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Nikolla P. Qafoku Odeta QafokuCalvin C. Ainsworth Alice DohnalkovaSusan G. McKinley 《Applied Geochemistry》2007
Hyperalkaline and saline radioactive waste fluids with elevated temperatures from S-SX high-level waste tank farm at Hanford, WA, USA accidentally leaked into sediments beneath the tanks, initiating a series of geochemical processes and reactions whose significance and extent was unknown. Among the most important processes was the dissolution of soil minerals and precipitation of stable secondary phases. The objective of this investigation was to study the release of Fe into the aqueous phase upon dissolution of Fe-bearing soil minerals, and the subsequent formation of Fe-rich precipitates. Batch reactors were used to conduct experiments at 50 °C using solutions similar in composition to the waste fluids. Results clearly showed that, similarly to Si and Al, Fe was released from the dissolution of soil minerals (most likely phyllosilicates such as biotite, smectite and chlorite). The extent of Fe release increased with base concentration and decreased with Al concentration in the contacting solution. The maximum apparent rate of Fe release (0.566 × 10−13 mol m−2 s−1) was measured in the treatment with no Al and a concentration of 4.32 mol L−1 NaOH in the contact solution. Results from electron microscopy indicated that while Si and Al precipitated together to form feldspathoids in the groups of cancrinite and/or sodalite, Fe precipitation followed a different pathway leading to the formation of hematite and goethite. The newly formed Fe oxy-hydroxides may increase the sorption capacity of the sediments, promote surface mediated reactions such as precipitation and heterogeneous redox reactions, and affect the phase distribution of contaminants and radionuclides. 相似文献
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Influence of Carbon and Microbial Community Priming on the Attenuation of Uranium in a Contaminated Floodplain Aquifer 
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下载免费PDF全文 P.J. Mouser L.A. N'Guessan N.P. Qafoku M. Sinha K.H. Williams M. Dangelmayr C.T. Resch A. Peacock Z. Wang L. Figueroa P.E. Long 《Ground water》2015,53(4):600-613
The capacity for subsurface sediments to sequester radionuclide contaminants, such as uranium (U), and retain them after bioremediation efforts are completed is critical to the long‐term stewardship of re‐mediated sites. In U bioremediation strategies, carbon amendment stimulates bioreduction of U(VI) to U(IV), immobilizing it within the sediments. Sediments enriched in natural organic matter are naturally capable of sequestering significant U, but may serve as sources to the aquifer, contributing to plume persistence. Two types of organic‐rich sediments were compared to better understand U release mechanisms. Sediments that were artificially primed for U removal were retrieved from an area previously biostimulated while detrital‐rich sediments were collected from a location never subject to amendment. Batch incubations demonstrated that primed sediments rapidly removed uranium from the groundwater, whereas naturally reduced sediments released a sizeable portion of U before U(VI)‐reduction commenced. Column experiments confirmed that U release persisted for 65 pore volumes in naturally reduced sediments, demonstrating their sink‐source behavior. Acetate addition to primed sediments shifted the microbial community from sulfate‐reducing bacteria within Desulfobacteraceae to the iron‐reducing Geobacteraceae and Firmicutes, associated with efficient U(VI) removal and retention, respectively. In contrast, Geobacteraceae communities in naturally reduced sediments were replaced by sequences with similarity to Pseudomonas spp. during U release, while U(VI) removal only occurred with enrichment of Firmicutes. These investigations stress the importance of characterizing zones with heterogeneous carbon pools at U‐contaminated sites prior to the determination of a remedial strategy to identify areas, which may contribute to long‐term sourcing of the contaminants. 相似文献
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Dian Fiantis Malik Nelson Eric Van Ranst Jusop Shamshuddin Nikolla P. Qafoku 《山地科学学报》2009,6(3):240-254
The Java Island, Indonesia with abundant amount of pyroclastic deposits is located in the very active and dynamic Pacific Ring of Fires. Studying the geochemical weathering indices of these pyroclastic deposits is important to get a clear picture about weathering profiles on deposits resulting from the eruption of Mt. Merapi. Immediately after the first phase of the eruption （March to June 2006）, moist and leached pyroclastic deposits were collected. These pyroclastic deposits were found to be composed of volcanic glass, plagioclase feldspar in various propoitions, orthopyroxene, clinopyroxene, olivine, amphibole and titanomagnetite. The total elemental composition of the bulk samples （including trace elements and heavy metals） was determined by wet chemical methods and X-ray fluorescence （XRF） analyses. Weathering of the pyroelastic deposits was studied using various weathering indices. The Ruxton ratio, weathering index of Parker, Vought resudual index and chemical index of weathering of moist pyroclastic deposits were lower than those of the leached samples, but the alteration indices （chemical and plagioclase） were slightly higher in the moist compared to the leached pyroelastic deposits. 相似文献
