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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Recovery of Cs-137 from Electric Arc Furnace Dust - 20562

The present work proposes the Cs-137 recovery from Electric Arc Furnace Dusts (EAFD) by leaching, in order to reduce the volume of radioactive waste to be managed. Leaching tests were performed on different samples of EAFD contaminated with Cs-137. Two leaching methodologies were tested: dynamic and static using as medium distilled water and in some cases NaOH. The results indicate the possibility of recovering Cs-137 from EAFD using the dynamic method; however, the recovery efficiencies of Cs-137 depend on EAFD's chemical composition. The leachates of Cs-137 were quantitatively adsorbed on exchange resins, showing its great potential to isolate or contain the Cs-137 recovery from EAFD. This study shows the feasible to apply the dynamic leaching methodology to recover Cs-137 from EAFD and the use of ion exchange resins for the isolation of removed Cs-137. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Sustainable recovery of critical metals from spent lithium-ion batteries through gluconic acid-based bioleaching: Techno-economic analysis, life cycle assessment and process optimization

Recycling spent lithium-ion batteries (LIB) could potentially bridge the ever increasing supply and demand gap for critical metals and simultaneously facilitate the management of hazardous battery waste. This study investigated the optimization of gluconic acid-based bioleaching technology through design of experiments (DOE), combined with techno-economic analysis (TEA), and life cycle assessment (LCA) with the aim of maximizing the net present value (NPV) and minimizing global warming impacts of the process. Biolixiviant containing predominantly gluconic acid produced by the genetically engineered (ΔpstS, P 112 :mgdh) Gluconobacter oxydans B58 through fermentation using non-recyclable paper as a growth substrate was used for the LIB leaching. At optimal bioleaching conditions of gluconic acid (160 mM), leaching time (2.5 h), reducing agent FeSO 4 to metal, i.e., cobalt (Co), nickel (Ni) and manganese (Mn), mole ratio (0.88), temperature (55 °C) and pulp density (2.5 %), the leaching efficiency was 87 % 72 %, 94 %, and 88 % for Co, Ni, Mn and lithium (Li), respectively. TEA analysis confirmed that bioleaching plant with an annual black mass processing capacity of 10,000 metric tons and plant life of 30 years would be economically viable with an NPV and profit margin of $136 million and 11 %, respectively. The predicted carbon footprint of gluconic acid-based bioleaching for recovering 1 kg of Co (13.2 kg of CO 2 eq.) is lower compared to that of most state-of-the-art leaching technologies. Moreover, gluconic acid-based bioleaching effectively recovered target metals when tested for different black mass chemistries.

Bioleaching↗
DOE OSTI2021

Influence of shrub willow buffers strategically integrated in an Illinois corn-soybean field on soil health and microbial community composition

We report soil serves many important ecological functions and is an integral part of our existence as a society. However, concerns for soil health are growing globally, in part due to the negative impacts of agricultural management on soil resources. The production of perennial bioenergy crops on marginal land in row-crop production systems is one solution that could improve land-use efficiency and address the sustainability of cropland management. Because the relationship between crop management and the environment is complex, more research is needed to evaluate the potential benefits perennial bioenergy crop production has on soil health, as well as other ecosystem services. In this study, shrub willow buffers were strategically integrated into a corn-soybean cropping system with the main objective of reducing nitrate-N leaching from grain crop production while producing biomass for bioenergy. Two buffer systems (defined by landscape positions) were included for comparison, one on marginal land with exposure to nitrate-N leaching from upslope grain (southern plots) and one on fertile soils with less nitrate-N leaching potential (northern plots). Evaluation of soil (chemistry, bulk density, microbial community) and shrub willow vegetation properties ( fine roots, leaf litter decomposition, and nutrient uptake dynamics), showed that landscape position plays an important role in (1) the dynamics of soil chemical properties, (2) shrub willow's influence and productivity, and (3) the provision of additional ecosystem services such as reductions in nitrous oxide emissions and nitrate-N leaching. In addition, the combination of crop type and landscape position (N-grain, N-willow, S-grain, and S-willow) influenced the species composition of the soil microbial community, resulting in unique and identifiable communities. These results highlight the potential application of shrub willow buffers for ecosystem service provision and support of ecosystem processes; however, understanding the relationship between the microbial community, crop type, and landscape is important for understanding the sustainability of the design.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Hanging String Cuts in SPR Caverns: Modeling Investigation and Comparison with Sonar Data

