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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 OSTI2025

Recovery of Scandium from Bauxite Residue Using Sulfation Roasting-Assisted Water Leaching Process

Here, this study presents a method for recovering scandium from Indonesian bauxite residue (red mud) through a sulfation roasting-assisted water leaching process. Ammonium sulfate, (NH 4 ) 2 SO 4 , was chosen as the sulfate source for its lower melting point, less corrosivity, decreased toxicity, and the potential for ammonia recovery. A modified mixing system was introduced to improve the distribution of (NH 4 ) 2 SO 4 on red mud particles by combining them in water. A series of experiments were conducted to optimize the sulfation roasting process by examining the effects of the (NH 4 ) 2 SO 4 /red mud ratio, temperature, and roasting time. Subsequently, water leaching was optimized while considering the effect of leaching time and liquid-to-solid (L/S) ratio. The leaching of scandium from the roasted red mud showed rapid kinetics, even when using only water. Under the roasting conditions of 1/1 (g/g) (NH 4 ) 2 SO 4 /red mud ratio, 700°C, 60 min roasting time, and the leaching conditions of 65°C, 60 min, and 10 mL/g (L/S), over 90% of scandium was recovered, along with 64.4% Al leaching and below 8% Fe leaching. These results were further corroborated through comprehensive analyses such as x-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). This study offers insights into an alternative, more environmentally friendly method for Sc recovery from red mud, promoting the sustainable use of hazardous waste like red mud.

ammonium sulfate↗
DOE OSTI2020

Concentration and Recovery of Rare Earth Elements from Eastern US Coal Refuse

Recent studies funded by the US Department of energy have shown that coal and coal byproducts contain elevated contents of Rare Earth Elements (REEs), making them a potential resource for these critical materials. The approach employed in this research focused on the concentration and extraction of REEs from fine coal refuse derived from various preparation plants in the Appalachian coal basin of the United States. Initial efforts in this research focused on the identification and characterization of REEs in various fine coal refuse streams from nine distinct industrial preparation plants in Appalachia. The average REE content in these materials was determined to be approximately 200 ppm, but the REE content showed a strong correlation to the aluminum content, suggesting that the REEs are closely associated with the clay minerals present in the refuse. Given the relatively low REE concentrations, initial efforts sought to concentrate the REEs through decarbonization and dispersive liberation steps. In these tests, high-shear agitation in the presence of a polyelectrolyte, followed by sedimentation was able to isolate the REE-enriched fine clay particles from siliceous gangue minerals. Following the dispersive liberation step, all samples were found to have an REE content greater than 300 ppm, a benchmark used for many initial exploratory studies. In one case, the REE content was increased by more than 125%. Subsequent extraction tests initially utilized a direct ion-exchange leaching approach with ammonium sulfate as lixiviant. In all cases, the simple ion-exchange leaching process failed to recover significant quantities of rare earth elements, ultimately suggesting that the REEs in fine coal waste may be passivated or bound in a colloidal phase. To access this colloidal phase, several alternative approaches were evaluated, including leaching with alternative ion-exchange lixiviants, reductive leaching, gas-purged leaching, and others. The approach that showed the most promise was strong alkaline pretreatment, followed by ion-exchange leaching with ammonium sulfate at pH 4. A combination of strong alkali and high-temperatures treatment successfully liberated the REEs, converting them to a form amenable to ion-exchange leaching. The highest REE recovery achieved with this method was determined to be 39%. Lastly, bench-scale solvent extraction tests were used to further concentrate REEs in the leach solution and demonstrate that mixed rare earth concentrates can be successfully produced from fine coal refuse.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2023

Observationally Constrained Modeling of the Reactive Uptake of Isoprene-Derived Epoxydiols under Elevated Relative Humidity and Varying Acidity of Seed Aerosol Conditions