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K.M. Campbell R.K. Kukkadapu N.P. Qafoku A.D. Peacock E. Lesher K.H. Williams J.R. Bargar M.J. Wilkins L. Figueroa J. Ranville J.A. Davis P.E. Long 《Applied Geochemistry》2012
Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO4 reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization. 相似文献
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John M. Zachara Calvin C. Ainsworth Jeffrey G. Catalano Odeta Qafoku James E. Szecsody Jeffrey A. Warner 《Geochimica et cosmochimica acta》2004,68(1):13-30
Radioactive core samples containing elevated concentrations of Cr from a high level nuclear waste plume in the Hanford vadose zone were studied to asses the future mobility of Cr. Cr(VI) is an important subsurface contaminant at the Hanford Site. The plume originated in 1969 by leakage of self-boiling supernate from a tank containing REDOX process waste. The supernate contained high concentrations of alkali (NaOH ≈ 5.25 mol/L), salt (NaNO3/NaNO2 >10 mol/L), aluminate [Al(OH)4− = 3.36 mol/L], Cr(VI) (0.413 mol/L), and 137Cs+ (6.51 × 10−5 mol/L). Water and acid extraction of the oxidized subsurface sediments indicated that a significant portion of the total Cr was associated with the solid phase. Mineralogic analyses, Cr valence speciation measurements by X-ray adsorption near edge structure (XANES) spectroscopy, and small column leaching studies were performed to identify the chemical retardation mechanism and leachability of Cr. While X-ray diffraction detected little mineralogic change to the sediments from waste reaction, scanning electron microscopy (SEM) showed that mineral particles within 5 m of the point of tank failure were coated with secondary, sodium aluminosilicate precipitates. The density of these precipitates decreased with distance from the source (e.g., beyond 10 m). The XANES and column studies demonstrated the reduction of 29-75% of the total Cr to insoluble Cr(III), and the apparent precipitation of up to 43% of the Cr(VI) as an unidentified, non-leachable phase. Both Cr(VI) reduction and Cr(VI) precipitation were greater in sediments closer to the leak source where significant mineral alteration was noted by SEM. These and other observations imply that basic mineral hydrolysis driven by large concentrations of OH− in the waste stream liberated Fe(II) from the otherwise oxidizing sediments that served as a reductant for CrO42−. The coarse-textured Hanford sediments contain silt-sized mineral phases (biotite, clinochlore, magnetite, and ilmenite) that are sources of Fe(II). Other dissolution products (e.g., Ba2+) or Al(OH)4− present in the waste stream may have induced Cr(VI) precipitation as pH moderated through mineral reaction. The results demonstrate that a minimum of 42% of the total Cr inventory in all of the samples was immobilized as Cr(III) and Cr(VI) precipitates that are unlikely to dissolve and migrate to groundwater under the low recharge conditions of the Hanford vadose zone. 相似文献
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Nikolla P. Qafoku Calvin C. Ainsworth Odeta S. Qafoku 《Geochimica et cosmochimica acta》2004,68(14):2981-2995
Over 1.6 million liters of radioactive, high-temperature, Al-rich, alkaline and saline high-level waste (HLW) fluids were accidentally discharged from tank leaks onto the sediments at the Hanford Site, Washington. In order to better understand processes that might occur during the migration of HLW through sediments and to estimate their extents, we studied the effects of Al-rich, alkaline and saline solutions on soil mineral dissolution and precipitation during reactive transport. Metal- and glass-free systems were used to conduct miscible-displacement experiments at 50 °C under CO2 and O2 free conditions. Results showed significant release of Si, K, Al, Fe, Ca, Mg, and Ba into the aqueous phase. The transport-controlled release of these elements was time dependent as evidenced by its extent varying with the fluid residence time. Silica initial dissolution rates (6.08 × 10-11 and 5.38 × 10-13 mol m-2 s-1) increased with base concentration, decreased with Al concentration, and decreased with fluid residence time. Aluminum precipitation rates varied in the range from 0.44 to 1.07 × 10-6 mol s-1 and were faster in these column experiments than in previous batch studies. The initial rate constant of Al precipitation reaction was 0.07 h-1 (half-life of 9.9 h at about 3 PV); it increased up to 0.137 h-1 (half-life of 5.1 h at about 20 PV). The precipitates identified with SEM and suggested from the modeling results were mainly NO3-cancrinite. SEM analyses also indicated the formation of sodalite when Al was not present in the leaching solution. In addition, results from modeling suggested the precipitation of brucite, goethite and gibbsite; the latter may precipitate in the presence of high Al concentrations. Aqueous and solid phase transformations caused by base-induced dissolution and subsequent secondary phases precipitation should be important determinants of the fate of contaminants and radionuclides in the vadose zone under alkaline and saline conditions. 相似文献
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