Investigation of leaching for oil sales includes looking closely at cavern geometries. Anomalous cavern "features" have been observed near the foot of some caverns subsequent to partial drawdowns. One potential mitigation approach to reducing further growth of preexisting features is based on the hypothesis that reducing the brine string length via a "string cue' would serve to move the zone associated with additional leaching to a location higher up in the cavern and thus away from the preexisting feature. Cutting of the hanging string is expected to provide a control of leaching depth that could be used to "smooth" existing features and thus reduce geomechanical instability in that region of the cavern. The SANSMIC code has been used to predict cavern geometry changes (i.e., the extent of cavern growth with depth) based on variable input parameters for four caverns: West Hackberry 11 (WH11), West Hackberry 113 (WH113), Big Hill 104 (BH104), Big Hill 114 (BH114). By comparing the initial sonar geometry with resultant geometries calculated by the SANSMIC code, conclusions may be drawn about the potential impact of these variables on future cavern growth. Ultimately, these conclusions can be used to assess possible mitigation strategies such as the potential advantage of cutting versus not cutting a brine string. This work has resulted in a recommendation that a hanging string cut of 80 ft in WH11 would be beneficial to future cavern geometry, while there would be little to no benefit to string cuts in the other three caverns investigated here. The WH11 recommendation was followed in 2019, resulting in an operational string cut. A sonar performed after the string cut showed no adverse leaching in the area of the preexisting flare, as expected from the results of the preliminary SANSMIC runs described in this report. Additional SANSMIC modeling of the actual amount of injected raw water resulted in good agreement with the post-cut sonar.

02 PETROLEUM↗
DOE OSTI2020

Characterization of Tank 11H samples from tank closure cesium removal (TCCR) Batch 3 - intermediate and final samples

Savannah River Remediation (SRR) is currently operating the Tank Closure Cesium Removal (TCCR) process to remove 137 Cs from tank waste supernate using an ion exchange process. The TCCR unit processes dissolved salt from Tank 10H through a series of ion exchange columns containing crystalline silicotitanate (CST) and the effluent is then discharged to Tank 11H. Four interim samples pulled from Tank 11H during and just after the completion of processing of Batch 3 through the TCCR process have been analyzed for 137 Cs activity and density. The 137 Cs activity was found to decrease with each subsequent sample, which is consistent with the addition of decontaminated solution to Tank 11H. When compared to the expected composition from mixing the Tank 10H Batch 3 feed with the material already present in Tank 11H, the bulk chemical composition was as expected. A corrosion control sample collected from Tank 11H in June 2020 showed changes in the chemical composition and 137 Cs activity when compared to the composition measured at the end of Batch 2 processing. As there were no additions made to the tank during this period, these changes were attributed to leaching of the solids present in Tank 11H. Revision 1 of this report contains additional analyses of the fourth interim sample including inductively coupled plasma – mass spectrometry (ICP-MS) results and activities of other radionuclides. These results are consistent with the previously reported results, showing leaching from the Tank 11H heel. Notably, the 90 Sr activity was about 2.7x higher than calculated from a mixture of the original Tank 11H supernate and the Tank 10H supernate as treated by TCCR, suggesting additional leaching of Sr from the Tank 11H heel solids. In addition, Revision 1 includes analysis results for the Batch 3 Post-Production surface and variable depth samples collected in October of 2020. The Post-Production surface sample was similar in composition to the fourth interim surface sample, except for the increased Cs-137 and oxalate concentrations that were presumably associated with leaching of the Tank 11H heel solids.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Characterization of Contaminants and Mobility in WMA A-AX Boreholes D0006 and D0008