Isoprene is the non-methane volatile organic compound (VOC) emitted in largest amounts to the atmosphere, and it is a significant source of secondary organic aerosol (SOA) mass. The uptake of isoprene oxidation products followed by multiphase chemistry in fine particles is the key pathway to form isoprene epoxydiol-derived SOA (IEPOX-SOA). However, many parameters that relate to diffusion and reaction of IEPOX in the particle phase remain uncertain, since reaction kinetics previously measured in bulk aqueous phase solutions might be different from atmospheric aerosols. Here, we use simultaneous environmental chamber measurements of multiple parameters governing IEPOX-SOA formation at timescales of ~hours: particle size distribution, composition, and volatility of IEPOX-SOA to constrain the key parameters governing IE-POX-SOA formation under humid (i.e., 50% relative humidity, RH) and varying seed aerosol acidity conditions. Reducing the 2-methyltetrol (tetrol) reaction rate constants by a factor of 4 brings the model predictions in agreement with the IEPOX-SOA measurements with acidified ammonium bisulfate seed aerosols. For less acidic ammonium sulfate aerosols both the organo-sulfate (OS) and tetrol reaction rate constants need to be reduced to bring model predictions closer to chamber observations. Using the measured non-volatile content of IEPOX-SOA we constrain the oligomerization timescale of 2-methyltetrols. We find that the oligomerization timescale is 4 hours with acidified seed aerosols, but a much longer time scale of 24 hours is needed for non-acidified seed aerosols, indicating that the aerosol acidity greatly affects the oligomerization rate of tetrols. Here we show that the actual kinetics of IEPOX-SOA formation rate on aerosol seeds consisting of both ammonium bisulfate and ammonium sulfate are a factor of 4~5 slower under 50-60% RH conditions compared to their application in previous models, which were based on bulk aqueous solution measurements.

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

Southern Great Planes Aerosol Chemical Speciation Data

The data files consist of ACSM speciated mass loadings in ug m-3. The speciea reported are nitrate, sulfate, ammonium, organics, and chloride. Mass loadings are calculated with a collection efficiency of 1 pending further research into the composition dependance of the collection efficiency.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Metal Oxide Particles as Atmospheric Nuclei: Exploring the Role of Metal Speciation in Heterogeneous Efflorescence and Ice Nucleation

Mineral dust can indirectly impact climate by nucleation of atmospheric solids, for example, by heterogeneously nucleating ice in mixed-phase clouds or by impacting the phase of aerosols and clouds through contact nucleation. The effectiveness toward nucleation of individual components of mineral dust requires further study. Here, the nucleation behavior of metal oxide nanoparticle components of atmospheric mineral dust is investigated. A long-working-distance optical trap is used to study contact and immersion nucleation of ammonium sulfate by transition-metal oxides, and an environmental chamber is used to probe depositional ice nucleation on metal oxide particles. Previous theory dictates that ice nucleation and heterogeneous nucleation of atmospheric salts can be impacted by several factors including morphology, lattice match, and surface area. Here, we observe a correlation between the cationic oxidation states of the metal oxide heterogeneous nuclei and their effectiveness in causing nucleation in both contact efflorescence mode and depositional freezing mode. In contrast to the activity of contact efflorescence, the same metal oxide particles did not cause a significant increase in efflorescence relative humidity when immersed in the droplet. In conclusion, these experiments suggest that metal speciation, possibly as a result of cationic charge sites, may play a role in the effectiveness of nucleation that is initiated at particle surfaces.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Infrared Optical Constants from Pressed Pellets of Powders: I. Improved n and k Values of (NH4)(2)SO(4)from Single-Angle Reflectance

In combination with other parameters, the real, n(?), and imaginary, k(?), components of the complex refractive index, = n + ik, can be used to simulate the optical properties of a material in different forms, e.g. its infrared spectra. But obtaining reliable values of the optical constants n/k for solid materials is challenging due to the lack of optical quality specimens, usually crystals, large enough to measure. An alternative to crystals is to press the powder into a uniform disk. We have produced pellets from ammonium sulfate, (NH4)2SO4, powder and derived the pellets’ n and k values via single-angle reflectance using a specular reflectance device in combination with a Fourier transform infrared spectrometer. The single-angle technique measures amplitude of light reflected from the material as a function of wavelength over a wide spectral domain; the optical constants are determined from the reflectance data using the Kramers-Kronig relationship. We investigate several parameters associated with the pellets and pellet formation and their effects upon delivering the most reliable n/k values. Parameters studied include pellet diameter, mass and density (void space), drying, grinding, sieving and particle size in the pellet formation, as well as pressing pressure and duration. Of these parameters, using size-selected mixtures of dried, small (< 100 µm) particles and pressing at = 10 tons for at least 30 minutes were found key to forming highly reflective samples. Comparison to two sets of previous literature n(?) and k(?) values obtained from crystalline (NH4)2SO4 both as crystal reflectance as well as extinction spectra of aerosols measured in a flow tube show reasonable agreement, but suggests the present values, as confirmed from two independent techniques, represent a substantial improvement for n/k values for (NH4)2SO4, also demonstrating promise to measure the optical constants of other materials.

