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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nonthermal hydrogen plasma-enabled ambient, fast lignin hydrogenolysis to valuable chemicals and bio-oils

The reduction of fossil fuel resources and the ongoing surge in global energy demand have captured the interest of researchers worldwide, prompting a focus on developing renewable energy sources. For this reason, biomass conversion has emerged as a crucial pathway for renewable fuel production. Lignin, constituting 10–35% of woody biomass, represents a significant and largely untapped sustainable feedstock. Despite the potential of lignin, a substantial portion of this lignocellulosic residue remains unused, with approximately 60% considered waste. This study addresses the challenge of underutilized lignin by introducing an innovative approach to its hydrogenolysis. Despite their potential, existing hydrogenolysis methods face obstacles such as complexity, high cost, and the need for high temperatures or pressures. Herein we report a noncatalytic nonthermal hydrogen plasma method for lignin hydrogenolysis, conducted under ambient temperature and pressure conditions. Our method proves to be highly effective in breaking lignin bonds, achieving complete conversion, and generating valuable gaseous and bio-oil products including methane and aromatic dimers and monomers obtained from guaiacyl and syringyl units within the lignin structure. Our results showed an increase in gaseous products, especially methane, and aromatic monomer yields, as well as a reduction in total bio-oil and biochar yields and lignin functional groups by increasing reaction time, input power, and H2 partial pressure. This research confirms the considerable promise of utilizing noncatalytic nonthermal hydrogen plasma-assisted hydrogenolysis as an effective technique for producing gaseous and liquid fuels from lignin.

Pishva, Parsa↗
DOE OSTI2023

Chemical structure and complex growth modes of magnesium silicate hydrate: Nanoparticle orientation, aggregation, and fusion

The extent of utilization of magnesium silicate hydrate (MSH) in construction is limited partly because of insufficient data ascertaining the kinetics of its precipitation. In this report MSH grown homogeneously or heterogeneously in the range of magnesium to silicon solution molar concentration ratios, [Mg]/[Si] = 0.5-1.5, and temperature = 25-80 °C was analyzed for its chemical structure and morphology. Infrared spectroscopy and geochemical modeling show that increasing the [Mg]/[Si] ratio results in less silicate polymerization in MSH. Atomic force microscopy reveals the presence of nanoparticles that aggregate and fuse to form films. Oriented attachment of nanoparticles and features indicative of enhanced crystallinity were observed at higher temperatures and longer reaction times. These data provide direct evidence for the persistence of hierarchical structures (i.e., nanoparticles forming 3D microparticles and 2D film layers) at the nanoscale to mesoscale. These findings offer insights into the precise chemical synthesis of MSH and its widespread use as a binder for construction purposes.

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

Metal-organic-framework and walnut shell biochar composites for lead and hexavalent chromium removal from aqueous environments

Extensive research in recent years has explored the realm of porous carbon composites for various applications, including electrochemistry, structural materials, environmental remediation, and more. In particular, the fabrication of porous carbon composites using a metal-organic framework (MOF) and biochar (BC) for aqueous remediation is a fairly new avenue of research. In this study, a MOF-BC composite was synthesized with unmodified and chemically modified BCs using solvothermal synthesis. The composites were used as adsorbents to remediate heavy metals, such as lead (II) and chromium (VI), from aqueous environments. Here, it was verified that the MOF was homogeneously deposited onto the BC's surface using various material characterization techniques. Lead and chromium adsorption studies revealed a high adsorption capacity with greater than 99% removal for lead and ∼65% for chromium, respectively. Impressively, for lead, the highest observed experimental adsorption capacity of the MOF-chemically modified BC composite was 535 mg/g, compared to 240 mg/g for pristine BC. Meanwhile, the adsorption capacity of the same MOF-BC composite for chromium ions was low at 18 mg/g, compared to 80 mg/g for the chemically modified BC. The MOF-BC had a rapid adsorption rate, achieving equilibrium at only 150 min of reaction time for lead ions. MOF-BCs have higher adsorption for cationic lead through physisorption and ion-exchange mechanisms, whereas, for anionic chromium, removal is dominated only by physisorption mechanisms. The outcomes and methodological developments attained in this study offer a novel and compelling approach for synthesizing MOF-BC composites for aqueous remediation applications.

