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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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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Activation and Assembly of Plasmonic-Magnetic Nanosurfactants for Encapsulation and Triggered Release

Multifunctional surfactants hold great potentials in catalysis, separation, and biomedicine. Highly active plasmonic-magnetic nanosurfactants are developed through a novel acid activation treatment of Au–Fe 3 O 4 dumbbell nanocrystals. The activation step significantly boosts nanosurfactant surface energy and enables the strong adsorption at interfaces, which reduces the interfacial energy one order of magnitude. Mediated through the adsorption at the emulsion interfaces, the nanosurfactants are further constructed into free-standing hierarchical structures, including capsules, inverse capsules, and two-dimensional sheets. The nanosurfactant orientation and assembly structures follow the same packing parameter principles of surfactant molecules. Furthermore, nanosurfactants demonstrate the capability to disperse and encapsulate homogeneous nanoparticles and small molecules without adding any molecular surfactants. The assembled structures are responsive to external magnetic field, and triggered release is achieved using an infrared laser by taking advantage of the enhanced surface plasmon resonance of nanosurfactant assemblies. Finally, solvent and pH changes are also utilized to achieve the cargo release.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Quantum dynamical effects of vibrational strong coupling in chemical reactivity

Abstract Recent experiments suggest that ground state chemical reactivity can be modified when placing molecular systems inside infrared cavities where molecular vibrations are strongly coupled to electromagnetic radiation. This phenomenon lacks a firm theoretical explanation. Here, we employ an exact quantum dynamics approach to investigate a model of cavity-modified chemical reactions in the condensed phase. The model contains the coupling of the reaction coordinate to a generic solvent, cavity coupling to either the reaction coordinate or a non-reactive mode, and the coupling of the cavity to lossy modes. Thus, many of the most important features needed for realistic modeling of the cavity modification of chemical reactions are included. We find that when a molecule is coupled to an optical cavity it is essential to treat the problem quantum mechanically to obtain a quantitative account of alterations to reactivity. We find sizable and sharp changes in the rate constant that are associated with quantum mechanical state splittings and resonances. The features that emerge from our simulations are closer to those observed in experiments than are previous calculations, even for realistically small values of coupling and cavity loss. This work highlights the importance of a fully quantum treatment of vibrational polariton chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Improved Treatment of 1–4 Interactions in Force Fields for Molecular Dynamics Simulations

Traditional force fields commonly use a combination of bonded torsional terms and empirically scaled nonbonded interactions to capture 1-4 energies and forces of atoms separated by three bonds in a molecule. While this approach can yield accurate torsional energy barriers, it often leads to inaccurate forces and erroneous geometries and creates an interdependence between dihedral terms and nonbonded interactions, complicating parametrization and reducing transferability. Here, in this paper, we demonstrate that 1-4 interactions can be accurately modeled using only bonded coupling terms, eliminating the need for arbitrarily scaled nonbonded interactions altogether. Furthermore, by leveraging the automated parametrization capabilities of the Q-Force toolkit, we efficiently determine the necessary coupling terms without the need for manual adjustment. Our approach is first validated on a range of small molecule systems, encompassing both flexible and rigid structures, and shows a significant improvement in force field accuracy, obtaining subkcal/mol mean absolute error for every molecule tested. We further extend the bonded-only model for 1-4 interactions to Amber ff14sb, CHARMM36, and OPLS-AA force fields to reproduce ab initio gas and implicit solvent ϕ,ψ surfaces of alanine dipeptide.

