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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

A Grand Canonical Monte Carlo simulation program for computing ion distributions around biomolecules in hard sphere solvents

The GIBS software program is a Grand Canonical Monte Carlo (GCMC) simulation program (written in C++) that can be used for 1) computing the excess chemical potential of ions and the mean activity coefficients of salts in homogeneous electrolyte solutions; and, 2) for computing the distribution of ions around fixed macromolecules such as, nucleic acids and proteins. The solvent can be represented as neutral hard spheres or as a dielectric continuum. The ions are represented as charged hard spheres that can interact via Coulomb, hard-sphere, or Lennard-Jones potentials. In addition to hard-sphere repulsions, the ions can also be made to interact with the solvent hard spheres via short-ranged attractive square-well potentials.

Source record↗
DOE OSTI2016

Lignin Valorization Via Laccase-Assisted Functionalization

With the diminishing supply of the world’s petroleum reserves and increasing environmental concerns, a heightened focus has been placed upon developing bio refineries to sustainably convert lignocellulosics to fuels, chemicals and materials. Furthermore, woody biomass represents a promising bio resource due to its abundance, renewability, and biodegradability. Lignin is an irregular polyphenolic macromolecule that typically constitutes ~15-35% of woody biomass. The pulp and paper industry produces lignin on the scale of millions of tons each year as a by-product of the pulping process. Traditionally, lignin has been viewed as a waste material that is combusted in the pulping process. But, in recent decades, there have been increased efforts devoted towards the conversion of lignin into value-added commodities, such as bio fuels, biomaterials, and bio-based chemicals. The valorization of lignin can be regarded as a necessary step for the development of lignocellulosic-based integrated bio refineries. Owing to the phenolic structure of lignin, it is possible to enzymatically graft molecules onto its surface using laccases (benzenediol: oxygen oxidoreductases, EC 1.10.3.2) to create exciting novel biomaterials. These environmentally friendly enzymes use oxygen as their only co-substrate and produce water as their sole by-product, and as a result have found compelling industrial applications. This mini-review highlights recent advances in the field of laccase-facilitated functionalization of lignin as well as promising future directions for lignin-based polymers.

09 BIOMASS FUELS↗
DOE OSTI2017

Contemporary Use of Anomalous Diffraction in Biomolecular Structure Analysis

The normal elastic X-ray scattering that depends only on electron density can be modulated by an ?anomalous? component due to resonance between X-rays and electronic orbitals. Anomalous scattering thereby precisely identifies atomic species, since orbitals distinguish atomic elements, which enables the multi- and single-wavelength anomalous diffraction (MAD and SAD) methods. SAD now predominates in de novo structure determination of biological macromolecules, and we focus here on the prevailing SAD method. We describe the anomalous phasing theory and the periodic table of phasing elements that are available for SAD experiments, differentiating between those readily accessible for at-resonance experiments and those that can be effective away from an edge. We describe procedures for present-day SAD phasing experiments and we discuss optimization of anomalous signals for challenging applications. We also describe methods for using anomalous signals as molecular markers for tracing and element identification. Emerging developments and perspectives are discussed in brief.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Biological Small Angle Scattering: Techniques, Strategies and Tips

This book provides a clear, comprehensible and up-to-date description of how Small Angle Scattering (SAS) can help structural biology researchers. SAS is an efficient technique that offers structural information on how biological macromolecules behave in solution. SAS provides distinct and complementary data for integrative structural biology approaches in combination with other widely used probes, such as X-ray crystallography, Nuclear magnetic resonance, Mass spectrometry and Cryo-electron Microscopy. The development of brilliant synchrotron small-angle X-ray scattering (SAXS) beam lines has increased the number of researchers interested in solution scattering. SAS is especially useful for studying conformational changes in proteins, highly flexible proteins, and intrinsically disordered proteins. Small-angle neutron scattering (SANS) with neutron contrast variation is ideally suited for studying multi-component assemblies as well as membrane proteins that are stabilized in surfactant micelles or vesicles. SAS is also used for studying dynamic processes of protein fibrillation in amyloid diseases, and pharmaceutical drug delivery. The combination with size-exclusion chromatography further increases the range of SAS applications.The book is written by leading experts in solution SAS methodologies. The principles and theoretical background of various SAS techniques are included, along with practical aspects that range from sample preparation to data presentation for publication. Topics covered include techniques for improving data quality and analysis, as well as different scientific applications of SAS. With abundant illustrations and practical tips, we hope the clear explanations of the principles and the reviews on the latest progresses will serve as a guide through all aspects of biological solution SAS.The scope of this book is particularly relevant for structural biology researchers who are new to SAS. Advanced users of the technique will find it helpful for exploring the diversity of solution SAS methods and applications.