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

One-step atmospheric microplasma synthesis of an NMC-type lithium-ion battery cathode

The manufacture of battery cathode materials is the most energy-intensive step in the production of commercial lithium-ion batteries; specifically, the synthesis of the widely used transition metal oxide cathodes can require tens of hours at temperatures exceeding 700 °C. Attempts to limit the reaction time and energy required to form crystalline cathode materials often still include a heating or calcination step. This communication aims to highlight a nascent yet novel synthesis route: a one-step atmospheric microplasma process for synthesizing cathode particles in less than one second. The hollow-tube reactor employed produces crystalline particles measuring 0.1–3 μm in diameter, displays narrow XRD peaks corresponding to the 003, 104, and 101 planes, and exhibits anodic redox behavior at 3.75 V vs. lithium—characteristic of transition-metal oxide cathode materials—all without requiring an additional calcination step.

25 ENERGY STORAGE↗
DOE OSTI2020

Superior performance biodiesel from biomass-derived fusel alcohols and low grade oils: Fatty acid fusel esters (FAFE)

We demonstrated production of a superior performance biodiesel referred to here as fatty acid fusel alcohol esters (FAFE) – by reacting fusel alcohols (isobutanol, 3-methyl-1-butanol, and (S)-(-)-2-methyl-1-butanol) with oil (glyceryl trioleate) using lipase from Aspergillus oryzae. Reaction conditions corresponding to a molar ratio of 5:1 (fusel alcohols to oil), enzyme loading of 2% w/w, reaction temperature of 35 °C, shaking speed of 250 rpm, and reaction time of 24 h achieved >97% conversion to FAFE. Further, FAFE obtained from reacting a fusel alcohol mixture with corn oil were evaluated for use as a fuel for diesel engines. FAFE mixtures showed superior combustion and cold-flow properties, with the derived cetane numbers up to 4.8 points higher, cloud points up to -6 °C lower, and the heat of combustion up to 2.1% higher than the corresponding FAME samples, depending on the fusel mixture used. This represents a significant improvement for all three metrics, which are typically anti-correlated. Finally, FAFE provides a new opportunity for expanded usage of biodiesel by addressing feedstock limitations, fuel performance, and low temperature tolerance.

09 BIOMASS FUELS↗
DOE OSTI2020

Hydrothermal liquefaction of Cyanidioschyzon merolae and Salicornia bigelovii Torr.: The interaction effect on product distribution and chemistry

Hydrothermal liquefaction (HTL) has proven to be a promising technology for processing wet biomass into valuable biofuel intermediates. We investigated the influence of HTL process parameters on the individual and co-liquefaction of Salicornia bigelovii Torr. (SL) and Cyanidioschyzon merolae (CM) biomass and their respective product properties and characteristics. SL and CM biomasses were subjected to HTL conditions of process temperatures (250–350 °C), 10 wt% solid loading, 30 min reaction time, and co-liquefaction ratios (80–20, 50–50, 20–80, CM-SL, respectively). The individual maximum HTL biocrude yields for CM (34.63 wt%) and SL (7.63 wt%) were obtained at 300 °C. In both cases, biocrude oils had a higher carbon and hydrogen content relative to those of the original biomass. The HHV (higher heating value) values for the biocrude samples ranged from 24.2 to 33.12 MJ/kg, which were significantly higher than those of the original biomasses. A positive synergistic effect was observed during the co-liquefaction of two biomasses, where the experimental yield of biocrude oil was higher than the theoretical value. During the co-liquefaction experiments, a maximum biocrude yield of 32.95 wt% was obtained at 300 °C and 80–20 CM-SL biomass mix ratio. Co-liquefaction led to an increase in the energy content of the co-liquefied biocrude oil and a higher energy recovery rate. Finally, the properties of HTL products and biomasses were determined with TGA, CHN elemental analyzer, GC/MS, bomb calorimeter, HACH Spectrophotometer, and ICP OES.