Abdullah, Aalim S. [University of California, Berk↗
DOE OSTI2020

Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines

8-Hydroxyquinolines (8HQs) are a family of lipophilic metal ion chelators that have been used in a range of analytical and pharmaceutical applications over the last 100 years. More recently, CQ (clioquinol; 5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) have undergone clinical trials for the treatment of Alzheimer’s disease and Huntington’s disease. Because CQ and PBT2 appear to redistribute metals into cells, these compounds have been redefined as copper and zinc ionophores. Despite the attention surrounding the clinical trials and the clear link between 8HQs and metals, the fundamental solution chemistry of how these compounds bind divalent metals such as copper and zinc, as well as their mechanism(s) of action in mammalian systems, remains poorly understood. Here, we used a combination of X-ray absorption spectroscopy (XAS), high-energy resolution fluorescence detected (HERFD) XAS, electron paramagnetic resonance (EPR), and UV–visible absorption spectroscopies to investigate the aqueous solution chemistry of a range of 8HQ derivatives. To circumvent the known solubility issues with 8HQ compounds and their complexes with Cu(II), and to avoid the use of abiological organic solvents, we have devised a surfactant buffer system to investigate these Cu(II) complexes in aqueous solution. Our study comprises the first comprehensive investigation of the Cu(II) complexes formed with many 8HQs of interest in aqueous solution, and it provides the first structural information on some of these complexes. We find that halogen substitutions in 8HQ derivatives appear to have little effect on the Cu(II) coordination environment; 5,7-dihalogenated 8HQ conformers all have a pseudo square planar Cu(II) bound by two quinolin-8-olate anions, in agreement with previous studies. Conversely, substituents in the 2-position of the 8HQ moiety appear to cause significant distortions from the typical square-planar-like coordination of most Cu(II)-bis-8HQ complexes, such that the 8HQ moieties in the Cu(II)-bis-8HQ complex are rotated approximately 30–40° apart in a “propeller-like” arrangement.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Use of Renewable Alcohols in Autocatalytic Production of Aspen Organosolv Lignins

This study aimed to investigate the intrinsic efficiency of renewable alcohols, applied under autocatalytic conditions, for removing lignin from aspen and hot-water-extracted aspen while substantially preserving the lignin structure so as to facilitate various valorization strategies. Ethylene glycol (EG), propylene glycol (PG), 1,4-butanediol (BDO), ethanol (EtOH), and tetrahydrofurfuryl alcohol (THFA) were evaluated based on their lignin solubilization ability, expressed as the relative energy difference (RED) following the principles of the Hansen solubility theory. The findings indicate that alcohols with a higher lignin solubilization potential lead to increased delignification, almost 90%, and produce a lignin with a higher content of β-O-4 bonds, up to 68% of those found in aspen milled wood lignin, thereby indicating their potential for valorization through depolymerization. However, these alcohols also produce lignin with a higher content of β-β and β-5 bonds, resulting in a higher molecular weight and polydispersity, due to readily occurring homolytic reactions. Hot-water extraction (HWE) conducted prior to alcohol treatment reduced the delignification efficiency and resulted in a lignin with a lower β-O-4 bond content. The lignins produced in these experiments exhibited a superior UV-A absorption capacity compared with synthetic benzophenone, as well as a greater radical quenching ability than synthetic butylated hydroxytoluene, indicating their potential for use in the protection of polymers against degradation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Reliable p K a Prediction through Efficient Incorporation of Anharmonicity within the Nuclear–Electronic Orbital Framework

Accurate pK a prediction is critical for understanding chemical reactivity and molecular properties across a wide range of applications. Computational approaches usually invoke a harmonic treatment of the vibrational modes for zero-point energies, as well as thermal and entropic contributions. Herein, we present a general protocol for relative pK a prediction that incorporates the significant anharmonic effects using nuclear–electronic orbital (NEO) theory. This protocol is validated against experimental data for a range of molecules in acetonitrile, including protonated nitrogen bases, nitrophenols, anilines, and diamines, as well as cobalt electrocatalysts. For simple acids, the NEO approach offers only a slight improvement over conventional density functional theory with the standard harmonic vibrational treatment, whereas for hydrogen-bonded acids, the NEO approach offers more significantly improved performance at a comparable computational cost. This accessible methodology provides a practical route for accurate pKa prediction in challenging systems and is extendable to related thermodynamic properties such as hydricities and proton-coupled redox potentials.