This study was initiated to determine if subsurface contaminants in the A-AX vadose zone at the Hanford site (boreholes D0006 and D0008) caused corrosion of nearby stainless steel well casings (299-E-24-19, 299-E25-46, and 299-E25-236) and, based on the type and distribution of contaminants, determine if contaminants are from one or more sources including a) the A-104 and/or A-105 tanks, b) the 242A evaporator, and c) the 200-E-286 ditch. A tiered approach was used for characterizing contaminants in vadose zone sediments starting with mobile and total contaminant concentrations (Tier 1), characterizing contaminant speciation (Tier 2), and measuring contaminant leaching (Tier 3). Total and mobile contaminant measurements at seven depths showed elevated sulfate and nitrate in all samples (130 to 280 ft depth), elevated chloride in five depths, and no elevated radionuclides except I-129 in D0006 at 206 to 208 ft depth. If these contaminants were initially acidic, stainless-steel corrosion would occur. However, because sediments likely have a high acid neutralization capacity, an acidic spill would have been neutralized within tens of feet, so casing corrosion would likely occur in shallow sediments. GEL labs data also shows low (but above natural) chromate from shallow to 170 ft depth, then higher chromate to 280 ft, suggesting a surface Cr spill or casing corrosion. GEL labs data also showed evidence of more than one plume, with deep nitrate, sulfate, and chloride migration, but only shallow tritium migration. Tritium should migrate nearly unretarded in the subsurface like nitrate and chloride. Elevated aqueous cations and anions in the D0006 206 to 208' depth pore water (SO 4 2- , NO 3 - , Na + , K + , Ca 2+ , Mg 2+ , Si) could be the result of acid disposal and calcite dissolution at shallow depth, with deeper migration of SO 4 2- , NO 3 - from acids and Ca 2+ and Mg 2+ from calcite. Elevated Si (160 mg/L) indicates dissolution of clays or other silicates, which can also occur in acids. Acid extractable metals did show elevated Cr (but not Fe, Ni, Mo, and Mn) above natural levels, which may indicate stainless-steel well corrosion or transport of metals from a shallow spill. The elevated I-129 in D0006 at 206 to 208' depth was low with 0.34 μg/g in pore water and 1.5 μg/g total extractable I-129 in the sediment, which indicates significant fraction of I-129 was bound in one or more precipitates. Although total I-129 was below detection limits in most extractions due to high molybdate interference, I-127 analysis provided some insight into potential precipitate phases. Total I-127 was mainly extracted by acetate or acetic acid (67%), which may be iodine in calcite. Inorganic carbon measurement identified 1.65% calcite, and total organic carbon (TOC) was below detection limits, so iodine was not associated with organic matter. Nearly all the I-127 was present as iodide. In 1-D leach experiments, I-127 as iodide leached from the sediment within 2 pore volumes. Due to high and dynamic molybdate leaching from the sediment and interference with I-129 analysis, there were few quantifiable I-129 measurements. The calculated molybdate release rates from the sediment suggested Mo was being released from the same precipitate phase, such as molybdate incorporated into calcite. Overall, because there was little radioactive contamination measured in D0006 and D0008 boreholes, potential releases from A-104 and A-105 did not reach this location south of the A tank farm. Elevated cations and anions found in D0006 and D0008 at depth as the result of acidic disposal could cause shallow stainless steel casing corrosion. The nearby 242A evaporator generally contained alkaline waste and tritium, but the nearby 200-E-286 ditch generally contained high Cl - liquid effluent, so these are unlikely to be acidic sources.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Surface Modified Fly Ash for Value Added Products (SuMo Fly Ash)

