The digital image number, sample label, and scale bar are shown, respectively, at the bottom left, center, and right of this and all subsequent micrographs. The “bse” label indicates that the micrograph was collected with backscattered electrons. Areas labeled by “eds” identify locations where EDS spectra were recorded, which may be found in appendices in ref 9.] VOL. 40, NO. 12, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3751
FIGURE 4. Backscattered-electron SEM micrographs showing typical particles present in the 2-week water-leached C-203 bulk sludge.
acicular crystals observed in the unleached and yellow nugget material in the C-203 and C-204 sludge samples. Figure 3 shows SEM micrographs for typical particles identified in the unleached C-203 sludge. The unleached sludge contains large quantities of hexagonal, acicular crystals, either as single crystals or aggregates of crystals (Figure 3B), composed of Na, U, O, and C that are consistent with the natural cˇejkaite (Figure 3A). Composition labels included in Figure 3 and subsequent micrographs generally list the metals in decreasing abundance as estimated from the relative heights of the major EDS peaks for each element. Many of the particle aggregates appear to be a random intergrowth of needle- and rodlike crystals of cˇejkaite in a matrix of a nondescript phase composed of Na, N, O (possibly NaNO3), and possibly C. This phase could be an amorphous phase or nitratine (soda niter, NaNO3) as suggested by XRD. SEM/EDS analyses of the unleached C-204 sludge indicates this material is composed primarily of hexagonal acicular crystals of cˇejkaite [Supporting Information, Figure S-5] and a nondescript solid composed of Na, Al, P, O, and 3752
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 12, 2006
possibly C. Within this mix of cˇejkaite needles and an amorphous Na-Al-P-O phase, there were particles, sometimes as aggregates, of an Fe oxide that often contains Cr and Ni. The amount of cˇejkaite crystals was less in the unleached C-204 sludge than in the unleached C-203 sludge, which is consistent with the relative total concentrations of U (9) measured for these bulk solids. The SEM/EDS analyses reveal that the yellow nuggets [Supporting Information, Figure S-6] are also composed primarily of cˇejkaite and possibly nitratine. A large amount of the interstitial areas between the cˇejkaite crystals is composed of Na-O(N(C [Supporting Information, Figure S-6B], which is most likely an amorphous solid and possibly nitratine. It appears to be mostly amorphous but may contain areas of crystalline solid such as the region between the two arrows in the upper right quadrant of Figure S-6B [Supporting Information], which appears to have flat crystal faces. Water-Leached Samples. Figure 4 shows SEM micrographs of typical particles remaining in the 2-week water-leached C-203 bulk sludge. The large, smooth, bright particle in Figure
4A,D is also composed of Na, U, O, and possibly C. Particles of this type were present in the unleached and water-leached C-203 sludge but not in unleached C-204 sludge. Because its morphology is distinctly different from the acicular crystals of cˇejkaite, this solid may represent a second U-containing phase, such as Na2U2O7 or clarkeite. The acicular crystals of cˇejkaite observed in the samples of unleached C-203 bulk sludge and yellow nugget material are absent in the waterleached material, which indicates that cˇejkaite has a high solubility and rapid dissolution rate [see ref 7]. The 2-week water-leached material contains a variety of rounded and pitted particles and aggregates of particles with various compositions, as noted in Figure 4. Most of these phases, except for the one containing U, were not observed in the SEM analyses of unleached C-203 sludge. These particles were likely present in the unleached material but were coated with cˇejkaite crystals and the amorphous-like Na-N-O phase. The U phase likely represents poorly crystalline clarkeite or Na2U2O7, as suggested by the XRD results. There are no apparent major differences between the solid observed in the 2-week and 2-month water-leach experiments of the C-203 bulk sludge. The large rounded U-containing particles present in the unleached and 2-week water-leached C-203 sludge are still present after 2 months of water leaching (9). The SEM analyses do not show any significant differences between samples of the 2-week and 2-month water-leached experiments of C-204 residual tank waste. The numerous acicular crystals of cˇejkaite and ubiquitous presence of the amorphous Na-Al-P-O phase observed in the unleached C-204 sludge