Density functional theory↗
DOE OSTI2025

Modeling the Behavior of Complex Aqueous Electrolytes Using Machine Learning Interatomic Potentials: The Case of Sodium Sulfate

Understanding the structure and thermodynamics of solvated ions is essential for advancing applications in electrochemistry, water treatment, and energy storage. While ab initio molecular dynamics methods are highly accurate, they are limited by short accessible time and length scales whereas classical force fields struggle with accuracy. Herein, we explore the structure and thermodynamics of complex monovalent-divalent ion pairs using Na 2 SO 4 (aq) as a case study by applying a machine learning interatomic potential (MLIP) trained on density functional theory (DFT) data. Our MLIP-based approach reproduces key bulk properties such as density and radial distribution functions of water. We provide the hydration structure of the sodium and sulfate ions in the 0.1–2 M concentration range and the one-dimensional and two-dimensional potentials of mean force for the sodium–sulfate ion pairing at the low concentration limit (0.1 M), which are inaccessible to DFT. At low concentrations, the sulfate ion is strongly solvated, leading to the stabilization of solvent-separated ion pairs over contact ion pairs. Minimum energy pathway analysis revealed that coordinating two sodium ions with a sulfate ion is a multistep process whereby the sodium ions coordinate to the sulfate ion sequentially. Finally, we demonstrate that MLIPs allow the study of solvated ions beyond simple monovalent pairs with DFT-level accuracy in their low concentration limit (0.1 M) via statistically converged properties from ns-long simulations.

anions↗
DOE OSTI2021

The Deep Eutectic Solvent Precipitation Synthesis of Metastable Zn 4 V 2 O 9

A precipitation method involving a deep eutectic solvent (DES)–a mixture of hydrogen bond donor and acceptor–is used to synthesize a ternary metal oxide. Without toxic reagents, precipitates consisting of Zn 3 (OH) 2 V 2 O 7 ·nH 2 O and Zn 5 (OH) 6 (CO 3 ) 2 are obtained by simply introducing deionized H 2 O to the DES solution containing dissolved ZnO and V 2 O 5 . Manipulation of the synthetic conditions demonstrates high tunability in the size/morphology of the two-dimensional nanosheets precipitated during the dynamic equilibrium process. According to differential scanning calorimetry and high-temperature powder X-ray diffraction, Zn 3 V 2 O 8 and ZnO obtained by the annealing of the precipitate are intermediates in the reaction pathway toward metastable Zn 4 V 2 O 9 . Intimate mixing of the metal precursors achieved by the precipitation method allows access to the metastable zinc-rich vanadate with unusually rapid heat treatment. Furthermore, the UV–vis and surface photovoltage spectra reveal the presence of sub-band gap states, stemming from the reduced vanadium (V 4+ ) center. Photoelectrochemical measurements confirm weak photoanodic currents for water and methanol oxidation. For the first time, this work shows the synthesis of a metastable oxide with the DES-precipitation route and provides insight into the structure–property relationship of the zinc-rich vanadate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

ThO 2 and Th 1– x U x O 2 Nanoscale Materials and Thin Films for Nuclear Science Applications