The objective of this project is to develop a technology to encapsulate coal fly ash particles in sulfurized vegetable oil, enhancing physical and mechanical properties of the fly ash as a filler material when applied in commercial products. This project significantly advances the knowledge base and technology for synthesizing coated fly ash particles for application in different polymer matrices to increase cross-linking, compatibility, air-entrainment and to decrease the leaching potential of metals of concern. Specifically, the project focuses on (a) collection, and characterization of fly ash material from coal power plants; (b) development of Sulfurized Vegetable Oil (SVO) modified (SuMo) fly ash and their detailed characterization; (c) evaluation of the mechanical properties of the SuMo fly ash incorporated plastic and rubber composites for potential replacement of CaCO 3 or carbon black as filler materials with SuMo fly ash in plastic and rubber composites; (d) leaching potential of SuMo fly ash and SuMo fly ash-incorporated plastic and rubber composites to determine the rate of release of trace metals. The major findings of this project are: i) Sulfurized Vegetable Oil coated fly ash (SuMo fly ash) was successfully prepared with a particle size of ≤ 45 micron which exhibited hydrophobicity of contact angle > 90°; ii) the coating reduces leaching of metals (e.g., B, Cr) from fly ash when exposed to water; iii) incorporation of SuMo fly ash increases thermal stability and yield strength of plastics; iv) SuMo coating helps disperse fly ash particles into cured rubbers, natural rubber; (v) SuMo fly ash-incorporated plastic/cured rubbers compounds protects against leaching of toxic elements.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2025

FY24 Task 5: Leachate Disposition

Directly feeding sludge solids to the high-level waste (HLW) Waste Treatment Plant represents an alternative flowsheet seeking to initiate sludge processing as soon as possible. Key processing functions previously captured during baseline pretreatment operations include leaching and washing prior to solids concentration. These operations should be considered in the potential direct feed flowsheets to maximize waste feed loading, minimize HLW volume, and mitigate corrosion challenges associated with vitrification of high phosphate and fluoride concentrations. Additionally, single-shell tank (SST) retrievals and waste transfers to double-shell tanks (DSTs) in a direct feed flowsheet would likely also benefit from some level of leaching, washing, and solids concentration in order to reduce DST space and mission duration. These operations could occur in a new facility or potentially in available DSTs. If washing and leaching are utilized, an effective disposition pathway for the wash water and leachate solutions are needed. Three target species that benefit significantly from leaching and washing are phosphate, fluoride and aluminum. Phosphate (PO 4 3- ) and fluoride (F - ) can contribute substantially to the amount of carrier fluid needed for dissolution, and the resulting volume of liquid generated. Disposition of this retrieval solution should be evaluated in order to prevent crystallization of these anions throughout system processing. Since there is a high probability that any retrieval solutions will be at or near their PO 4 3- and F - solubility limits, evaporation or blending with a high Na supernate (>3.5 M) is not recommended for the wash water streams without a method to remove precipitants prior to solution disposal. Additionally, aluminum present in the southeast quadrant of the Hanford site represents roughly 60% of the waste solids in the initial processing tanks. These aluminum solids are in the form of gibbsite (Al(OH) 3 ) and can pose significant challenges for processing due to the fast-settling times and high solids loading associated with these materials. Easily remediated by caustic addition to the solids, these wash solutions could be processed through crystalline silicotitanate (CST) ion exchange columns to prepare the supernate solutions for disposition. The current target for feed conditions to the Low Activity Waste (LAW) melter are waste streams that contain nominally 5-6 M Na. Fractions within the tanks contain upwards of 0.2 M phosphate and fluoride in solution at 3.5 M Na. Concentrating these solutions above 5 M Na would result in an exceedance of the solubility limits, and potential for uncontrolled precipitation of the phosphate and fluoride crystal material. The resulting crystalline salt material is typically sodium fluoride phosphate, also referred to as natrophosphate (Na 7 FPO 4 ·19H 2 O). Salt phases are of importance in tank waste due to their chemical reactivity, which can result in precipitation, dissolution, or transformation, impacting any downstream processes (Bolling et al. 2020, Russell, Snow, and Peterson 2010). Salt generation and precipitation could pose challenges by causing system plugging and melter corrosion if left in the supernate stream, or limit sodium molarity of the supernate that would be accepted without incident in waste operations. To understand the impact of this salt generation, the crystallization of natrophosphate in multiple simulant feed matrices was studied to understand the implications of various tank waste supernate chemistries. Three matrices were examined: high PO 4 3- /low F - , low PO 4 3- /high F - , and an average matrix. Subsequent testing was performed with the average matrix with the inclusion of CsNO 3 , and a final run with the average matrix including CsNO 3 and a 137 Cs spike for tracer purposes.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Dispersible Colloid Facilitated Release of Organic Carbon From Two Contrasting Riparian Sediments

