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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Mobilization of mercury from contaminated creekbank soils

The industrial use of mercury (Hg) led to the contamination of numerous watersheds worldwide, including the East Fork Poplar Creek (EFPC) in Tennessee, USA. Mercury can accumulate in creek banks and floodplain soils and is mobilized into downstream environments due to erosion from precipitation and flooding. Here, this study aimed to evaluate the geochemical conditions contributing to the release of Hg from contaminated soils in this watershed. Bank soil samples from the EFPC watershed with total Hg concentrations ranging from 27.2 to 1,425 mg·kg −1 were used in a series of batch experiments with artificial creek water at a solid-to-solution ratio of 1:30 to assess Hg release. Additional experiments examined Hg release across different soil size fractions and solid-to-solution ratios, as well as the effect of dissolved organic matter and time on Hg mobilization. Mercury release ranged from 0.011 to 0.17% of the total soil Hg and is correlated with total Hg concentrations. Variations in release among size fractions suggested heterogeneous distribution of labile Hg species. Results indicated two distinct solubility regimes depending on solid-to-solution ratios. Dissolved organic matter enhanced Hg release, and time-dependent experiments showed that changes in mercury speciation could decrease dissolved Hg concentrations over time. Identifying conditions that promote Hg mobilization from contaminated soils improves our understanding of Hg fluxes into downstream environments. Key factors influencing mercury release include soil characteristics, water chemistry, and temporal changes in mercury speciation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Effect of Joining Atmosphere in Transient Liquid Phase Bonding of Inconel 617 Superalloy

In the present paper, transient liquid phase (TLP) bonding of Inconel 617 alloy under the different furnace atmospheres of vacuum, argon gas, and air was investigated. The experiments were carried out at 1408 K (1135 °C) for 300 minutes by using BNi-1 filler metals with different thicknesses of 50 and 100 µm. The microstructure, chemical analysis, shear strength, and microhardness of the resultant joints were studied. After 300 minutes, complete isothermal solidification was obtained for both the interlayers having 50 and 100 µm thicknesses under all the furnace atmospheres. The specimens bonded under vacuum condition showed the highest shear strength, failure energy, and ductility. Also, the joint produced under argon gas atmosphere using 100-µm-thick filler metal showed a good strength and may be acceptable in many applications. However, the specimens bonded under air atmosphere were weak, due to their further cavities and non-dissolved carbides. The presence of non-dissolved carbides in the diffusion-affected zone resulted in increasing the hardness of the base metal near the interface. The carbides were dissolved and the hardness of the diffusion-affected zone was reduced under vacuum condition compared to argon and air atmospheres. The best result was obtained for the specimen joined using the 50-µm-thick interlayer under vacuum atmosphere, with about 95.8 pct joint efficiency.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mechanism of Low-Temperature Reduction Degradation of Alumina-Containing Hematite Solid Solution Below 550 °C

Low-temperature reduction degradation (LTRD) of sinter has an adverse effect on blast furnace permeability, and it is mainly caused by the stress produced in the reduction process of hematite. This stress is strongly influenced by alumina dissolved in hematite crystal lattice. In this work, the experiments were conducted to investigate the effect of alumina dissolved in hematite solid solution (H{sub ss}) on LTRD by reducing H{sub ss} below 550 °C. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and optical microscope have been used to characterize the mass change and mineral change of samples, respectively. Jade software has been used to calculate the micro strain in magnetite for quantitatively studying the change of strain in reducing process. The results show that alumina was unfavorable to the reduction of H{sub ss} on thermodynamics, and the starting reduction temperature of H{sub ss} containing 6.0 mol pct alumina was 28 °C higher than that of pure hematite. According to the calculation on kinetics, the generation rate of stress was accelerated by dissolving alumina into hematite crystal lattice. The apparent activation energy of reduction reaction lowered from 47.89 to 28.07 kJ/mol with the increase of alumina content from 0.0 to 6.0 mol pct. The addition of alumina also increased the stress in the reduction products, and this stress was released in the form of LTRD.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Experimental Study on the Formation of V-Rich Spinel Phase in CaO-SiO{sub 2}-MgO-FeO{sub t}-Al{sub 2}O{sub 3}-V{sub 2}O{sub 3}-P{sub 2}O{sub 5} Slags at 1573 K (1300 °C)