Optical constants, index of refraction, single-ang↗
DOE OSTI2025

A novel methodology for assessing the hygroscopicity of aerosol filter samples

Abstract. Due to US regulations, concentrations of hygroscopic inorganic sulfate and nitrate have declined in recent years, leading to an increased importance of the hygroscopic nature of organic matter (OM). The hygroscopicity of OM is poorly characterized because only a fraction of the multitude of organic compounds in the atmosphere is readily measured, and there is limited information on their hygroscopic behaviors. Hygroscopicity of aerosol is traditionally measured using a humidified tandem differential mobility analyzer (HTDMA) or electrodynamic balance (EDB). EDB measures water uptake by a single particle. For ambient and chamber studies, HTDMA measurements provide water uptake and particle size information but not chemical composition. To fill this information gap, we developed a novel methodology to assess the water uptake by particles collected on Teflon filters. This method uses the same filter sample for both hygroscopicity measurements and chemical characterization, thereby providing an opportunity to link the measured hygroscopicity with ambient particle composition. To test the method, hygroscopic measurements were conducted in the laboratory for ammonium sulfate, sodium chloride, glucose, and malonic acid, which were collected on 25 mm Teflon filters using an aerosol generator and sampler. Constant-humidity solutions (CHSs), including potassium chloride, barium chloride dihydrate, and potassium sulfate, were employed in a saturated form to maintain the relative humidity (RH) at approximately 84 %, 90 %, and 97 % in small chambers. Our preliminary experiments revealed that, without the pouch, water uptake measurements were not feasible due to rapid water loss during weighing. Additionally, we observed some absorption by the aluminum pouch itself. To account for this, concurrent measurements were conducted for both the loaded and the blank filters at each RH level. Thus, the dry loaded and blank Teflon filters were placed in aluminum pouches with one side open and in RH-controlled chambers for more than 24 h. The wet loaded samples and wet blanks were then weighed using an ultramicrobalance to determine the water uptake by the respective compound and the blank Teflon filter. The net amount of water absorbed by each compound was calculated by subtracting the water uptake of the blank filter from that of the wet loaded filter. Hygroscopic parameters, including the water-to-solute (W / S) ratio, molality, mass fraction solute (mfs), and growth factors (GFs), were calculated from the measurements. The results obtained are consistent with those reported by the Extended Aerosol Inorganics Model (E-AIM) and previous studies utilizing HTDMA and EDB for these compounds, highlighting the accuracy of this new methodology. This new approach enables the hygroscopicity and chemical composition of individual filter samples to be assessed so that in complex mixtures, such as chamber and ambient samples, the total water uptake can be parsed between the inorganic and organic components of the aerosol.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

The Bear Brook Watershed in Maine: Multi-Decadal Whole-Watershed Experimental Acidification

The Bear Brook Watershed in Maine (BBWM) is a long-term research site established to study the response of forest ecosystem function to environmental disturbances of chronic acidic deposition and ecosystem nitrogen enrichment. Starting in 1989, the West Bear (treated) watershed received bimonthly applications of ammonium sulfate [(NH4)2SO4] fertilizer from above the canopy, whereas East Bear (reference) received ambient deposition. The treatments were stopped in 2016, marking the beginning of the recovery phase. Research at the site has focused on soils, streams, and vegetation. Here, we describe data collected over three decades at the BBWM—input and stream output nutrient fluxes, quantitative soil pits and soil chemistry, and soil temperature and moisture.

Patel, Kaizad F.↗
DOE OSTI2023

Nutrients strengthen density dependence of per-capita growth and mortality rates in the soil bacterial community

Density dependence in an ecological community has been observed in many macro-organismal ecosystems and is hypothesized to maintain biodiversity but is poorly understood in microbial ecosystems. Here, in this study, we analyze data from an experiment using quantitative stable isotope probing (qSIP) to estimate per-capita growth and mortality rates of bacterial populations in soils from several ecosystems along an elevation gradient which were subject to nutrient addition of either carbon alone (glucose; C) or carbon with nitrogen (glucose + ammonium-sulfate; C + N). Across all ecosystems, we found that higher population densities, quantified by the abundance of genomes per gram of soil, had lower per-capita growth rates in C + N-amended soils. Similarly, bacterial mortality rates in C + N-amended soils increased at a significantly higher rate with increasing population size than mortality rates in control and C-amended soils. In contrast to the hypothesis that density dependence would promote or maintain diversity, we observed significantly lower bacterial diversity in soils with stronger negative density-dependent growth. Here, density dependence was significantly but weakly responsive to nutrients and was not associated with higher bacterial diversity.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