In aqueous systems, including groundwater, nano-colloids (1–100 nm diameter) and small colloids (<450 nm diameter) provide a vast store of surfaces to which organic carbon (OC) can sorb, precluding its normal bioavailability. Because nanomaterials are ubiquitous and abundant throughout Earth systems, it is reasonable that they would play a significant role in biogeochemical cycles. As such, mineral nano-colloids (MNC) and small colloids, formed through mineral weathering and precipitation processes, are both an unaccounted-for reservoir and unquantified vector for transport of OC and nutrients and contaminants within watersheds. Water extractions and leaching experiments were conducted under (1) aerobic (ambient) and (2) anaerobic (environmental chamber) conditions for each of two contrasting riparian sediments from (1) Columbia River, Washington and (2) Tims Branch, South Carolina. Water dispersible colloid-adsorbed OC was as high as 48% of OC for Tims Branch anaerobic batch water extraction and as low as 0% for Columbia River aerobic batch water extractions. Anaerobic leaching from column experiments yielded higher colloid and OC release rates. Transmission electron microscopy with electron dispersive spectroscopy mapping revealed organic carbon associated with aggregations of nano-particulate silicate minerals and Mossbauer identified nano-particulate goethite. This exploratory study demonstrates that mineral facilitated release of OC in riparian sediments is both significant and variable between locations.

Rod, Kenton A.↗
NASA NTRS1980

Cl, P2O5, U and Br associated with mineral separates from a low and a high Ti mare basalt

Low Ti basalt 12040 and high Ti basalt 75055 have approximately the same Cl/P2O5 ratio; the Cl is that remaining after a hot water leach. Pyroxene, plagioclase and ilmenite minerals separated from the basalts also tend to have this same Cl/P2O5 ratio. This is evidence that these major minerals do not control the ratio since Cl and P would not be expected to partition to the same extent into each mineral. Olivine appears to be a special case. It is proposed that the grains measured contained inclusions with leachable and P2O5-related Cl. Dilute acid leaches of whole rock and separated minerals have the same or nearly the same Cl/P2O5 ratios as the residual samples. Apatite and whitlockite were probably the phases leached. They must be constituents of the mesostasis and are present as microminerals or coatings on major mineral grains. The acid leach results imply little or no partition of Cl and P2O5 into major minerals.

Jovanovic, S.↗
NASA NTRS2001

Detection of Soluble and Fixed NH4+ in Clay Minerals by DTA and IR Reflectance Spectroscopy : A Potential Tool for Planetary Surface Exploration

Nitrogen is an essential element for life. It is the only element among the six major biogenic elements, C, O, S, O, P, H, whose presence in the Martian soil has not been positively and directly established. We describe here a study assessing the ability to detect NH4 in soils by two methods: differential thermal analysis (DTA) and infrared (IR) reflectance spectroscopy. Four standard clay minerals (kaolinite, montmorillonite, illite and attapulgite) and an altered tephra sample from Mauna Kea were treated with NH4 in this study. Samples of the NH4-treated and leached clays were analyzed by DTA and infrared (IR) reflectance spectroscopy to quantify the delectability of soluble and sorbed/fixed NH4. An exotherm at 270-280 C was clearly detected in the DTA curves of NH4-treated (non-leached) samples. This feature is assigned to the thermal decomposition reaction of NH4. Spectral bands observed at 1.56, 2.05, 2.12, 3.06, 3.3, 3.5, 5.7 and 7.0 microns in the reflectance spectra of NH4-treated and leached samples are assigned to the sorbed/fixed ammonium in the clays. The montmorillonite has shown the most intense absorbance due to fixed ammonium among the leached samples in this study, as a result of its high cation sorption capacity. It is concluded that the presence of sorbed or fixed NH4 in clays may be detected by infrared (IR) reflectance or emission spectroscopy. Distinction between soluble and sorbed NH4 may be achieved through the presence or absence of several spectral features assigned to the sorbed NH4 moietyi and, specifically, by use of the 4.2 micrometer feature assigned to solution NH4. Thermal analyses furnish supporting evidence of ammonia in our study through detection of N released at temperatures of 270-330 C. Based on these results it is estimated that IR spectra measured from a rover should be able to detect ammonia if present above 20 mg NH4/g sample in the surface layers. Orbital IR spectra and thermal analyses measured on a rover may be able to detect ammonia in soils as well but at higher abundances. The spectral features at 3.06 and 7.0 microns due to bound NH4 in clays and altered Hawaiian tephra appear to be the most promising for detection by orbital spectrometers. If N species are present on Mars the sedimentary deposits may be the best regions to look for them.