To concentrate vanadium dissolved in steelmaking slag and to separate the obtained vanadium (V)-concentrating phase by a magnetic method, the mineral phases in a CaO-SiO{sub 2}-MgO-FeO{sub t}-Al{sub 2}O{sub 3}-V{sub 2}O{sub 3}-P{sub 2}O{sub 5} system at 1573 K (1300 °C) were characterized by scanning-electron microscopy-energy-dispersive spectroscopy and X-ray diffractometry. When the samples were equilibrated in a pure iron crucible and argon atmosphere, four phases were identified, namely, orthosilicate, V-bearing spinel, wüstite, and a glass phase. The orthosilicate, V-bearing spinel, and glass phase occurred in all samples, whereas wüstite appeared only in samples with a higher basicity or high FeO{sub t} content. The results indicate that the V-bearing spinel phase, which is analogous to Fe{sub 3}O{sub 4}, is a thermodynamically stable phase that is suitable for the enrichment of vanadium dissolved in slags. Further analysis reveals that the increases in contents of FeO{sub t} and MgO in slag favor spinel-phase formation. When the slags are saturated by the wüstite phase, almost all dissolved vanadium can be concentrated in the spinel phase.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lead tolerance and bioremoval by four strains of green algae from Nigerian fish ponds

Heavy metals from industry pose threats to human and environmental health. Microalgae are prime candidates to remove heavy metals from water and soil due to their metal-binding affinities, high growth rates, and contamination tolerance. Strain selection and composition of resulting contaminated biomass must be considered for downstream processing. In this study, we assessed the ability of four microalgae strains (Chlorophyceae) that were isolated from contaminated Nigerian fish ponds to take up dissolved lead at environmentally relevant concentrations (<0.05 mg L -1 – WHO standard). In a microplate assay, all strains grew in the presence of lead, tolerating concentrations up to 60 ppm, though the addition of dissolved lead affected the growth of the four strains. In a photobioreactor assay, all strains demonstrated the ability to take up dissolved lead, with removal efficiencies ranging from 86 to 93%. The concentrations of lead in contaminated biomass, removal efficiencies, and bioconcentration factors were greatest in one of the isolates Chlorella sp. MOW 12. Our results reinforce the fact that live microalgae have a greater biosorption capacity. Lead recovery from freeze-dried biomass using five different reagents showed that a 0.1 M hydrochloric acid solution was the most effective, with 83.4% recovery. We also showed that presence of lead in the culture medium resulted in an increase in the quantity of protein in the biomass. Elemental analysis of lead-bound biomass showed an increase in elements including boron and copper and a decrease in cobalt and sodium. Synergystic and antagonystic effect in uptake of other elements was strain specific, suggesting the possibility of tailored wastewater treatments depending on specific requirements.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Oxygen stress mitigation for microalgal biomass productivity improvement in outdoor raceway ponds

Dissolved oxygen (DO) concentrations at supersaturated levels are commonly observed in outdoor microalgae cultures due to photosynthesis during periods of rapid growth. Paradoxically, the photosynthetically generated oxygen is inhibitory and lowers biomass productivity, therefore, increasing the cost of microalgal biofuels. In this study, photosynthetic rates of Monoraphidium minutum 26B-AM and Scenedesmus obliquus UTEX393, two of the top DISCOVR strains, were compared at three DO levels, 0, 8, and 30 mg L -1 . Increasing DO from 0 to 30 mg L -1 caused a 36.6% and 26.1% reduction in photosynthetic rate for M. minutum 26B-AM and S. obliquus UTEX393, respectively. To improve the outdoor pond biomass productivity of each strain, three oxygen stress mitigation methods were tested. The first method raised the dissolved bicarbonate concentration by an order of magnitude to favor bicarbonate transport into the cell, increasing the CO 2 :O 2 ratio near RuBisCO, thus reducing photorespiration. Although this method increased the observed photosynthesis rate of M. minutum 26B-AM by 26% and S. obliquus UTEX393 by 13% in laboratory testing, it failed to improve biomass productivity under outdoor pond conditions for both strains. The second method added sodium sulfite as an oxygen scavenger to chemically lower the DO concentration in the culture. Chemical reduction of dissolved molecular oxygen did not significantly improve the biomass productivity of M. minutum 26B-AM; however, a 10% improvement in biomass productivity for S. obliquus UTEX393 was observed. The final method sparged cultures with air to strip oxygen out of the liquid medium. This did not improve the biomass productivity of M. minutum 26B-AM, likely due to unfavorable weather conditions during cold season cultivation; however, an improvement of 36% in biomass productivity was achieved for S. obliquus UTEX393 during the warm season cultivation. Of the three tested methods, air-sparging was the most effective and practical for improving outdoor biomass production.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Predictive modeling of CO2 sequestration in deep saline sandstone reservoirs: Impacts of geochemical kinetics