Chaudhuri, Barnali↗
DOE OSTI2018

Coated substrate apparatus and method

A coated substrate is formed with aligned objects such as small molecules, macromolecules and nanoscale particulates, such as inorganic, organic or inorganic/organic hybrid materials. In accordance with one or more embodiments, an apparatus or method involves an applicator having at least one surface patterned with protruded or indented features, and a coated substrate including a solution-based layer of objects having features and morphology attributes arranged as a function of the protruded or indented features.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Multiphase Reacting Flow Simulations and Optimization of Commercial-Scale Aerobic Bioreactors

Aerobic bioreactors are widely used in the synthesis of value-added products in pharmaceutical and biotechnology industries, wherein microbial bioreactions aid in the conversion of sugars to macromolecules. These reactors are also being actively investigated as a cost-effective pathway for the production of low-value commodities such as biofuels and animal feed. Reactor scale-up is one of the important challenges when designing these systems. Gas and liquid phase transport, mass-transfer, and mixing physics at large length scales can significantly affect microbial conversion rates, particularly when the microbial reaction requires a narrow set of conditions. These phenomena are difficult to study in small-scale bench-top reactors that are typically well-mixed. Predictive computational fluid dynamics (CFD) based simulations can therefore aid in the design and optimization of these reactors. This work presents multiphase Euler-Euler CFD simulations of commercial-scale (~ 500 m3) aerobic bioreactors. Our mathematical model treats the gas and liquid as interpenetrating phases. This approach reduces the computational complexity of tracking individual gas bubbles that are several orders of magnitude smaller than reactor dimensions. We solve the Reynolds averaged Navier-Stokes (RANS) multiphase equations that account for phase and chemical species transport, interphase mass and momentum transfer and uses a phenomenological model for oxygen uptake by microbes. We use a customized solver derived from open-source CFD toolbox, OpenFOAM, to perform these simulations, which has been validated against small-scale reactors in our previous work. This work examines the performance of three different reactor designs, viz. bubble column reactor, airlift reactor with an internal draft tube, and a stirred-tank reactor with Rushton impellers. Reactor oxygen mass-transfer coefficient, gas hold-up, and oxygen distribution are critically analyzed among reactors, and sensitivity studies pertaining to gas flow rates and reactor geometry will be presented.

09 BIOMASS FUELS↗
DOE OSTI2019

Roundtable on Chemical Upcycling of Polymers (Brochure)

Plastics are ubiquitous in modern life. They are made from synthetic carbon-based polymers—organic macromolecules made up of many repeating subunits called monomers—and are designed to be durable and resistant to degradation. Global plastics production has reached a rate of over 400 million metric tons per year, with over 8 billion metric tons produced in the past 50 years. Average production has increased by 36% in the past decade and is projected to grow to 700 million metric tons in 2030—about 80 kg of plastics produced for every human on earth. Globally, 20% of discarded plastics are recycled (<10% in the United States), primarily using mechanical processes, and about 25% are incinerated for energy recovery. More than half are deposited into landfills or released into the environment. Thus, plastic waste poses a long-term environmental challenge: e.g., at the current rate of plastics production and disposal, the mass of plastic waste in the ocean is predicted to exceed the mass of fish by 2050.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Coupled Microbial-Conversion and Computational-Fluid-Dynamics (CFD) Models for Butanediol Production in Micro-Aerated Reactors