Janice, Bishop↗
NASA NTRS1996

Dissolution kinetics of a lunar glass simulant at 25 degrees C: the effect of pH and organic acids

The dissolution kinetics of a simulated lunar glass were examined at pH 3, 5, and 7. Additionally, the pH 7 experiments were conducted in the presence of citric and oxalic acid at concentrations of 2 and 20 mM. The organic acids were buffered at pH 7 to examine the effect of each molecule in their dissociated form. At pH 3, 5, and 7, the dissolution of the synthetic lunar glass was observed to proceed via a two-stage process. The first stage involved the parabolic release of Ca, Mg, Al, and Fe, and the linear release of Si. Dissolution was incongruent, creating a leached layer rich in Si and Ti which was verified by transmission electron microscopy (TEM). During the second stage the release of Ca, Mg, Al, and Fe was linear. A coupled diffusion/surface dissolution model was proposed for dissolution of the simulated lunar glass at pH 3, 5, and 7. During the first stage the initial release of mobile cations (i.e., Ca, Mg, Al, Fe) was limited by diffusion through the surface leached layer of the glass (parabolic release), while Si release was controlled by the hydrolysis of the Si-O-Al bonds at the glass surface (linear release). As dissolution continued, the mobile cations diffused from greater depths within the glass surface. A steady-state was then reached where the diffusion rate across the increased path lengths equalled the Si release rate from the surface. In the presence of the organic acids, the dissolution of the synthetic lunar glass proceeded by a one stage process. The release of Ca, Mg, Al, and Fe followed a parabolic relationship, while the release of Si was linear. The relative reactivity of the organic acids used in the experiments was citrate > oxalate. A thinner leached layer rich in Si/Ti, as compared to the pH experiments, was observed using TEM. Rate data suggest that the chemisorption of the organic anion to the surface silanol groups was responsible for enhanced dissolution in the presence of the organic acids. It is proposed that the increased rate of Si release is responsible for the one stage parabolic release of mobile cations and the relatively thin leached layer compared to experiments at pH 3 and 5.

NASA Discipline Life Support Systems↗
NASA NTRS2016

Influence of Measurement Uncertainties on Fractional Solubility of Iron in Mineral Aerosols over the Oceans

The atmospheric supply of mineral dust iron (Fe) plays a crucial role in the Earths biogeochemical cycle and is of specific importance as a micronutrient in the marine environment. Observations show several orders of magnitude variability in the fractional solubility of Fe in mineral dust aerosols, making it hard to assess the role of mineral dust for the global ocean biogeochemical Fe cycle. In this study we compare the operational solubility of mineral dust aerosol Fe associated with the flow-through leaching protocol to the results of the global 3-D chemical transport model GEOS-Chem. According to the protocol, aerosol Fe is defined as soluble by first deionized water leaching of mineral dust through a 0.45 m pore size membrane followed by acidification and storage of the leachate over a long period of time prior to analysis. To estimate the uncertainty in soluble Fe results introduced by the flow-through leaching protocol, we prescribe an average 50 (range of 30 to 70) fractional solubility to sub-0.45 m sized mineral dust particles that may inadvertently pass the filter and end up in the acidified (at pH1.7) leachate for a couple of month period. In the model, the fractional solubility of Fe is either explicitly calculated using a complex mineral aerosol Fe dissolution module, or prescribed to be 1 and 4. Calculations show that the fractional solubility of Fe derived through the flow-through leaching is higher compared to the model results. The largest differences (40) are predicted to occur farther away from the dust source regions, over the areas where sub-0.45 m sized mineral dust particles contribute a larger fraction of the total mineral dust mass. This study suggests that different methods used in soluble Fe measurements and inconsistences in the operational definition of filterable Fe in marine environment and soluble Fe in atmospheric aerosols are likely to contribute to the wide range of fractional solubility of aerosol Fe reported in the literature.