This study investigates the dynamics and mechanisms of solution combustion synthesis (SCS) for the preparation of nanoscale ThO 2 and Th 1–x U x O 2 materials, utilizing metal nitrates (Th(NO 3 ) 4 and UO 2 (NO 3 ) 2 ) and acetylacetone (C 5 H 8 O 2 ) as reactants dissolved in a 2-methoxyethanol (C 3 H 8 O 2 ) solvent. By combining thermodynamic calculations, dynamic time–temperature profile measurements with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), this research reveals how variations in acetylacetone concentration and uranium content influence the structural parameters of the synthesized oxides. The time–temperature measurements show that the heating rate and maximum combustion temperatures are sensitive to acetylacetone concentration. DSC-TGA results indicate shifts in exothermic peak temperatures as the uranium content changes. The complexation between thorium and acetylacetone emerges as a critical factor, impacting combustion parameters and the structural characteristics of the final products. The uniform distribution of Th and U in the Th 1–x U x O 2 solid solution and the formation of nanoscale particles with strained crystallites are considered essential for the low-temperature densification of these materials for nuclear fuel pellet applications. Additionally, high-quality ThO 2 and Th 1–x U x O 2 thin (100–150 nm) films are successfully synthesized via electrospray deposition of combustible solutions followed by a brief period of heat treatment. Furthermore, these films exhibit excellent structural and morphological uniformity, making them ideal candidates for nuclear measurements, irradiation damage studies, and investigations into the physical properties of both pure and mixed oxides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

2D HSQC Chemical Shifts of Impurities from Biomass Pretreatment

Two dimensional (2D) heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) is a powerful analytical method which can be used to elucidate the structure of biomass. During processing, biomass is typically subjected to some form of chemical treatment which can be performed with a variety of compounds. The presence of these compounds, even in trace amounts, has the potential to contaminate the sample and lead to misinterpretation of the HSQC spectra. Here we report the chemical shifts of 29 compounds commonly used in biomass processing which have the potential to contaminate the biomass samples and lead to the misinterpretation of peaks associated with biomass (Populus trichocarpa ) pretreated via autohydrolysis. The identification of these chemical shifts could serve as a valuable tool in preventing errors in characterizing biomass via HSQC.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Modeling the Electronic Absorption Spectra of the Indocarbocyanine Cy3

Accurate modeling of optical spectra requires careful treatment of the molecular structures and vibronic, environmental, and thermal contributions. The accuracy of the computational methods used to simulate absorption spectra is limited by their ability to account for all the factors that affect the spectral shapes and energetics. The ensemble-based approaches are widely used to model the absorption spectra of molecules in the condensed-phase, and their performance is system dependent. The Franck–Condon approach is suitable for simulating high resolution spectra of rigid systems, and its accuracy is limited mainly by the harmonic approximation. In this work, the absorption spectrum of the widely used cyanine Cy3 is simulated using the ensemble approach via classical and quantum sampling, as well as, the Franck–Condon approach. The factors limiting the ensemble approaches, including the sampling and force field effects, are tested, while the vertical and adiabatic harmonic approximations of the Franck–Condon approach are also systematically examined. Our results show that all the vertical methods, including the ensemble approach, are not suitable to model the absorption spectrum of Cy3, and recommend the adiabatic methods as suitable approaches for the modeling of spectra with strong vibronic contributions. We find that the thermal effects, the low frequency modes, and the simultaneous vibrational excitations have prominent contributions to the Cy3 spectrum. The inclusion of the solvent stabilizes the energetics significantly, while its negligible effect on the spectral shapes aligns well with the experimental observations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Retrofitting Holcim Ste. Genevieve Cement Plant with CO2 Capture Plant Using Air Liquide Cryocap™ FG Technology