Microbial conversion of substrates to macromolecules has been widely used in the synthesis of value-added products in pharmaceutical and biotechnology industries. These bioreactions are also being investigated in the production of low-value commodities such as biofuels [1]. Gas-liquid mass-transfer and transport-reaction coupling are important challenges when designing and scaling up these reactor systems. Experiments in wellmixed small-scale reactors have enabled characterization of microbial reactivity, while their coupling with macroscale transport remains relatively unexplored. In this work, we use a coupled metabolic-CFD model to study the action of a genetically engineered microbe Zymomonas mobilis [2] on sugars to produce 2,3-Butanediol (BDO). BDO is an important hydrocarbon intermediate that can be catalytically upgraded to several fuels and chemicals [3]. An important aspect to this particular microbial conversion is the need for micro-aerated environments as opposed to traditional aerobic fermentation. Slight variations in oxygen concentration can result in competing reaction pathways that disable BDO production. Hence, gas-liquid mass transfer and transport need to be optimized in large-scale reactors to maximize BDO production, for which CFD is a valuable tool. The aerobic-fermentation CFD model previously developed by the authors [5] for simulating bubble-column and airlift reactors at scale was used in this study. The Reynolds-averaged mass, momentum and energy transport equations for interpenetrating gas and liquid phase are solved in this model along with the transport and interphase mass transfer of oxygen. Our previous work used a phenomenological model for microbial oxygen uptake that neglected microbial growth and other reaction pathways. In this work, a detailed metabolic model enabled prediction of product formation and inhibition pathways. In order to manage computational cost, we used a subcycling technique [6] that takes advantage of the clear separation in transport (~ 200 sec) and reaction (~ 2-3 hours) timescales. The CFD model is first solved to steady state, after which the metabolic model is advanced at every cell in the computational domain using the local oxygen concentration. The CFD model is then run to achieve a new steady state that provides a new oxygen distribution for the metabolic model. This process, where reaction and fluid updates are interleaved together, is iterated until reactants are completely exhausted. This work will examine the performance of different reactor designs such as bubble column and airlift reactors at scale (250-500 m3). Oxygen mass-transfer coefficient and distribution are critically analyzed among reactors, and optimization studies pertaining to aeration is presented. Furthermore, it has been observed in experiments that high BDO production may be achieved by manipulating the aerobic environment over the course of reaction, such that oxygen concentration is high during the growth phase, and very low as sugar is depleted. This characteristic will be addressed by our simulations for which a timedependent scheduling strategy for aeration is presented that maximizes BDO production. [1] Humbird, D., Davis, R., and McMillan, J., Aeration costs in stirred-tank and bubble column bioreactors, Biochemical Engineering Journal, 127, 161—166, 2017 [2] Yang, S., Mohagheghi, A., Franden, M. A., Chou, Y.-C., Chen, X., Dowe, N., Himmel, M. E., and Zhang, M., Metabolic engineering of zymomonas mobilis for 2, 3-butanediol production from lignocellulosic biomass sugars. Biotechnology for biofuels, 9(1):189, 2016 [3] Kim, S. J., Sim, H. J., Kim, J. W., Lee, Y. G., Park, Y. C., and Seo, J. H., Enhanced production of 2,3-butanediol from xylose by combinatorial engineering of xylose metabolic pathway and cofactor regeneration in pyruvate decarboxylase-deficient Saccharomyces cerevisiae. Bioresource Technology, 245:1551–1557, 2017 [4] Weller, H., Tabor, G., Jasak, H. and Fureby, C., A tensorial approach to computational continuum mechanics using object-oriented techniques, Computers in physics, 12, 6, 620--631, 1998

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2022

Study on Emulsification/Demulsification Behavior and Mechanism of Produced Liquid from Polymer Flooding on Alaska North Slope