Soluble Iron↗
DOE OSTI2025

Extraction and Separation of Rare-Earth Elements from Coal Fly Ash and Leachate using a Recyclable Ionic Liquid

Coal fly ash (CFA) can be a promising source for recovering rare-earth elements (REEs), as it contains a broad range of REEs with average concentrations frequently exceeding those in traditional rare earth mines. Recent research from our group has demonstrated that REEs can be preferentially extracted from CFA solids using a recyclable ionic liquid (IL), betainium bis-(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]). When CFA was heated with the mixture of IL and an aqueous solution above 65°C, most leached REEs partitioned into the IL phase and were separated from the bulk elements. Subsequent acid stripping of the REE-loaded IL removed the REEs and regenerated the IL for reuse in multiple extraction cycles. This IL-based REE-CFA recovery method has been applied to ten CFA samples derived from different coal sources, including ash recovered from disposal ponds. Analysis of 34 elements confirmed the process consistently achieved high REE recovery efficiency, with strong selectivity over bulk and trace elements across diverse CFA types. In addition to the IL-solid extraction, the performance of [Hbet][Tf2N] in extracting REEs from fly-ash leachates have been evaluated by four commonly used leaching reagents, including HCl, HNO3, H2SO4, and citrate. During the IL-leachate extraction, [Hbet][Tf2N] was mixed and heated with a Class C fly ash leachate generated from each leaching reagent, followed by an acid stripping. It was observed that the partitioning and recovery of REEs increased as the leachate pH increased from 3 to 11. Among the investigated leachates, HCl and citrate proved to be the most compatible with IL extraction, exhibiting a slightly higher REE recovery and a lower non-REE co-extraction compared to the IL-solid extraction. Sc, Y, Nd, Sm, Gd, Dy, and Yb consistently showed a high recovery rate from both CFA solids and leachates. Notably, Pr, Tb, and Ho, which were not previously leached from the CFA solids, were partially recovered from the leachates. Overall, our studies revealed the strong potential of [Hbet][Tf2N] for effectively recovering REEs from leachates, highlighting its applicability as a sustainable strategy for other aqueous REE feedstocks. Furthermore, a techno-economic analysis will be performed to quantify the economic viability of the IL-based REE recovery method and guide future process improvement.

42 ENGINEERING↗
DOE OSTI2025

Field–scale evaluation of ecosystem service benefits of bioenergy switchgrass

Purpose-grown perennial herbaceous species are nonfood crops specifically cultivated for bioenergy production and have the potential to secure bioenergy feedstock resources while enhancing ecosystem services. This study assessed soil greenhouse gas emissions (CO 2 and N 2 O), nitrate (NO 3 -N) leaching reduction potential, evapotranspiration (ET), and water-use efficiency (WUE) of bioenergy switchgrass (Panicum virgatum L.) in comparison to corn (Zea mays L.). The study was conducted on field-scale plots in Urbana, IL, during the 2020–2022 growing seasons. Switchgrass was established in 2020 and urea-fertilized at 56 kg N ha –1 year –1 . Corn management followed best management practices for the US Midwest, including no-till and 202 kg N ha –1 year –1 fertilization, applied as urea–ammonium nitrate (32%). Our results showed lower direct N 2 O emissions in switchgrass compared to corn. Although soil CO 2 emissions did not differ significantly during the establishment year, emissions in subsequent years were over 50% higher in switchgrass than in corn, likely due to increased belowground biomass, which was over five times higher in switchgrass. Nitrate-N leaching decreased as the switchgrass stand matured, reaching 80% lower than in corn by the third year. Differences in ET and WUE between corn and switchgrass were not significant; however, results indicate a trend toward reduced WUE in switchgrass under drought, driven by lower aboveground biomass production. Our study demonstrates that switchgrass can be implemented at a commercial scale without negatively impacting the hydrological cycle, while potentially reducing N losses through nitrate-N leaching and soil N 2 O emissions, and enhancing belowground C storage.