The global cement manufacturing industry is a major contributor to carbon dioxide emissions. The International Energy Agency's "Net Zero Emissions by 2050 Scenario" identifies CCS as a major strategy for meeting that goal. This project is among the first attempts to transfer capture technology developed at coal-fired power plants to the cement industry. The main objective of the project is to execute and complete a front-end engineering and design (FEED) studies for commercial-scale, carbon capture projects that separates 95% of the total CO2 emissions at the Holcim (US) Ste. Genevieve cement manufacturing facility using Air Liquide’s Pressure Swing Adsorption system (PSA) assisted Cryocap™ technology. The Holcim Ste. Genevieve cement plant in Missouri, US, boasts one of the largest single cement production lines in the world, with a capacity of approximately 12,000 t/day. The plant currently uses traditional fuels, namely coal and petcoke. The captured CO2 will be pipeline and geological storage grade. The industrial host site emits approximately 3.0 million tonne CO2/yr. Air Liquide’s Cryocap™ technology has been developed over the last 18+ years for CO2 capture applications. It has been shown to be applicable to a variety of industrial applications (e.g., steel, cement, SMR, Fluidized Catalytic Crackers (FCCs)). Cryocap™ FG consists of a Pressure Swing Adsorption (PSA) unit coupled with a Cryogenic System. The PSA pre-concentrates the CO2 from the flue gas, while the cryogenic unit enables the CO2 purity to be increased to the desired level. The project team is led by the Prairie Research Institute at the University of Illinois at Urbana-Champaign. The tasks include: complete FEED study for retrofitting the industrial facility with a carbon capture system to support developing a detailed cost estimate; business case analysis outlining the anticipated revenue and credits if projects was built and operated; technoeconomic analysis (TEA) outlining how capture system achieves DOE capture goals; and life cycle (LCA) analysis demonstrating zero net carbon emissions. The FEED study was successfully completed. This includes completing the process basis of design; preliminary engineering; outside battery limits (OSBL) detailed engineering including a Zero Liquid Discharge (ZLD) wastewater treatment system; inside battery limits (ISBL) detailed engineering [1]. An overall project capital cost estimate within a -20%/+30% accuracy was developed. The major contributors to the Total Plant Cost (TPC), by system, are the costs associated with the Outside Battery Limit (OSBL) section of the plant which includes a new river water intake structure and a Zero Liquid Discharge (ZLD) system. By cost category, the major contributors to the TPC are equipment and subcontractor costs, followed closely by engineering, construction management, home office and contractor fees. The TEA has been created to reflect the findings of the project. It analyzes the economic performance of the Cryocap™ technology by reviewing the estimated capital costs, operating cost, and revenue. The Cost of Capture (COC) associated with the Cryocap™ technology for 95% CO2 capture, when considering NETL 2018 economic assumptions (42/58 debt/equity ratio, 5.15% interest on debt and 1.42% return on equity in real dollars) and 2022 economic assumptions (42/58 debt/equity ratio, 8.82% interest on debt and 4.90% return on equity in real dollars) was found to be much lower than that for the DOE-NETL’s base-line cases. The highest contributors to the COC are annualized capital expenditures (CAPEX) and electricity consumption which can be offset by using lower cost renewable sources. The LCA was conducted using OpenLCA which is an open-source software that is recommended by NETL. The database utilized for this study was a modified version of TRACI 2.1 (developed by the US. Environmental Protection Agency’s National Risk Management Research Laboratory and modified by NETL). The Cryocap™ FG technology does not consume fuels in significant quantities and does not utilize specialized chemical solvents subject to decomposition, such as those utilized in amine-based carbon capture systems. The Cryocap™ FG technology mainly utilizes electricity as its energy input; hence, its calculated emissions are mainly associated with the generation of electricity offsite and are dependent on the energy matrix of the grid at the time of project implementation. The water consumption impact of the Cryocap™ FG is mostly for makeup of the water lost by evaporation in the cooling tower; however, the carbon capture plant will be equipped with a ZLD system to avoid effluent streams and minimize water consumption. The successful construction and operation of this plant based on this study results will provide a means to demonstrate an economically attractive and transformational capture technology that can be used to retrofit existing plants and be deployed at new plants.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2024

Influence of Annealing Temperature on the OER Activity of NiO(111) Nanosheets Prepared via Microwave and Solvothermal Synthesis Approaches