09 BIOMASS FUELS↗
DOE OSTI2021

Zn uptake by illite and argillaceous rocks

The uptake of Zn by Illite du Puy (IdP) and two argillaceous rocks, Opalinus Clay (OPA) and Boda Claystone (BODA) was investigated. The uptake of Zn by illite was studied in 0.1 M NaCl at near-neutral pH and Zn loadings varying from 2.1 to 42 mmol/kg. The Zn uptake by the two argillaceous rock systems was carried out in 0.1 M NaCl at pH 7.2 and in their respective porewaters at pH 8.0 to evaluate the influence of porewater composition. The Zn loadings varied from 1.8 to 86 mmol/kg and 1.7 to 60 mmol/kg for OPA and BODA, respectively. The simplified “bottom-up approach” to predict the uptake of Zn to natural rocks with different clay mineral contents and porewater compositions was tested. This approach was found to be applicable in the argillaceous rock systems at low Zn equilibrium ([Zn] eql ) concentrations below 10 -7 M. However, at [Zn]eql above 10 -7 M, the model calculations clearly underpredicted the sorption data. The extended X-ray absorption fine structure (EXAFS) results support findings based on wet chemistry calculations using the 2 site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) sorption model. In the IdP system with prolonged reaction times of up to two years, formation of Zn precipitates was not observed. This indicates that the Zn surface complexes are stable over a time period of two years, and dissolution and recrystallization processes might not play a significant role in the Zn-IdP uptake process. In addition, the EXAFS results on illite corroborate previous findings on the existence of weak and strong sites types in dioctahedral clay minerals, as assumed in the 2SPNE SC/CE model. In the OPA and BODA systems, precipitation processes could start to begin at metal loadings of 16 mmol/kg and 24 mmol/kg, respectively. The differences between argillaceous rock samples prepared in NaCl and porewater are modest indicating that in the case of Zn the clay minerals play a predominant role in the uptake process, and that the effects originating from the porewater are minor. Furthermore, despite the differences in mineralogy, both argillaceous rocks show the same uptake behaviour, indicating that the clay minerals are predominantly responsible for the sorption at low and the precipitation processes at higher Zn concentrations. The study demonstrates how results on “pure” systems such as IdP can be transferred to predict the uptake by argillaceous rocks at low sorbate concentrations.

58 GEOSCIENCES↗
DOE OSTI2021

Mechanisms and kinetics of citrate-promoted dissolution of a uranyl phosphate mineral

The formation of uranyl phosphate precipitates is a remediation strategy to limit the mobility of uranium in contaminated soils. However, exposure to organic ligands, like the plant exudate citrate, can remobilize the uranium. The purpose of this study is to provide a more thorough comprehension of citrate-promoted dissolution of a uranyl phosphate mineral, chernikovite [(H 3 O)(UO 2 )(PO 4 )·3H 2 O], by determining the extent of uranium release from chernikovite at a wide range of citrate concentrations. Here we have quantified the kinetics of dissolution and proposed potential mechanisms of chernikovite dissolution to gain a better understanding of the fate of uranyl phosphate precipitates in the environment. Batch dissolution and continuously stirred tank reactor (CSTR) experiments indicate that increasing citrate concentrations from 0.1 mM to 50 mM increases the concentration of dissolved uranium. However, at citrate concentrations of 10 mM and greater, the effectiveness of the ligand to enhance the dissolution decreases. Density functional theory modeling and Raman spectroscopy indicate a strong interaction between citrate and the uranyl ions at the surface of the uranyl phosphate. The interaction between citrate and uranyl suggests the formation of an alteration layer of uranyl-citrate surface complexes, which could impede uranium release at citrate concentrations of 10 mM or higher. Together, these results indicate that the citrate-promoted dissolution of chernikovite is a fast reaction that is hindered by a combination of surface saturation and a secondary-phase precipitation reaction at higher concentrations of citrate and reaction times greater than or equal to 72 min based on the hydraulic residence time of CSTR experiments. These findings improve our understanding of the stability of uranyl phosphate for use in sequestration of uranium groundwater plumes at contaminated sites.