Heavy oil reservoirs on Alaska North Slope (ANS) are unconsolidated and contain abundant clay minerals, where the first-ever field pilot is currently implemented to validate the use of polymer floods for heavy oil enhanced oil recovery (EOR). The polymer molecules and/or fine clay particles carried with the produced liquid could potentially affect the oil/water separation, which is one of the major concerns for field operators. This dissertation aims to investigate the emulsification behavior of produced liquid, understand the emulsifying mechanism, and seek an adaptive and cost-effective method to treat the produced liquid from polymer flooding. Emulsions were prepared by mechanically mixing the actual heavy oil and the produced water from the pilot site, of which the stability was investigated by bottle test method or multiple light scattering method. Drop size distribution and interfacial properties were measured via microscope and pendant drop technique to probe the stability mechanism further. Results showed that oil-continuous or water-continuous emulsion could be generated depending on the water cut, clay types, clay concentration, and polymer concentration. In the crude oil/water system, the increasing water cut triggered the phase inversion of oil-continuous emulsion to water-continuous emulsion, resulting in faster separation and lower emulsion stability. Whereas, clay particles, no matter added to the oil or water phase, resulted in an unfavorable phase inversion from the loose water-continuous emulsion to the tight oil-continuous emulsion as clay concentration increased. For all four types of clay except Ca-montmorillonite, clay particles added to water led to an earlier phase inversion and higher emulsion stability than that added to the oil. The dual function of polymer on emulsion stability was observed. On the one hand, both sheared and unsheared polymer tended to convert the oil-continuous emulsion formed in either crude oil/water system or complex crude oil/water/clay particle system to the water-continuous emulsion, acting as a weak demulsifier to accelerate the oil/water separation. On the other hand, the addition of polymer to the water-continuous emulsion could result in enhanced emulsion stability, which is primarily attributed to the increased viscosity of the continuous phase and the decreased drop size of the dispersed oil phase. Particularly, the sheared polymer had a weaker ability to stabilize the o/w emulsion than the unsheared polymer due to the lower viscosity of the sheared polymer solution resulting from the breakdown of the polymer macromolecules. As for the chemical demulsification tests, the performance of demulsifiers showed a complex dependency upon the water cut, the shearing intensity, demulsifier type and dosage, and the polymer concentration. A compound emulsion breaker, E12+E18, exhibited the most satisfactory demulsification performance despite the varied test conditions. For severe water-continuous emulsions that might require a multi-fold dosage of demulsifier, a less expensive electrolyte, KCl, was proposed to be used in combination with demulsifier E12+E18 to improve the demulsification performance. In the proposed demulsifier formula, the effectiveness of the commercial demulsifier relied on its destructive effect on the interfacial film, while the efficacy of KCl was mainly dependent on its viscosity reduction effect on the continuous phase. This dissertation illustrates that intermediate layer elimination and water clarification are the major challenges for produced liquid treatment from polymer flooding. It also provides practical and theoretical guidance in advance for the demulsification strategy of the produced liquid from the ongoing first-ever polymer flooding pilot on ANS.

Chang, Hongli↗
DOE OSTI2016

Synergetic Interactions between Uranium, Humic Acid, Silica Colloids and SRS Sediments at Variable pH - 16524