disappear after the leaching experiment. The water-leached samples do contain a variety of nondescript particles, many of which have pitted, altered surfaces. These include a Si oxide (probably quartz) (which is consistent with the XRD results), Fe oxide (often as globular or botryoidal aggregates), Na-Al silicate, and a porous material or aggregate of submicrometer particles containing Al, Cr, Fe, Na, Ni, Si, U, P, O, and C (similar to that in Figure 4C). The SEM micrographs of C-204 sludge solids remaining after the 2-month leach tests revealed two dissolution characteristics not previously observed [Supporting Information, Figures S-7 and S-8]. These characteristics have potential implications about aqueous dissolution rates of sludge materials and subsequent release of contaminants. Dark-contrast features [marked by white arrows in Figure S-7 in Supporting Information] in an aggregate particle of botryoidal Fe oxide in leached C-204 sludge appear to be preferential dissolution cavities. These features might also be explained by the presence of another phase that contains lighter elements than the Fe oxide matrix, which would cause their dark contrast in the BSE image. However, when imaged at higher magnification [see insert in the upper right corner of Figure S-7 in Supporting Information], these features appear to have depth, which is more consistent with at least some of them being dissolution cavities. Figure S-8B,C [Supporting Information] shows micrographs of an aggregate of Na-Al-P-O particles partially covered by a coating of Fe oxide observed in residual solid from the 2-month leach test of the C-204 sludge. The existence of these dissolution cavities and Fe-oxide coatings suggest that some contaminant solids may become encapsulated by precipitating Fe oxides and thus be partially isolated from fluids used to treat tank sludge during retrieval or pore water that contacts residual solids remaining in the tanks after decommissioning. Release of contaminants of concern from such assemblages would then be a function of the solubility and dissolution rates of these Fe-oxide particles, which likely include coprecipitated trace metals and in general have low to very low solubilities and slow dissolution rates at near neutral to basic pH values under oxic conditions (18).
Sequential Extraction Samples. SEM/EDS analyses were also completed on particles observed in samples of residual solids from the water-, acetate-, and ethanol-contact and HF/NaF buffer selective extractions of C-204 sludge described in ref 7. The residual solids from these chemical treatments are similar to each other and to the water-leached C-204 sludge. Botryoidal aggregates of Fe oxide were also observed. Figure S-8A [Supporting Information], a SEM micrograph of an Fe-oxide aggregate in residual solid from an HF/NaFbuffer selective extraction of C-204 sludge, shows preferential dissolution features that likely contained one or more unknown phases that were more soluble than the Fe-oxide matrix, especially in the HF/NaF extractant. The solid product remaining at the termination of the solubility experiments (9) with the 1:1 sludge-to-solution ratio was also studied by SEM/EDS. The residual solid still contained large quantities of hexagonal, acicular crystals that are composed of Na, U, O, and C [Supporting Information, Figure S-9]. The morphology and compositions of these acicular crystals are consistent with cˇejkaite. Overall Characterization. Results of these solid-phase characterizations [Supporting Information, Table S-1] are important to the development of source-term release models that describe the release of contaminants when infiltrating water in the future contacts residual solids in these particular underground storage tanks after they are decommissioned. C ˇ ejkaite, poorly crystalline clarkeite (or Na2U2O7), nitratine (and/orpoorlycrystallineNaNO3),goethite,possiblymaghemite, and nondescript Na-Al-P-O(C and Al-Cr-Fe-Na-NiSi-U-P-O(C phases (possibly particle aggregates) are present in the unleached and leached C-203 and C-204 sludges. Because cˇejkaite, poorly crystalline clarkeite (or Na2U2O7), and nitratine (and/or poorly crystalline NaNO3) are abundant in these sludges and contain Na as a key component, these phases are important relative to the release of U. However, they will not be stable when contacted by Hanford groundwater which has significantly lower Na concentration than tank wastes. The presence of Fe oxides (goethite and maghemite) is important to the release to Tc because Fe oxides and Al oxyhydroxides are thought to sequester Tc in tank waste (19). Because no Tc was detected