Earth-abundant transition metal oxides are promising alternatives to precious metal oxides as electrocatalysts for the oxygen evolution reaction (OER) and are intensively investigated for alkaline water electrolysis. OER electrocatalysis, like most other catalytic reactions, is surface-initiated, and the catalyst performance is fundamentally determined by the surface properties. Most transition metal oxide catalysts show OER activities that depend on the predominantly exposed crystal facets/surface structure. Therefore, the design of synthetic strategies to obtain the most active crystal facets is of significant research interest. In this work, rock salt NiO OER catalysts with (111) predominantly exposed facets were synthesized by a solvothermal (ST) method either heated under supercritical or microwave-assisted (MW) conditions. Particular emphasis was placed on the influence of the post annealing temperature on the structural configuration and OER activity to compare their catalytic performances. The as-prepared electrocatalysts are pure α-Ni hydroxides which were converted to rock salt NiO (111) nanosheets with hexagonal pores after heat treatment at different temperatures. The OER activity of the electrodes has been evaluated in 0.1 M KOH using geometric and intrinsic current densities via normalization by the disk area and BET area, respectively. The lowest overpotential at a geometric current density of 10 mA/cm 2 is found for samples pretreated by heating between 400 and 500 °C with a catalyst loading of 115 μg/cm 2 . Despite the very similar nature of the catalysts obtained from the two methods, the ST electrodes show a higher geometric and intrinsic current density for 500 °C pretreatment. The MW electrodes, however, achieve an optimal geometric current density for 400 °C pretreatment, while their intrinsic current density requires pretreatment over 600 °C. Interestingly, pretreated electrodes show consistently higher OER activity as compared to the poorly crystalline/less ordered hydroxide as-prepared electrocatalysts. Thus, our study highlights the importance of the synthesis method and pretreatment at an optimal temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Polymeric Microcapsules as Robust Mimics of Emulsion Liquid Membranes for Selective Ion Separations

Selective ion separations are increasingly needed to combat water scarcity, recover resources from wastewater, and enable the efficient recycling of electronics waste. Emulsion liquid membranes (ELMs) have received interest due to rapid kinetics, high selectivities, and low solvent requirements but are too unstable for industrial usage. Here, we demonstrate that polymeric microcapsules can serve as robust, solvent-free mimics of ELMs. As a proof of concept, we incorporated the copper-selective ligand Lix 84-I in the walls of microcapsules formed from a commercial polystyrene-b-polybutadiene-b-polystyrene triblock polymer. The microcapsules were formed from a double-emulsion template, resulting in particles typically 20–120 μm in diameter that encapsulated even smaller droplets of a dilute (≤0.5 M) H 2 SO 4 solution. Batch experiments demonstrated facilitated-transport behavior, with equilibrium reached in as little as 10 min for microcapsules with 1% ligand, and with ~15-fold selectivity for Cu 2+ over Ni 2+ . Furthermore, the microcapsules could be packed readily in columns for flow-through operation, thus enabling near-complete Cu 2+ removal in ~2 min under certain conditions, recovery of Cu 2+ by flowing through fresh dilute H 2 SO 4 , and reuse for at least 10 cycles. The approach in this work can serve as a template for using selective ligands to enable robust and simple flow-through processes for a variety of selective ion separations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Ion–ion interactions enhance aluminum solubility in alkaline suspensions of nano-gibbsite (α-Al(OH) 3 ) with sodium nitrite/nitrate