The Savannah River Site (SRS) was constructed during the 1950's and became one of the major producers of plutonium for the United States during the Cold War. During its production life, the F/H Area Seepage Basins received approximately 1.8 billion gallons of acidic waste containing radionuclides and dissolved heavy metals. This led to the creation of a highly contaminated groundwater plume with uranium (VI) as a key contaminant of concern within the plume. Now, as a designated hazardous waste management facility, the main activities taking place at the site are nuclear storage and remediation of contaminated soil and groundwater from radionuclides. Humic substances (HS) are major components of soil organic matter having the ability to influence migration behavior and fate of heavy metals and are being investigated for potential use in environmental remediation at SRS. Essentially, HS are polyfunctional organic macromolecules formed by the chemo-microbiological decomposition of biomass or dead organic matter. HS are able to interact with both metal ions and organic compounds based on solubility. Humic acid (HA) represents the fraction of HS soluble at pH greater than 3.5. HA carries a large number of functional groups, provides an important function in ion exchange and is a metal complexing ligand with a high complexation capacity. Silica is the term applied to solid forms with the stoichiometric composition of SiO{sub 2}. The colloidal silica used in this work is amorphous and non-porous in suspension; silica's net surface charge for pH values higher than 3 is negative, due to the isoelectric point being 1.5 - 2.5. Humic acid has been previously used in remediation techniques and silica is found naturally in the soil. This investigation studied the synergistic interactions between four key components: U(VI), humic acid (HA), colloidal silica and SRS sediment under varying pH conditions ranging from 3 to 8. Multi-component batch systems were constructed to effectively analyze the removal of U(VI). The batches were pH adjusted, left to equilibrate for a minimum of 48 hours on a shaker, and then centrifuged. A set of samples, filtered to remove any colloids in suspension, and a set of unfiltered samples were analyzed. For the samples at acidic pH, the uranyl cation is the dominant species; with increasing pH, the mononuclear and polynuclear hydrolyzed uranyl ions become dominant based on speciation modeling. In filtered samples, uranium removal is highest at low pH with the negatively charged moieties of HA readily binding to the uranyl cation. Percent removal of U(VI) steadily decreased with an increase in pH and then remained comparable at a neutral/alkaline pH with the change in uranyl speciation. The percentage of colloidal silica removal was observed to be approximately 80% for both sediment- and non-sediment-bearing samples. As the pH increased, the silica removal in the non-sediment set showed a slight decrease and was in the range of 70% - 75%. Uranium removal in the unfiltered samples showed similar trends as compared to the filtered samples; however, the removal of uranium in the unfiltered samples was slightly lower compared to the filtered samples. Colloidal silica removal in non-sediment-bearing batches showed a decline with increasing pH, from 90% to 50%; conversely, the silica removal remained constant for the sediment-bearing batches at approximately 60%. Colloidal silica does not seem to have a significant effect on the removal of U(VI) before filtration due to U(VI) bound to colloidal silica remaining in suspension. The presence of humic acid, silica colloids, and SRS sediment was shown to synergistically effect the removal of U(VI). (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Study of Synergetic Interactions between Uranium, Humic Acid, Silica Colloids and SRS Sediments - 18581

The Savannah River Site's (SRS) F/H Area Seepage Basins received approximately 1.8 billion gallons of acidic waste containing radionuclides and dissolved heavy metals. This led to the creation of a highly contaminated groundwater plume with uranium (VI) as a key contaminant of concern within the plume. Humic substances (HS) are major components of soil organic matter having the ability to influence migration behavior and fate of heavy metals and are being investigated for potential use in environmental remediation at SRS. HS are polyfunctional, organic macromolecules able to carry a large number of functional groups which is an important function in ion exchange and is a metal complexing ligand with a high complexation capacity. Humic acid (HA) represents the fraction of HS soluble at pH greater than 3.5. Silica, naturally found in soil, is the term applied to solid forms with the stoichiometric composition of SiO{sub 2}. The colloidal silica used in this work is amorphous and non-porous in suspension. This investigation studied the synergistic interactions between four key components: U (VI), humic acid (HA), colloidal silica and SRS sediment; the interactions were studied under pH 3 - 8. Multi-component batch systems were constructed to effectively analyze the U (VI) removal. The results show that filtered and unfiltered samples depicted similar trends; while, filtered samples had more overall removal than the unfiltered samples at the varying pH levels. Colloidal silica does not have a significant effect on the removal of U (VI) due to U (VI) bound to colloidal silica remaining in suspension. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Effect of Minerals on the Removal of Uranium (VI) in the Presence of Humic Acid and Colloidal Silica - 19406