One idea for mitigating the increase in fossil-fuel generated CO{sub 2} in the atmosphere is to inject CO{sub 2} into subsurface saline sandstone reservoirs. To decide whether to try such sequestration at a globally significant scale will require the ability to predict the fate of injected CO{sub 2}. Thus, models are needed to predict the rates and extents of subsurface rock-water-gas interactions. Several reactive transport models for CO{sub 2} sequestration created in the last decade predicted sequestration in sandstone reservoirs of ~17 to ~90 kg CO{sub 2} m{sup -3|. To build confidence in such models, a baseline problem including rock + water chemistry is proposed as the basis for future modeling so that both the models and the parameterizations can be compared systematically. In addition, a reactive diffusion model is used to investigate the fate of injected supercritical CO{sub 2} fluid in the proposed baseline reservoir + brine system. In the baseline problem, injected CO{sub 2} is redistributed from the supercritical (SC) free phase by dissolution into pore brine and by formation of carbonates in the sandstone. The numerical transport model incorporates a full kinetic description of mineral-water reactions under the assumption that transport is by diffusion only. Sensitivity tests were also run to understand which mineral kinetics reactions are important for CO{sub 2} trapping. The diffusion transport model shows that for the first ~20 years after CO{sub 2} diffusion initiates, CO{sub 2} is mostly consumed by dissolution into the brine to form CO{sub 2,aq} (solubility trapping). From 20-200 years, both solubility and mineral trapping are important as calcite precipitation is driven by dissolution of oligoclase. From 200 to 1000 years, mineral trapping is the most important sequestration mechanism, as smectite dissolves and calcite precipitates. Beyond 2000 years, most trapping is due to formation of aqueous HCO{sub 3}{sup -}. Ninety-seven percent of the maximum CO{sub 2} sequestration, 34.5 kg CO{sub 2} per m{sup 3} of sandstone, is attained by 4000 years even though the system does not achieve chemical equilibrium until ~25,000 years. This maximum represents about 20% CO{sub 2} dissolved as CO{sub 2},aq, 50% dissolved as HCO{sub 3}{sup -}{sub ,aq}, and 30% precipitated as calcite. The extent of sequestration as HCO{sub 3}{sup -} at equilibrium can be calculated from equilibrium thermodynamics and is roughly equivalent to the amount of Na+ in the initial sandstone in a soluble mineral (here, oligoclase). Similarly, the extent of trapping in calcite is determined by the amount of Ca2+ in the initial oligoclase and smectite. Sensitivity analyses show that the rate of CO{sub 2} sequestration is sensitive to the mineral-water reaction kinetic constants between approximately 10 and 4000 years. The sensitivity of CO{sub 2} sequestration to the rate constants decreases in magnitude respectively from oligoclase to albite to smectite.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Intrinsic reactivity and dissolution characteristics of tetracalcium aluminoferrite