A study of rare earth ion-adsorption clays: The speciation of rare earth elements on kaolinite at basic pH

Synthesized rare earth ion-adsorption clays (La, Ce, Nd, Dy and Y, ~ 400 ppm each) were prepared from kaolinite at various basic pH in open-air conditions. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) were used to characterize the effect of pH on the adsorption mechanism of rare earth elements (REEs) on kaolinite. The crystal structure of kaolinite by XRD analysis is not altered after REE adsorption, suggesting that REEs are bound to the surface of kaolinite. Elemental analysis by XPS and ICP-MS show that the surface concentration of REEs on kaolinite is pH dependent, and a local maximum of the surface concentration is achieved at pH 10. Three characteristics of the La 3d 5/2 XPS photoemission feature were measured and compared to those of standard La compounds to probe the speciation of REEs, and electrostatically bound hydroxides such as REE(OH) 2 + are identified as the primary species on the surface of kaolinite. Finally, compared to the typical ion-adsorption clays with intrinsic acidic pH, clays synthesized at basic pH exhibit similarly high rare earth ion-exchange efficiency with ammonium sulfate (AS), suggesting that rare earth ion-adsorption clays can exist in both acidic and basic environments.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Evaluation of assumptions made by Hygroscopic Tandem Differential Mobility Analyzer inversion routines

The Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) measures the hygroscopicity of atmospheric particles, and many atmospheric processes that change this hygroscopicity also change the atmospheric size distribution. Two assumptions made during H-TDMA inversion create spurious hygroscopic trends as a function of the changing inlet size distribution. These two assumptions—that the particles exiting the first Differential Mobility Analyzer (DMA1) are singly charged and that the inlet size distribution has a slope of zero (flat)— generate Multi-Charge Dispersion (MCD) bias and Slope bias, respectively. First, we use a model, named TAO, to show that the inlet size distribution could theoretically change the measured ammonium sulfate hygroscopicity by 10%–20% as a function of diameter or experimental time with no change in relative humidity. Secondly, we show experimentally that aerosol emitted from the flaming combustion of grass creates MCD bias. Here, in this experiment, we measure the CPC response of the first three charges and invert these responses using a new routine named Junior. Junior's inversion of each charge shows that one growth factor distribution describes all measured diameters (no growth dependence on diameter). As in the modeling study above, previous publications of this aerosol system, using traditional inversion assumptions, report a decrease in hygroscopicity as DMA1 diameter increases. Unlike traditional inversions, Junior's inversion does not assume the particles are singly charged nor does it make the flat inlet size distribution assumption. Instead, both the inlet size distribution and each charge's CPC response are measured quantities. Thus, the discrepancy between our inversion results and previous publications is likely due to the traditional inversion routine assumptions. This underscores the importance for accounting for Slope and MCD bias during inversions. Experimental results should be carefully analyzed when reporting hygroscopic trends with respect to diameter or experimental time when using the traditional inversion assumptions.

42 ENGINEERING↗
DOE OSTI2022

Development of a chemical-free process utilizing ozone oxidative precipitation for the recovery of cobalt and manganese from acid mine drainage

Acid mine drainage (AMD) has been identified as a viable secondary resource of Co, and Mn. However, recovery of these elements while treating AMD is challenging due to the unfavorable pH and Eh conditions for Co-Mn precipitation. This study investigated the effects of various ligands (hydroxide, carbonate, ammonium, sulfate, and phosphate) and oxidizers (sodium persulfate, potassium permanganate, and ozone) on the precipitation of Co-Mn from AMD through experimental and solution chemistry studies. Ozone was found to be the most effective agent for the recovery of these elements. Based on the results, an AMD treatment process was formulated for selective recovery of multiple critical elements, including Al, REEs, Co, and Mn. More than 95 % of Co and Mn were recovered through the proposed process utilizing chemical-less ozone oxidative precipitation. In conclusion, a precipitate containing 0.9 % Co and 54.6 % Mn was obtained from an AMD source containing 0.9 ppm Co and 41.8 ppm Mn.