58 GEOSCIENCES↗
DOE OSTI2023

Influence of clay mineral weathering on green rust formation at iron-reducing conditions

Green rusts (GR) are important drivers for trace metal and nutrient cycling in suboxic environments. We investigated whether green rusts would incorporate aluminum (Al) or other elements from naturally-formed clay minerals containing easily-weatherable clay minerals (e.g. mica, interlayered clays). We isolated the clay minerals from a Matapeake silt loam soil by removal of silt and sand, organic matter, and reducible oxides to study mechanisms of interaction between Fe(II) and soil-sourced clay minerals. We conducted batch Fe(II) sorption experiments at multiple near-neutral pHs (6.5–7.5) and reaction times (2h–365 days). Mineral transformations were characterized by selective extractions, X-ray diffraction (XRD), and Fe X-ray absorption spectroscopy (XAS) analyzed by shell-fitting and linear combination fitting (LCF) with natural and synthetic standards. Clay mineral fraction contained a mixture of quartz, kaolinite, interlayered vermiculite, mica, and chlorite with significant structural Fe (2.6% wt). Uptake of Fe(II) increased with pH and kinetics were rapid until 5 days, followed by slow continuous Fe(II) uptake. Citrate-bicarbonate desorption kinetics from Fe(II) sorbed clay released more Al and silicon (Si) compared with unreacted soil clay fraction whereas magnesium (Mg) and potassium (K) were unaffected. Citrate-bicarbonate extracted Fe contained more Fe(II) than an ideal GR with an Fe(II)/Fe(III) molar ratio of 5.50. Analysis of the Fe EXAFS by both LCF and shell fitting was best modeled as a combination of Fe(III)-clay reduction to Fe(II) and precipitation of GR and Fe(II)-Al LDH. After 7 days of Fe(II) sorption, LCF identified 55.2% total Fe in clay, 33.4% GR(Cl) and 11.4% Fe(II)-Al LDH. Further, these results provide novel evidence of Fe(II)-Al LDHs precipitating on naturally-formed soil clay minerals as a minor phase to GR. The geochemical implications are that GRs formed in soils and sediments should be considered to have Al and Si as well as Mg substitutions affecting their structure and reactivity.

58 GEOSCIENCES↗
DOE OSTI2023

Oxidation rates and redox stabilization of ferrous iron in trioctahedral smectites

Iron(II)-bearing trioctahedral smectites (saponites) form during anoxic alteration of basaltic rock. They are predicted to have been widespread on the early Earth and are observed in the oceanic subsurface today. Smectite structures, including the occupancy of sites in the octahedral sheet, affect iron redox behavior but the rates and products of trioctahedral smectite oxidation have been largely unexplored to date. In this study we synthesized two Fe(II)-bearing trioctahedral smectites, one moderate (22 wt% Fe) and one high (27 wt% Fe) in iron content. We then examined the rate, extent, and products of their oxidation by dissolved oxygen, nitrite, and hydrogen peroxide. Dissolved oxygen caused partial oxidation of Fe(II) in the smectites with 14 to 43% of Fe(II) unoxidized after 20 to 30 days of exposure. The rate and extent of oxidation correlated with the dissolved oxygen concentration and the Fe(II) content of the clay. The incomplete oxidation in these experiments is consistent with the mixed-valent trioctahedral smectites observed in oxidized natural samples but contrasts with the complete reoxidation by oxygen shown by chemically- or microbially-reduced dioctahedral smectites. Oxidation of structural Fe(II) by 5 mmol L -1 nitrite was negligible for the moderate-iron smectite and yielded only ~17% oxidation after 54 days of reaction for the high-iron smectite. Hydrogen peroxide caused rapid and near-complete oxidation of both clays. Powder X-ray diffraction, variable-temperature Mössbauer spectroscopy, and extended X-ray absorption fine structure spectroscopy together detected no crystalline or short-range-ordered secondary phases and show that oxidized iron remained in the trioctahedral smectite structure. The recalcitrant Fe(II) pool in oxidized trioctahedral smectites exists in less distorted sites than Fe(II) in the initial clays. Its unreactive nature at prolonged reaction times indicates an elevated redox potential generated by the local coordination environment. Slower oxidation rates create a larger recalcitrant Fe(II) pool, suggesting kinetic competition between oxidation and a process involved in redox stabilization, such as electron exchange between octahedral iron sites or deprotonation of hydroxyl groups in the structure. The resistance to complete oxidation of trioctahedral ferrous smectites and their full retention of iron demonstrates that transitions from anoxic to oxic conditions generate mixed-valence smectites rather than a mixture of new phases. Identifying the diagenetic products of mixed-valent trioctahedral smectites may provide an indicator in the rock record of past redox cycling. In conclusion, substantial portions of structural Fe(II) in trioctahedral smectites display slow abiotic oxidation kinetics and represent potential electron donors for both microaerophilic iron oxidizing and nitrate-reducing, iron-oxidizing microorganisms in altered mafic rocks and related settings.