Tetracalcium aluminoferrite is one of the main phases of Portland cement, the dissolution characteristics of which however have not been fully revealed. This work adopted first-principles calculations and Mössbauer spectroscopy as well as X-ray diffraction analysis to clarify the intrinsic reactivity of different species of tetracalcium aluminoferrite crystals. Ca ions are the most reactive species of tetracalcium aluminoferrite and Al ions are slightly more reactive than Fe ions. Moreover, the tetrahedral Al and Fe ions are more reactive than the octahedral Al and Fe ions. These indicate dissolution characteristics of tetracalcium aluminoferrite crystals, namely, Ca ions dissolve first and the tetrahedral species dissolve faster than the octahedral species. After the initial dissolution, the dissolved ions nucleate and grow on the defective surface of C{sub 4}AF and the C{sub 4}AF residues are fully hydroxylated. The further hydration thereafter becomes the complex dissolution with the nucleation and growth of hydration products.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Effect of oxygen co-injected with carbon dioxide on Gothic shale caprock–CO 2 –brine interaction during geologic carbon sequestration

Co-injection of oxygen, a significant component in CO 2 streams produced by the oxyfuel combustion process, can cause a significant alteration of the redox state in deep geologic formations during geologic carbon sequestration. The potential impact of co-injected oxygen on the interaction between synthetic CO 2 –brine (0.1 M NaCl) and shale caprock (Gothic shale from the Aneth Unit in Utah) and mobilization of trace metals was investigated at ~ 10 MPa and ~ 75 °C. A range of relative volume percentages of O 2 to CO 2 (0, 1, 4 and 8%) were used in these experiments to address the effect of oxygen on shale–CO 2 –brine interaction under various conditions. Major mineral phases in Gothic shale are quartz, calcite, dolomite, montmorillonite, and pyrite. During Gothic shale–CO 2 –brine interaction in the presence of oxygen, pyrite oxidation occurred extensively and caused enhanced dissolution of calcite and dolomite. Pyrite oxidation and calcite dissolution subsequently resulted in the precipitation of Fe(III) oxides and gypsum (CaSO 4 ·2H 2 O). In the presence of oxygen, dissolved Mn and Ni were elevated because of oxidative dissolution of pyrite. The mobility of dissolved Ba was controlled by barite (BaSO 4 ) precipitation in the presence of oxygen. Dissolved U in the experimental brines increased to ~ 8–14 μg/L, with concentrations being slightly higher in the absence of oxygen than in the presence of oxygen. Experimental and modeling results indicate the interaction between shale caprock and oxygen co-injected with CO 2 during geologic carbon sequestration can exert significant impacts on brine pH, solubility of carbonate minerals, stability of sulfide minerals, and mobility of trace metals. The major impact of oxygen is most likely to occur in the zone near CO 2 injection wells where impurity gases can accumulate. Finally, oxygen in CO 2 –brine migrating away from the injection well will be continually consumed through the reactions with sulfide minerals in deep geologic formations.

Carbon sequestration↗
DOE OSTI2022

Chemical and isotopic evolution of flowback fluids from the Utica Gas Shale Play, Eastern Ohio USA

For this work, hydraulic fracturing flowback fluids were collected from two Utica/Point Pleasant well pads in eastern Ohio. One site was in the wet gas zone (UPPW), while the site ~50 km south consisted of four wells on the same pad in the dry gas zone (UPPS). Samples of input fluids also were collected before and during hydraulic fracturing. Flowback fluids are Na-Ca-Cl brines with total dissolved salt (TDS) concentrations that increase over several months from ~100 to 200 g/L. The slightly higher TDS of the dry gas fluids are in part due to recycled flowback used as input fluids, and in part due to lower volume of water used in hydraulic fracturing. Concentrations of most major ions (Ca 2+ , Mg 2+ , Na + , Sr2 + , Fe, Mn, Cl – , Br – ) are similar for the five wells sampled, although small but systematic changes occur in the major element ratios over time. Most notably, an increase in the Sr/Cl ratio corresponds to an increase in the 87 Sr/ 86 Sr ratio in the fluids, suggesting interactions with a more radiogenic Sr source in the subsurface. Dissolved Ba concentrations and Ra activities were different between the two sites, reflecting a high SO 4 2– fluid used at the UPPW site, and water-rock reactions occurring during hydraulic fracturing at the UPPS site. Water oxygen (δ 18 O) and hydrogen (δD) isotopes for input fluids used in the UPPW4 well and fresh water used for the UPPS wells fall on the Global Meteoric waterline (GMWL). Flowback fluids from both sites are relatively enriched in δ 18 O and δD compared to the input, but do not appear to follow a simple mixing trend, suggesting reaction and isotopic exchange with carbonates and fractionation due to imbibition in the rock. Cl isotopes, δ 37 Cl in the FP fluids varied from ~ –0.43 to +0.13‰, the largest variation was observed in the earlier stages of flowback, while in the later stages δ 37 Cl exhibited a small but systematic increase over time, suggesting diffusion control of isotopic composition. Some of the trace species measured (dissolved Fe, Mn, thiosulfate and organic acids) do not follow the same trends as the major ions, suggesting contributions from input fluids, or microbially mediated reactions are exerting control on their concentrations. Input water chemistry exerts an important control on the Sr and Ba concentrations in flowback water. High SO 4 2– in the input fluids used for hydraulically fracturing the wet gas well leads to precipitation of barite-celestite in flowback fluids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