09 BIOMASS FUELS↗
DOE OSTI2021

Effects of carbonation on the retention of heavy metals in chemically activated BOF slag pastes

Basic Oxygen Furnace slag contains heavy metals, including vanadium, chromium and molybdenum. The leachability of these elements determines the industrial applicability of slag-based building products. This study investigates the post‑carbonation leaching of heavy metals from activated BOF slag pastes with the focus on the activator dosage and type (sodium and potassium citrate). Results reveal that the high degree of brownmillerite hydration boosts the leachability of heavy metals as its hydration product- hydrogarnet is less stable upon carbonation. With two leaching procedures, it is demonstrated that the carbonation resistance of pastes becomes the main attribute in preventing the leaching of heavy metals. It can be enhanced by optimising the activator dosage to facilitate the hydration of C{sub 2}S and consequent structural densification.

36 MATERIALS SCIENCE↗
DOE OSTI2021

The effect of caustic soda treatment to recover rare earth elements from secondary feedstocks with low concentrations

Caustic soda (NaOH) treatment has enhanced rare earth element (REE) extraction from monazite. Here, this study examined the effectiveness of caustic soda for RE-phosphates with lower concentrations for extraction from coal overburden, an alternative feedstock derived from mining waste. Pourbaix (Eh-pH) diagrams were constructed for La, Ce, Nd, Eu, and Y-PO 4 -H 2 O systems to understand the thermodynamics of NaOH-facilitated acid leaching for low-concentration RE-phosphates and oxides and to elucidate the difference in recoveries among individual REEs. The Eh-pH diagrams indicated that low crystallinity is beneficial for extraction. Nd was thermodynamically most favorable for the extraction process among the five elements examined, and Y was the least promising. Experiments were conducted using three Pennsylvania coal overburden samples to validate the effect of caustic soda on rare earth leaching. The experimental results showed that for NaOH (6 M), a leaching time of 2 h at 125 °C was sufficient to obtain twice the recovery values compared to those without the NaOH treatment. After implementing the caustic soda treatment, a high total REE recovery (>60%), especially for Nd and Pr, could be achieved with diluted HCl and more environmentally friendlier citric acid. The results were similar for both coarse and fine particles. This novel approach is likely to improve the feasibility of REE extraction from coal-associated feedstock in a more environmentally benign manner.

42 ENGINEERING↗
DOE OSTI2021

Theoretical evidence that root penetration ability interacts with soil compaction regimes to affect nitrate capture

Abstract Background and Aims Although root penetration of strong soils has been intensively studied at the scale of individual root axes, interactions between soil physical properties and soil foraging by whole plants are less clear. Here we investigate how variation in the penetration ability of distinct root classes and bulk density profiles common to real-world soils interact to affect soil foraging strategies. Methods We utilize the functional–structural plant model ‘OpenSimRoot’ to simulate the growth of maize (Zea mays) root systems with variable penetration ability of axial and lateral roots in soils with (1) uniform bulk density, (2) plow pans and (3) increasing bulk density with depth. We also modify the availability and leaching of nitrate to uncover reciprocal interactions between these factors and the capture of mobile resources. Key Results Soils with plow pans and bulk density gradients affected overall size, distribution and carbon costs of the root system. Soils with high bulk density at depth impeded rooting depth and reduced leaching of nitrate, thereby improving the coincidence of nitrogen and root length. While increasing penetration ability of either axial or lateral root classes produced root systems of comparable net length, improved penetration of axial roots increased allocation of root length in deeper soil, thereby amplifying N acquisition and shoot biomass. Although enhanced penetration ability of both root classes was associated with greater root system carbon costs, the benefit to plant fitness from improved soil exploration and resource capture offset these. Conclusions While lateral roots comprise the bulk of root length, axial roots function as a scaffold determining the distribution of these laterals. In soils with high soil strength and leaching, root systems with enhanced penetration ability of axial roots have greater distribution of root length at depth, thereby improving capture of mobile resources.

59 BASIC BIOLOGICAL SCIENCES↗