Uranium is one of the key contaminants of concern in groundwater as a result of past nuclear processing activities at the Department of Energy (DOE) facilities such as the Savannah River Site (SRS) in Aiken, South Carolina. SRS was one of the major nuclear processing facilities during the Cold War where plutonium was produced. Beginning with the implementation of the environmental cleanup program in 1981, SRS has become a hazardous waste management facility responsible for the storage and remediation of contaminated soil and groundwater from radionuclides. Approximately 1.8 billion gallons of acidic waste containing radionuclides and dissolved heavy metals was disposed in the F/H Area seepage basins. This led to the unintentional creation of highly contaminated groundwater plumes, consisting of radionuclides with an acidic pH between 3 and 5.5. The acidity of the plumes contributed to the mobility of several constituents of concern (COC) such as tritium ({sup 3}H), uranium-238 ({sup 238}U), iodine-129 ({sup 129}I), and strontium-90 ({sup 90}Sr) for the F-Area plume and {sup 3}H, {sup 90}Sr and mercury for the H-Area plume. This investigation will focus on uranium in the oxidation state +6 (U(VI)), which is a key contaminant of concern in the groundwater plume of the FArea. Initially, the pump-treat-reinject system was implemented from 1997 to 2003 to remove contaminants from polluted groundwater. Downgrade groundwater within the system would be pumped to the water treatment facility and re-injected upgrade within the aquifer. The effectiveness and sustainability of this process diminished over time. Therefore, it was discontinued and replaced with a funnel-and-gate process in 2004. This new process injects sodium hydroxide directly into the gates of the F-Area groundwater to effectively raise pH levels. By raising the pH of the groundwater, a treatment zone is created by reversing the acidic nature of the contaminated sediments and producing a negative net charge on the surface of sediment particles. As a result, the adsorption of cationic contaminants is expected to be enhanced. So far, this process has resulted in a decrease of {sup 90}Sr and {sup 238}U concentrations, though the concentration of iodine has been unaffected by this treatment. The solution used for the injections contains a high carbonate alkalinity in order to overcome the surface acidic conditions and natural partitions in the groundwater system. To maintain the neutral pH in the treatment zone, systematic injections are required. The continuous use of high concentrations of a carbonate solution to raise pH could re-mobilize uranium previously adsorbed within the treatment zone, though this has not been observed in the monitoring data. Humic substances (HS) are major components of soil organic matter. HS are polyfunctional organic macromolecules formed by the chemo-microbiological decomposition of biomass or dead organic matter. These substances are usually divided into three main fractions: humin (insoluble at all pH values), humic acid (soluble at pH greater than 3.5), and fulvic acid (soluble at all pH values). Humic acid carries a large number of functional groups such as aromatic rings, carboxyl groups, phenols, aliphatic chains, etc. Humic acid is an important ion exchange and metal complexing ligand with a high complexation capacity. The ability of humic acid to chemically bind to metals influences in their migration behavior and fate in natural systems. Various studies have suggested that the retention of U(VI) via sorption in the presence of humic acid is a complex process. For instance, humic acid can form an organic coating at the surface of minerals, which can enhance the sequestration of metals. Ivanov et al. (2012) studied the sorption of U(VI) sorption onto bentonite in the presence and absence of humic acid. The study found that uranium sorption in the presence of humic acid was enhanced at low pH (below 3.8) while at moderate pH (3.8 and 6.5) uranium sorption was reduced compared to the absence of humic acid. At high pH (7 and 9), uranium sorption was reduced for both the presence and absence of humic acid. Also, Krepelova et al. (2007) not only found that U(VI) sorption onto kaolinite was influenced by pH, U(VI) concentration, the presence of inorganic carbon species, and humic acid but also that U(VI) preferred to be adsorbed onto kaolinite as a uranyl-humate complex. This investigation analyzed the mechanisms of the synergetic interactions of humic acid and colloidal silica on the removal of uranium in the presence of pure minerals such as quartz, kaolinite and goethite which are characteristic of the F/H area. (authors)

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

Study of an Unrefined Humate Solution as a Possible Attenuation-based Remedy for Uranium Contamination in Acidic Groundwater - 20351