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

Liquid–Liquid Phase Separation in Supermicrometer and Submicrometer Aerosol Particles

The interactions of aerosol particles with light and clouds are among the most uncertain aspects of anthropogenic climate forcings. The effects of aerosol particles on climate depend on their optical properties, heterogeneous chemistry, water uptake behavior, and ice nucleation activity. These properties in turn depend on aerosol physics and chemistry including composition, size, shape, internal structure (morphology), and phase state. The greatest numbers of particles are found at small, submicrometer sizes, and the properties of aerosol particles can differ on the nanoscale compared with measurements of bulk materials. As a result, our focus has been on characterizing the phase transitions of aerosol particles in both supermicrometer and submicrometer particles. The phase transition of particular interest for us has been liquid–liquid phase separation (LLPS), which occurs when components of a solution phase separate due to a difference in solubilities. For example, organic compounds can have limited solubility in salt solutions especially as the water content decreases, increasing the concentration of the salt solution, and causing phase separation between organic-rich and inorganic-rich phases. To characterize the systems of interest, we primarily use optical microscopy for supermicrometer particles and cryogenic-transmission microscopy for submicrometer particles. This Account details our main results to date for the phase transitions of supermicrometer particles and the morphology of submicrometer aerosol. Herein, we have found that the relative humidity (RH) at which LLPS occurs (separation RH; SRH) is highly sensitive to the composition of the particles. For supermicrometer particles, SRH decreases as the pH is lowered to atmospherically relevant values. SRH also decreases when non-phase-separating organic compounds are added to the particles. For submicrometer particles, a size dependence of morphology is observed in systems that undergo LLPS in supermicrometer particles. In the limit of slow drying rates, particles <30 nm are homogeneous and larger particles are phase-separated. This size dependence of aerosol morphology arises because small particles cannot overcome the activation barrier needed to form a new phase when phase separation occurs by a nucleation and growth mechanism. Additionally, the inhibition of LLPS in small particles is observed for mixtures of ammonium sulfate with single organic compounds as well as complex organics like α-pinene secondary organic matter. The morphology of particles affects activation diameters for the formation of cloud condensation nuclei. These results more generally have implications for aerosol properties that affect the climate system. In addition, LLPS is also widely studied in materials and biological chemistry, and our results could potentially translate to implications for these fields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Nonequilibrium Behavior in Isoprene Secondary Organic Aerosol

Recent studies have shown that instantaneous gas-particle equilibrium partitioning assumptions fail to predict SOA formation, even at high relative humidity (~85%), and photochemical aging seems to be one driving factor. In this study, we probe the minimum aging time scale required to observe nonequilibrium partitioning of semivolatile organic compounds (SVOCs) between the gas and aerosol phase at ~50% RH. Seed isoprene SOA is generated by photo-oxidation in the presence of effloresced ammonium sulfate seeds at <1 ppbv NO x , aged photochemically or in the dark for 0.3–6 h, and subsequently exposed to fresh isoprene SVOCs. Our results show that the equilibrium partitioning assumption is accurate for fresh isoprene SOA but breaks down after isoprene SOA has been aged for as short as 20 min even in the dark. Modeling results show that a semisolid SOA phase state is necessary to reproduce the observed particle size distribution evolution. The observed nonequilibrium partitioning behavior and inferred semisolid phase state are corroborated by offline mass spectrometric analysis on the bulk aerosol particles showing the formation of organosulfates and oligomers. Here, the unexpected short time scale for the phase transition within isoprene SOA has important implications for the growth of atmospheric ultrafine particles to climate-relevant sizes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Revisiting the Effects of Seed Liquid Water Content on Isoprene Secondary Organic Aerosol Growth

Aerosol liquid water content (LWC) has been shown to enhance partitioning of water-soluble oxygenated organic vapors into the aerosol particles and facilitate aqueous chemistry, impact SOA formation, composition, and physicochemical properties. Here, this study examines the effect of aerosol liquid water content (LWC) on isoprene SOA formation using effloresced and deliquesced ammonium sulfate ((NH 4 ) 2 SO 4 ) and sodium chloride (NaCl) seed particles in an environmental chamber with photo-oxidation extending over hours under moderate relative humidity (50%-60%). Our findings indicate that isoprene SOA mass yield is not significantly influenced (p value >> 0.05) by the phase state or the chemical identity of the seed particles within a 3–4-hour reaction time scale. Detailed molecular analysis using advanced high resolution mass spectrometry indicates that while both effloresced and deliquesced seed types produced similar molecular formula distributions, deliquesced (NH 4 ) 2 SO 4 slightly favored the production of less volatile compounds. Depth-profiling analysis by single particle mass spectrometry confirmed that isoprene SOA predominantly located on the surfaces of particles with core-shell morphologies, with partial dissolution of the effloresced inorganic salt observed even below the deliquescence relative humidity (DRH) of salt. This finding suggests that assuming dry salt core particles do not interact with SOA coatings, based on salt deliquescence points, may overlook important aqueous chemistry. These results emphasize the critical role of reaction time scale and mixing state on SOA formation and call for further research to understand LWC effects on SOA from different precursors.