The evaluation of critical rare earth element (REE) enriched treatment solids from coal mine drainage passive treatment systems

Rare earth elements (REE; lanthanides and Y) are essential for the development of clean energy technologies. Global demand for REE is expected to increase sharply in the coming decades, especially for certain energy-critical REE (e.g., Y and Nd), spurring investigations into novel sources of REEs. Polluted mine drainage from eastern U.S. coalfields contains elevated concentrations of dissolved Fe, Al, and Mn and is also enriched in REE by up to three orders of magnitude over unpolluted groundwater. Mine drainage remediation systems, designed to precipitate dissolved metals, can sequester >90% of dissolved REE into the precipitated solids (treatment solids). These solids, landfilled at cost to treatment system operators, are a promising REE source. Passive treatment systems with diverse geochemical environments were sampled to determine REE mobility in these systems and REE concentrations in treatment solids. Passive treatment systems were found to produce middle and heavy REE-enriched solids, relative to the North American Shale Composite, with up to 1950 ppm REE and 55% energy-critical REE. SEM-EDS and synchrotron μ-XRF analysis demonstrate the association of REE with Mn-oxide coatings on limestone from a passive treatment system. Calculated concentration factors indicate that passive treatment systems using natural processes (e.g., drainable limestone beds and vertical flow ponds) concentrate REE into treatment solids approximately three times more effectively compared to active treatment systems using caustic chemical additions (e.g., lime). This study suggests that passive treatment systems effectively concentrate REE into treatment solids and these solids could be an alternative and more environmentally friendly source of REE compared to conventional mining on land or the seafloor. Results of this study can also aid in the design of treatment systems engineered to remove and concentrate critical REE which could provide a financial incentive to treat polluted mine water.

58 GEOSCIENCES↗
DOE OSTI2024

Effect of CO 2 on the water slip flow at silica surfaces for nanometer slit pores of talc

In our previous study, Molecular Dynamics (MD) simulated water flow with no dissolved gas in nanometer slit pores of the hydrophobic talc surfaces revealed a slip length of about 0.5 nm, which is close to the size of “water exclusion zone” but much less than experimental slip length. Atomic Force Microscopy (AFM) imaging confirmed the presence of pancake shape nanobubbles at the hydrophobic talc (001) surface (size from tens to hundreds of nanometers). The effect of CO 2 on water slip flow in talc nanopores is reported to reveal the importance of dissolved gas for confined fluid flow. MD simulated 7 nm CO 2 nanobubbles were found to attach and spread at the talc (001) surface, consistent with the AFM observation. Simulated CO 2 saturated water flow in the slit pores of talc (001) surfaces predicted the generation of CO 2 nanobubbles at the end of the slit pore, due to the stabilization of a CO 2 film at the talc (001) surfaces and a water barrier at the edge surfaces of talc. A “critical thickness” of about 1.5 nm was found for CO 2 nanobubbles to be stabilized at the end of the talc (001) surface. With 1.5 nm CO 2 nanobubbles at the talc (001) surface of a 6 nm slit pore, a water slip length of 1.8 nm was determined. Furthermore, the nanometer slit pore simulations with dissolved CO 2 in water revealed an increased slip length. It is expected that an increased slip length value would be found with an increased CO 2 film thickness.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Phase transformation of oxide film in zirconium alloy in high temperature hydrogenated water