Despite widespread industrial importance, predicting metal solubilities in highly concentrated, multicomponent aqueous solutions is difficult due to poorly understood ion–ion and ion–solvent interactions. Aluminum hydroxide solid phase solubility in concentrated sodium hydroxide (NaOH) solutions is one such case, with major implications for ore refining, as well as processing of radioactive waste stored at U.S. Department of Energy legacy sites, such as the Hanford Site, Washington State. The solubility of gibbsite (α-Al(OH) 3 ) is often not well predicted because other ions affect the activity of hydroxide (OH – ) and aluminate (Al(OH) 4 – ) anions. In the study reported herein, we systematically examined the influence of key anions, nitrite (NO 2 – ) and nitrate (NO 3 – ), as sodium salts on the solubility of α-Al(OH) 3 in NaOH solutions taking care to establish equilibrium from both under- and oversaturation. Rapid equilibration was enabled by use of a highly pure and crystalline synthetic nano-gibbsite of well-defined particle size and shape. Measured dissolved aluminum concentrations were compared with those predicted by an α-Al(OH) 3 solubility model derived for simple Al(OH) 4 – /OH – systems. Specific anion effects were expressed as an enhancement factor (Al enhc ) conveying the excess of dissolved aluminum. At 45 °C, NaNO 2 and NaNO 3 -containing systems exhibited Al enhc values of 2.70 and 1.88, respectively, indicating significant enhancement. The solutions were examined by Raman and high-field 27 Al NMR spectroscopy, indicating specific interactions including Al(OH) 4 – –Na + contact ion pairing and Al(OH) 4 – –NO 2 – /NO 3 – ion–ion interactions. Dynamic evolution of the α-Al(OH) 3 particles including growth and agglomeration was observed revealing the importance of dissolution/reprecipitation in establishing equilibrium. These studies indicate that incomplete ion hydration, as a result of the low water activity in these concentrated electrolytes, results in: (i) enhanced reactivity of the hydroxide ion with respect to α-Al(OH) 3 ; (ii) increased concentrations of Al(OH) 4 – in solution; and (iii) stronger ion–ion interactions that act to stabilize the supersaturated solutions. This information on the mechanisms by which α-Al(OH) 3 becomes supersaturated is essential for more energy-efficient aluminum processing technologies, including the treatment of millions of gallons of Al(OH) 4 – -rich high-level radioactive waste.

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

Critical review of functionalized silica sorbent strategies for selective extraction of rare earth elements from acid mine drainage

We report the ubiquitous and growing global reliance on rare earth elements (REEs) for modern technology and the need for reliable domestic sources underscore the rising trend in REE-related research. Adsorption-based methods for REE recovery from liquid waste sources are well-positioned to compete with those of solvent extraction, both because of their expected lower negative environmental impact and simpler process operations. Functionalized silica represents a rising category of low cost and stable sorbents for heavy metal and REE recovery. These materials have collectively achieved high capacity and/or high selective removal of REEs from ideal solutions and synthetic or real coal wastewater and other leachate source. These sorbents are competitive with conventional materials, such as ion exchange resins, activated carbon; and novel polymeric materials like ion-imprinted particles and metal organic frameworks (MOFs). This critical review first presents a data mining analysis for rare earth element recovery publications indexed in Web of science, highlighting changes in REE recovery research foci and confirming the sharply growing interest in functionalized silica sorbents. A detailed examination of sorbent formulation and operation strategies to selectively separate heavy (HREE), middle (MREE), and light (LREE) REEs from the aqueous sources is presented. Selectivity values for sorbents were largely calculated from available figure data and gauged the success of the associated strategies, primarily: (1) silane-grafted ligands, (2) impregnated ligands, and (3) bottom-up ligand/silica hybrids. These were often accompanied by successful co-strategies, especially bite angle control, site saturation, and selective REE elution. Recognizing the need to remove competing fouling metals to achieve purified REE “baskets,” we highlight techniques for eliminating these species from acid mine drainage (AMD) and suggest a novel adsorption-based process for purified REE extraction that could be adapted to different water systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Dissolution of Fluoride Salts in Hanford Tank Waste