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

Influence of Gel Formation on the Heterogeneous Oxidation of Organic Aerosol

Recent work has shown that divalent cations can perturb the viscosity and phase state of oxygenated organic particles in unexpected ways, sometimes leading to the formation of gel states. Despite the prevalence of divalent cations and oxygenated organic molecules in atmospheric aerosol, particularly in marine environments, the influence of gel states on the reaction rates is not well established. Here, in this work, we measure and compare the impact of viscosity and gel formation on the ozonolysis chemistry of aerosol particles containing the unsaturated, oxygenated organic species ascorbic acid (AA). AA serves as an excellent proxy compound for highly oxidized molecules in the atmosphere. We measured the hygroscopic growth, phase state, viscosity, and water diffusion rate in binary particles containing AA and water and in ternary particles with an additional co-solute of either ammonium sulfate or CaCl 2 . These measurements reveal gel formation in particles mixed with CaCl 2 , as particles become rigid but allow for relatively rapid diffusion rates of water, consistent with previous observations of gel behavior. We measured the rate of ozonolysis of these particles under a range of relative humidity (RH) conditions, showing a clear decrease in the rate with decreasing RH, consistent with the increase in viscosity and slowed diffusion. Notably, we measured the rate of ozonolysis of particles existing in a gel state, showing that following an initial period of decay, the rate of reaction arrests, indicating that the organic material in the solid state is protected from the reaction. This work shows that viscous particles and gel particles exhibit different reactivity toward heterogeneous oxidants, with significant implications for how we understand the chemical evolution of aerosol particles in the atmosphere.

gels↗
DOE OSTI2025

Predicting Liquid–Liquid Phase Separation of Submicrometer Proxies for Atmospheric Secondary Aerosol

Liquid–liquid phase separation (LLPS) of atmospheric aerosols can significantly impact climate, air quality, and human health. However, their complex composition, small size, and history-dependent properties result in great uncertainty in the modeling of aerosol phase state and atmospheric processes. Herein, using cryogenic transmission electron microscopy (cryo-TEM), we examined model submicron aerosols composed of organic compounds and ammonium sulfate, and established a parameterization for the separation relative humidity (SRH) that accounts for chemical composition, particle size, and equilibration time. We evaluated different variables that describe chemical composition: O/C ratio, partition coefficient, solubility, molar mass, and polarizability. The O/C ratio fits the SRH of micrometer droplets best, and by using a scaling factor to translate the micrometer SRH parameterization to submicron aerosols, we incorporate the effects of size and equilibration time. The measured scaling factor for the submicron mean SRH (30nm – 1μm, 20 min equilibration times) is 0.80, the factor becomes 1 with equilibration time over 1 hour, and is equal to 0, meaning that SRH is absent, when the aerosol dry diameter is smaller than 30 nm. Furthermore, our parameterization will aid in universal SRH modeling, potentially leading to more accurate predictions of aerosol mass, optical properties, hygroscopicity, and heterogeneous chemistry.

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

Membrane Contactors for Ammonia Recovery from Anaerobic Digester Centrate: Pretreatment and Process Optimization

Haber-Bosch process allows for the production of modern fertilizers and is crucial for meeting increasing demands for agricultural production. The process requires large amounts of natural gas and contributes to global warming. An alternative to the Haber-Bosch process utilizes membrane contactors to recover nitrogen from the anaerobic digester centrate. In previous studies, high recoveries have been achieved, but membrane fouling decreased the performance and required maintenance to clean the membranes. Furthermore, this study investigated the effect of a settling and ultrafiltration system to pretreat centrate from an anaerobic digester to prevent fouling of the membrane contactor system. The system achieved high recoveries of over 90% for 10 cycles without any performance decline. Tests with increasing distillate concentrations of ammonium sulfate up to 165,000 mg/L-N could not identify a significant decline in membrane performance either. This allows for concentration up to crystallization in a single stage.

09 BIOMASS FUELS↗