The effect of the variation of the dissolved hydrogen concentration on the oxide phase transformation under high-temperature hydrogenated water conditions was investigated using in situ Raman spectroscopy. The Raman spectrum in 50 cm(3)/kg of dissolved hydrogen concentration indicated the formation of monoclinic and tetragonal zirconium oxide at the water-substrate interface. As the dissolved hydrogen concentration decreased to 30 cm(3)/kg, the Raman peaks corresponding to the zirconium oxide phase changed, indicating an oxide phase transformation. And, the results of SEM and TEM analyses were compared with those of in situ analyses obtained for the oxide structure formed on the zirconium alloy.

Kim, Taeho↗
DOE OSTI2024

Electrolytic recovery of metals from lithium battery cathodes in moisture-tolerant molten hydroxide salt

Lithium-ion battery recycling offers an opportunity to develop innovative technologies to close the loop on the battery materials cycle and increase the resilience of the battery supply chain. Here, in this study, we demonstrate a two-step pyroelectrochemical method for producing mixed-metals from lithium-ion cathodes in a molten hydroxide salt. Mixed metal oxides in the form of insoluble lithium-ion cathode materials of LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) and spent lithium-ion battery materials (black mass) were electrochemically reduced to a soluble form and dissolved into a molten hydroxide salt bath. Electrochemical characterization of the process salt indicated accumulation of dissolved transition metals in the salt. A separate cathode was used to produce alloys of Ni, Mn, and Co electrochemically from the dissolved lithium-ion cathode materials. Characterization by scanning electron microscopy fitted with an energy dispersive X-ray spectrometer showed transition metals present in the cathode materials were recovered at the separate cathode. This approach represents a scalable, low temperature pyroelectrochemical process that can potentially reduce the cost and close the loop of battery cathode recycling.

25 ENERGY STORAGE↗
DOE OSTI2020

Manganese: The overlooked contaminant in the world largest mine tailings dam collapse

Manganese (Mn) is an abundant element in terrestrial and coastal ecosystems and an essential micronutrient in the metabolic processes of plants and animals. Mn is generally not considered a potentially toxic element due to its low content in both soil and water. However, in coastal ecosystems, the Mn dynamic (commonly associated with the Fe cycle) is mostly controlled by redox processes. Here, we assessed the potential contamination of the Rio Doce estuary (SE Brazil) by Mn after the world’s largest mine tailings dam collapse, potentially resulting in chronic exposure to local wildlife and humans. Estuarine soils, water, and fish were collected and analyzed seven days after the arrival of the tailings in 2015 and again two years after the dam collapse in 2017. Using a suite of solid-phase analyses including X-ray absorption spectroscopy and sequential extractions, our results indicated that a large quantity of Mn II arrived in the estuary in 2015 bound to Fe oxyhydroxides. Over time, dissolved Mn and Fe were released from soils when Fe III oxyhydroxides underwent reductive dissolution. Due to seasonal redox oscillations, both Fe and Mn were then re-oxidized to Fe III , Mn III , and Mn IV and re-precipitated as poorly crystalline Fe oxyhydroxides and poorly crystalline Mn oxides. In 2017, redox conditions (Eh: -47 ± 83 mV; pH: 6.7 ± 0.5) favorable to both Fe and Mn reduction led to an increase (~880%) of dissolved Mn (average for 2015: 66 ± 130 μg L -1 ; 2017: 582 ± 626 μg L -1 ) in water and a decrease (~75%, 2015: 547 ± 498 mg kg -1 ; 2017: 135 ± 80 mg kg -1 ) in the total Mn content in soils. The crystalline Fe oxyhydroxides content significantly decreased while the fraction of poorly ordered Fe oxides increased in the soils limiting the role of Fe in Mn retention. The high concentration of dissolved Mn found within the estuary two years after the arrival of mine tailings indicates a possible chronic contamination scenario, which is supported by the high levels of Mn in two species of fish living in the estuary. Our work suggests a high risk to estuarine biota and human health due to the rapid Fe and Mn biogeochemical dynamic within the impacted estuary.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2013