The Direct Feed High-Level Waste (DFHLW) strategy seeks to bypass the Hanford Waste Treatment and Immobilization Plant Pretreatment Facility while retaining some processing functions to maximize waste feed loading and minimize high-level waste (HLW) waste volume. The DFHLW flowsheet needs leaching, washing, and solids concentration operations either in new or existing tanks. The effectiveness and efficiency of sludge washing has a substantial impact on DST space, mission duration, and the evaporation and low-activity waste (LAW) treatment operations required by these large wash-water additions. One target species requiring washing is fluoride. The HLW glass composition limits for fluorine drive operations to dissolve fluoride-bearing salts into the LAW fraction and thereby maximize waste loading in HLW glass. The fluoride in many high-level wastes at Hanford is predominantly in the form of fluoride-salt precipitates: villiaumite (NaF), kogarkoite (Na 3 FSO 4 ), and natrophosphate (Na 7 F(PO 4 ) 2 ·19H 2 O). Fluoride produces melter off-gas that creates corrosion risk in the off-gas system piping, while the sulfate and phosphate in the fluoride double salts kogarkoite and natrophosphate can be detrimental to glass waste loading. Fluoride salts are sparingly soluble, with solubilities ranging from approximately 40 to 130 kg per kL of pure water, and the dissolution kinetics of the three fluoride salts are not well known. Unexpected delays in a tank dissolution process could be encountered as a result of the lack of information about dissolution rates. In addition, if the double salts show transient non-stoichiometric dissolution of fluoride versus phosphate or sulfate, unexpectedly high concentrations of one of these other constituents could be produced. Washington River Protection Solutions authorized Pacific Northwest National Laboratory to collect the available data for fluoride salt dissolution rate, provide a scoping estimate of dissolution time if possible, and identify gaps in the understanding and predictive capability for estimating dissolution time. Open literature and Hanford reports were reviewed to document, understand, and (where possible) evaluate limitations on fluoride salt equilibria and dissolution kinetics, including both mass transport and surface reaction rate. Scoping estimates of dissolution time were made for mass-transfer-controlled dissolution of spherical particles of fluoride salts suspended in liquid. This is not the only potential governing mechanism; dissolution could be substantially slower if the surface reaction rate (the rate of release of ions from the surface) is the controlling mechanism. When the minimum amount of water for complete dissolution is used and the slip velocity between the liquid and suspended particles is less than or equal to the terminal settling velocity, the estimated mass-transfer rates allow 0.1 mm particles of fluoride salt to dissolve in minutes at 25 °C in water containing no other dissolved salts. Much larger solids, such as the 6-mm chunks that have been seen in heels, could take a few hours to more than a week to dissolve. The actual dissolution times will depend strongly on the actual slip velocity, the extent of particle suspension, constraint by surface reaction rates, the ratio of solvent to solid, and the presence of common ions that shift the solubility equilibria to restrict dissolution of fluoride salts.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Separating Miscible Liquid–Liquid Mixtures Using Supported Ionic Liquid Membranes

Supported liquid membranes (SLMs) are promising in separating miscible liquid–liquid mixtures, which has been a key challenge in wastewater treatment and other applications. However, SLMs suffer from poor durability due to the loss of the liquid phase. In current work, ionic liquids (ILs) with high stability have been impregnated into polyvinylidene fluoride membranes to separate miscible benzene–heptane mixtures. The two imidazolium-based ILs, that is, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF 6 ]) and 1-butyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate ([BMIM][FAP]), were tested in supported ionic liquid membranes (SILMs) for the benzene–heptane separation. Both ILs show successful separation within 48 h as indicated by nuclear magnetic resonance results. Compared to the SILM with [BMIM][FAP], the SILM with [BMIM][PF 6 ] has lower throughput and higher selectivity. The higher selectivity can be attributed to the higher hydrophilicity of [BMIM][PF 6 ], which results in strong repulsion against heptane. The lower throughput can be attributed to the higher hydrophilicity as well since it lowers the solubility of benzene in [BMIM][PF 6 ]. The stability of IL in SILMs has also been investigated via multiple separation cycles. The scanning electron microscopy, weight change of SILMs, and separation results indicate that the separation efficiency of the [BMIM][PF 6 ] SILM does not degrade for up to 144 h. The SILM has been further optimized with curvature design (i.e., curved SILM) to increase the interfacial area and thus increase the separation throughput, where the curved SILM separation device was 3D-printed. Here, the findings here have important implications on design and application of SILMs in separating miscible liquid–liquid mixtures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