by EDS or µXRF in any of these sludge phases, a conservative (bounding) approach may have to used to estimate a limiting value for the maximum release of Tc from Fe oxides. These solid-phase characterization results may be representative of other Hanford storage tanks that have similar histories of waste transfers and removals. However, until more studies of residual waste are completed, the extent of applicability of these results to residual sludges from other Hanford tanks is not known. Our laboratory is currently continuing similar extensive studies of residual wastes from several other Hanford storage tanks. These studies are in support of performance assessments being completed for DOE by the CH2M HILL to assess the long-term health risks associated with closure of underground storage tanks containing residual radioactive and toxic wastes at the Hanford Site. Our study may be the first documented occurrence of cˇejkaite in radioactive wastes from underground storage tanks at DOE sites. Given the long history of nuclear operations and related waste disposal at DOE facilities, cˇejkaite or its trigonal polymorph may have been physically identified and documented in old technical reports that were not available to us. C ˇ ejkaite was only recently described as a new mineral (10) based on its discovery by Ondrusˇ et al. (11) as a secondary mineral in a U ore deposit in the Czech Republic. C ˇ ejkaite may also have been present as an alteration product of the silicate lava that solidified from the destruction of the Chernobyl reactor core (20). VOL. 40, NO. 12, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3753
Acknowledgments The authors acknowledge M. Connelly, F. J. Anderson, and T. E. Jones at CH2M HILL Hanford Group, Inc. (Richland, WA) for providing project funding and technical guidance. The quality of the manuscript was greatly improved from review comments received from R. J. Serne (PNNL), J. G. Hering (Associate Editor), and three journal reviewers. The authors also thank S. R. Baum, K. M. Geiszler, I. V. Kutnyakov, and R. D. Orr (all of PNNL) for completing the solution analyses. Pacific Northwest National Laboratory is operated for the DOE by Battelle Memorial Institute under Contract DE-AC05-76RL01830. The PNC-CAT project at the Advanced Photon Source is supported by funding from the U.S. Department of Energy Basic Energy Sciences, the University of Washington, Simon Fraser University, and the Natural Sciences and Engineering Research Council (NSERC) of Canada. Use of the Advanced Photon Source is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. W-31-109-Eng38.
Supporting Information Available Methods used for the analyses by powder X-ray diffraction, synchrotron-based X-ray microdiffraction, and scanning electron microscopy/energy-dispersive X-ray spectroscopy; as well as additional XRD results and SEM micrographs. This material is available free of charge via the Internet at http:// pubs.acs.org.
Literature Cited (1) Gephart, R. E. Hanford - A Conversation about Nuclear Waste and Cleanup; Battelle Press: Richland, WA, 2003. (2) NRC (National Research Council). Science and Technology for Environmental Cleanup at Hanford; National Academy Press; Washington, DC, 2000. [Report is available online free to the public in pdf format at http://www.nap.edu/ category.html?id)ev.] (3) NRC (National Research Council). The Hanford Tanks: Environmental Impacts and Policy Choices; National Academy Press: Washington, DC, 1996. [Report is available online free to the public in pdf format at http://www.nap.edu/ category.html?id)ev.] (4) Ahearne, J. F. Radioactive waste: The size of the problem. Physics Today 1997, 50 (6), 24-29. (5) Crowley, K. D. Nuclear waste disposal: The technical challenges. Physics Today 1997, 50 (6), 32-39. (6) Kincaid, C. T.; Bergeron, M. P.; Cole, C. R.; Freshley, M. D.; Hassig, N. L.; Johnson, V. G.; Kaplan, D. I.; Serne, R. J.; Streile, G. P.; Strenge, D. L.; Thorne, P. D.; Vail, L. W.; Whyatt, G. A.; Wurstner, S. K. Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site; PNNL-11800; Pacific Northwest National Laboratory: Richland, WA, 1998. [Report is available online to the public in pdf format at https:// www.osti.gov/src/.] (7) Cantrell, K. J.; Krupka, K. M.; Deutsch, W. J.; Lindberg, M. J. Residual waste from Hanford tanks 241-C-203 and 241-C-204. 2. Contaminant release model. Environ. Sci. Technol. 2006, 40, 3755-3761. (8) Johnson, M. E. Origin of Wastes in C-200 Series Single-Shell Tanks; RPP-15408; CH2MHILL Hanford Group: Richland, WA, 2003. [Report is available online to the public in pdf format at https://www.osti.gov/src/.]