The Savannah River Site (SRS), joined the environmental cleanup program in 1981 after the Cold War, and was designated as a hazardous waste management facility. About 1.8 billion gallons of acid wastes were disposed into the F/H Area Seepage Basin that included many radionuclides and dissolved metals, resulting in highly contaminated groundwater plumes with pH of 3 - 5.5. The acidity of the plumes contributes to the mobility of several constituents of concern (COC) such as H-3, U-238, I-129, and Sr-90 for the F-Area plume and H-3, Sr-90 and mercury for the H-Area plume. An active treatment (pump-and-treat and re-injection) system was constructed and put in place in 1997 to address the removal of metals and radionuclides from the contaminated groundwater. As remediation projects advanced, active treatments were transitioned to more passive or enhanced-passive approaches such as the subsurface barrier with base injection system, which has been controlling the mobility of contaminants. However, new and more efficient attenuation-based remedies are always sought. Several studies have proposed that humic substances can be used to remediate sites contaminated with heavy metals by creating a permeable reactive barrier. Humic substances (HS) are major components of soil organic matter. HS are polyfunctional organic macromolecules formed by the chemo-microbiological decomposition of biomass or dead organic matter. These substances are usually divided into three main fractions: humin (insoluble at all pH values), humic acid (soluble at pH greater than 3.5), and fulvic acid (soluble at all pH values). Humic substances are major components of the soil at SRS and, in addition, are also helpful in the removal process of uranium. This research focuses on uranium (VI), which is a key contaminant of concern in the F-Area groundwater plume. The interaction of uranium with sediment in the presence or absence of humic substances involves complex mechanisms that are not yet well understood. The interaction of U(VI) with humic substances can affect the adsorption of U on sediment, altering its mobility in the subsurface. The objective of this study is to study the mobility of uranium in the presence of humic acid and to determine if sediments amended by humic acid can enhance the sorption of heavy metals onto sediments. In this research, experiments were conducted using background (clean) F-Area aquifer sediments to understand and predict uranium mobility. A blended material, humate, containing both humic and fulvic acids and a chemically modified humate (KW15 modified humic or mod-HA) was studied as a possible amendment for uranium remediation in SRS groundwater. Batch experiments were conducted in triplicates using 20 ml of aqueous suspension in DI water containing SRS sediment and mod-HA and studied the effect of pH, kinetics of humate sorption onto SRS sediment and also studied the sorption of uranium onto mod-HA amended SRS sediment. Results indicate that mod-HA amended sediment increases uranium removal significantly. (authors)

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

Large-scale atomistic model construction of subbituminous and bituminous coals for solvent extraction simulations with reactive molecular dynamics

Large-scale atomistic models for complex polycyclic aromatic hydrocarbon systems help understand the chemical properties and behaviors of complex feedstocks such as coal or petroleum. However, the development and utilization of large-scale models remain limited due to the difficulty in achieving the varied structural characteristics necessary to capture stochastic nature of these feedstocks. Here we demonstrate a systematic workflow to construct stochastic molecular systems from a broad analytical suite: high-resolution transmission electron microscopy (HRTEM), carbon-13 nuclear magnetic resonance spectroscopy ( 13 C NMR), laser desorption ionization mass spectroscopy (LDI-MS), and elemental analysis. We present a model construction and analysis utility of a new Python-based module. We selected one subbituminous and three high-volatile bituminous coals to construct large-scale models (~40,000 atoms). The constructed models were utilized to examine the affinity for solvent extraction (naphthalene or tetralin) and the effect of structural properties (e.g., aromatic cluster size, functional groups, and cross-linking) in reactive molecular dynamics simulations. Complex chemical reactions were monitored with bond order transitions, intermediates formation, and mass distributions. Reactive molecular dynamics simulations suggest a plausible chemical extraction process and products for the complex fossil feedstocks. The results indicated that radical formations with bond breaking of bridging oxygens and carbons were required at high temperatures to facilitate hydrogeneration and extraction of gas molecules from radical-free molecules. We observed that aliphatic chains of tetralin were easily decomposed and combined with radicals to form small size of molecules with aryl bonding, mainly increasing molecules in the 500–1000 Da, while naphthalene had little impact on chemical extraction process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