Oxidative Dissolution of UO2 in a Simulated Groundwater Containing Synthetic Nanocrystalline Mackinawite

The long-term success of in situ reductive immobilization of uranium (U) depends on the stability of U(IV) precipitates (e.g., uraninite) under oxic conditions. Field and laboratory studies have implicated iron sulfide minerals as redox buffers or oxidant scavengers that may slow oxidation of reduced U(VI) solid phases by oxygen and Fe(III). Yet, the inhibition mechanism(s) and reaction rates of uraninite (UO2) oxidative dissolution by oxic species such as oxygen in FeS-bearing systems remain largely unresolved. To address this knowledge gap, abiotic batch experiments were conducted with synthetic UO2 in the presence and absence of synthetic mackinawite (FeS) under simulated groundwater conditions of pH = 7, PO2 = 0.02 atm, and PCO2 = 0.05 atm (equivalent to total dissolved carbonate of 0.01 M). The kinetic profiles of dissolved uranium indicate that FeS inhibited UO2 dissolution for 51 hr by effectively scavenging oxygen and keeping dissolved oxygen (DO) low. During this time period, oxidation of structural Fe(II) and S(-II) of FeS were found to control the DO levels, leading to the formation of iron oxyhydroxides and elemental sulfur, respectively, as verified by X-ray diffraction (XRD), Mössbauer and X-ray absorption spectroscopy (XAS). After FeS was depleted due to oxidation, DO levels increased and UO2 oxidative dissolution occurred at an initial rate of rm = 1.2 ± 0.4 ×10-8 mol•g-1•s-1, higher than rm = 5.4 ± 0.3 ×10-9 mol•g-1•s-1 in the control experiment where FeS was absent. Soluble U(VI) products were adsorbed by iron oxyhydroxides (i.e. nanogoethite and ferrihydrite) formed from FeS oxidation, which facilitated the detachment of U(VI) surface complexes and more rapid dissolution of UO2. XAS analysis confirmed the adsorption of U(VI) species, and also showed that U(VI) was not significantly incorporated into iron oxyhydroxide structure. This work reveals that both the oxygen scavenging by FeS and the adsorption of U(VI) to FeS oxidation products may be important in U reductive immobilization systems subject to redox cycling events.

Containing↗
DOE OSTI2018

Hydrogen isotope fractionation in the system brucite-water ± NaCl to elevated temperatures and pressures: Implications for the isotopic property of NaCl fluids under geologic conditions

According to the article, a series of hydrothermal experiments have been conducted to determine equilibrium D/H fractionations between brucite and water as a function of temperature (200-600 °C), pressure (2.1-800 MPa), and dissolved NaCl (0-5 molal or 0-22.6 wt%). Along with our previous study, a total of 39 data points show that pressure and dissolved NaCl both increase the D/H fractionation factor at a given temperature. Theoretical treatment allowed a first direct comparison of experimental and theoretical results of brucite-water D/H fractionation at a zero pressure limit. After correcting the pressure effects on brucite D/H partition function ratios (β-factor), the isotope effects of pressure and dissolved NaCl on the D/H β-factor of water were for the first time rigorously evaluated. There is a good linear relationship between the D/H β-factor of the aqueous NaCl solutions and their densities of at a given temperature. A good, pseudo-linear relationship observed between the density of aqueous NaCl solutions and the maximum intensity of the asymmetric OH vibrational frequency of water in turn suggests that this frequency is a fundamental property that determines the β-factor of water at elevated temperatures and pressures. Our study suggests that the density of aqueous solutions (ρ aq-soln ) could be used as a primary parameter to predict the effects of pressure and NaCl compositions on the β-factor of water under geologic conditions encountered in the crust and upper mantle:Δ10 3 1n β wat /Δρ aq-soln = -0.0111 (±0.0012), where Δ is a difference in the value of 10 3 In β wat or ρ aq-soln , and ρ aq-soln in kg m -3 .

bio-inspired, mechanical behavior, carbon sequestr↗