3754
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 12, 2006
(9) Deutsch, W. J.; Krupka, K. M.; Lindberg, M. J.; Cantrell, K. J.; Brown, C. F.; Schaef, H. T. Hanford Tanks 241-C-203 and 241C-204: Residual Waste Contaminant Release Model and Supporting Data; PNNL-14903; Pacific Northwest National Laboratory: Richland, WA, 2004. [Report is available online to the public in pdf format at http://www.pnl.gov/main/ publications/.] (10) Ondrusˇ P.; Ska´la, R.; Veselovsky´, F.; Sejkora, J.; Vitti, C. C ˇ ejkaite, the triclinic polymorph of Na4(UO2)(CO3)3 - A new mineral from Ja´chymov, Czech Republic. Am. Mineral. 2003, 88, 686693. (11) Ondrusˇ, P.; Veselovsky´, F.; Ska´la, R.; Cı´sarova´, I.; Hlousek, J.; Fryda, J.; Vavrı´n, I.; C ˇ ejka, J.; Gabasˇova´, A. New naturally occurring phases of secondary origin from Ja´chymov (Joachimsthal). J. Czech. Geol. Soc. 1997, 42, 77-108. (12) Rapko, B. M.; Lumetta, G. J. Status Report on Phase Identification in Hanford Tank Sludges; PNNL-13394; Pacific Northwest National Laboratory: Richland, WA, 2000. [Report is available online to the public in pdf format at http://www.pnl.gov/main/ publications/.] (13) Temer, D. J.; Villarreal, R. Sludge Washing and Alkaline Leaching Tests on Actual Hanford Tank Sludge: A Status Report; LAUR95-2070; Los Alamos National Laboratory: Los Alamos, NM, 1995. [Report is available online in pdf format at http:// catalog.lanl.gov/F.] (14) Temer, D. J.; Villarreal, R. Sludge Washing and Alkaline Leaching Tests on Actual Hanford Tank Sludge: FY 1996 Results; LAUR96-2839; Los Alamos National Laboratory: Los Alamos, NM, 1996. [Report is available online to the public in pdf format at http://catalog.lanl.gov/F.] (15) Temer, D. J.; Villarreal, R. Sludge Washing and Alkaline Leaching Tests on Actual Hanford Tank Sludge: FY 1997 Results; LAUR97-2889; Los Alamos National Laboratory: Los Alamos, NM, 1997. [Report is available online in pdf format at http:// catalog.lanl.gov/F.] (16) Herting, D. L.; Warrant, R. W.; Cooke, G. A. Identification of Solid Phases in Saltcake from Hanford Site Waste Tanks; HNF11585, Rev. 0 (HNF-EDC-02-12376); Fluor Hanford, Inc.: Richland, WA, 2002. [Report is available online to the public in pdf format at https://www.osti.gov/src/.] (17) Traina, S. J.; Grandinetti, P.; Brown, G. E., Jr.; Ainsworth, C. C.; Szecsody, J. E.; Yamakawa, I.; Prasad, S.; Warner, J.; He, Y.; Catalano, J. Immobilization of Radionuclides in the Hanford Vadose Zone by Incorporation in Solid Phases. 2001 Progress Report; U.S. Department of Energy, Environmental Management Science Program (EMSP): Washington, DC, 2001. [Report is available online to the public in pdf format at https:// www.osti.gov/src/.] (18) Cornell, R. M.; Schwertmann, U. The Iron Oxides. Structure, Properties, Reactions, Occurrences and Uses; WILEY-VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2003. (19) Wakoff, B.; Nagy, K. L. Perrhenate uptake by iron and aluminum oxyhydroxides: An analogue for pertechnetate incorporation in Hanford waste tank sludges. Environ. Sci. Technol. 2004, 38, 1765-1771. (20) Burakov, B. E.; Strykanova, E. E.; Anderson, E. B. Secondary uranium minerals on the surface of Chernobyl ‘Lava’. In Scientific Basis for Nuclear Waste Management XX; Gray, W. J., Triay, I. R., Eds.; Materials Research Society: Pittsburgh, PA, 1997; Vol. 465, pp 1309-1311.
Received for review June 17, 2005. Revised manuscript received February 24, 2006. Accepted March 14, 2006. ES051155F