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

Engineering surface segregation of perovskite oxide through wet exsolution for CO catalytic oxidation

Cation segregation occurring near the surface or interfaces of solid catalysts plays an important role in catalytic reactions. Unfortunately, the native surface of perovskite oxides is dominated by passivated A-site segregation, which severely hampers the catalytic activity and durability of the system. To address this issue, we present a wet exsolution method to reconstruct surface segregation in perovskite cobalt oxide. Here, under reduction etching treatment of glycol solution, inert surface Sr segregation was transformed into active Co 3 O 4 segregation. By varying the reaction time, we achieved differing coverage of the active Co 3 O 4 segregation on the La 0.5 Sr 0.5 CoO 3-δ (LSCO) perovskite oxide surface. This study reveals that CO oxidation activity exhibits a volcano-shaped dependence on the coverage of Co 3 O 4 segregation at the surface of a perovskite cobalt oxide. Furthermore, we find that a suitable coverage of Co 3 O 4 segregation can dramatically improve the catalytic activity of the perovskite catalyst by enhancing interface interactions. Co K-edge, Co L-edge, and O K-edge X-ray absorption spectra confirm that the synergistic effect optimizes the covalence of the metal-oxygen bond at the surface and interface. This work not only contributes to the design of perovskite-type catalysts, but also provides important insight into the relationship between surface segregation and catalytic activity.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Influence of aluminum source and Ni/Al ratio in a batch stirred tank reactor on the structure, morphology, and electrochemical performance of Ni-rich NMA cathodes

Here, the structural, morphological, and electrochemical performance of Ni-rich LiNi 0.9 Mn 0.05 Al 0.05 O 2 (955NMA) and LiNi 0.85 Mn 0.05 Al 0.1 O 2 (85,510) cathodes strongly depends on the properties of their hydroxide precursors. Ni-Mn-Al hydroxide precursors were synthesized through controlled co-precipitation in a batch stirred tank reactor, where pH, reaction time, metal-ion feed rate, aluminum source, and aluminum concentration were systematically varied to tailor particle morphology, phase composition, and dopant distribution. Two aluminum sources, aluminum nitrate and sodium aluminate produced two distinct hydroxide precursors NMA(OH) 2 -1 and NMA(OH) 2 -2, which were lithiated to form LiNMA1 (Li 0.992 [Ni 0.905 Mn 0.049 Al 0.046 ]O 2 ) and LiNMA2 (Li 0.990 [Ni 0.850 Mn 0.047 Al 0.103 ]O 2 ). Structural and compositional analyses revealed that aluminum incorporation and phase formation in Ni–Mn–Al hydroxides are governed by local supersaturation and interfacial growth kinetics. Rapid dilute aluminum addition produced aluminum-free β-phase hydroxides, intermediate conditions generated mixed α/β phases, whereas slow concentrated dosing enabled uniform aluminum incorporation and stabilization of the β-phase structure. LiNMA1 delivers a high initial discharge capacity of 223 mAhg −1 but significant capacity fading with 67% retention after 100 cycles, associated with structural instability. In contrast, LiNMA2 delivers a lower initial capacity 172 mAhg −1 yet excellent cycling stability 91% retention, attributed to improved TM–O framework stability and reduced cation disorder.

Capacity↗
DOE OSTI2026

Engineering acid-base active sites on an N-doped biochar catalyst for microwave-assisted biodiesel production from waste cooking oil

Acid-base bifunctional catalysts play a crucial role in converting high-free fatty acid (FFA) feedstocks into biodiesel by enabling the simultaneous esterification and transesterification of triglycerides in a single step, thereby minimizing saponification and streamlining the process. In this study, we report the design and development of a novel N-doped acid-base bifunctional biochar catalyst synthesized from renewable biomass precursors- glucose and chitosan. The catalyst’s acidic sites were introduced via surface functionalization with o-sulfobenzoic acid cyclic anhydride, grafting -SO₃H groups onto the carbon framework, while basic sites were generated from amine functionalities (-NH) derived from chitosan, yielding a robust and truly bifunctional surface. The catalyst was characterized and used for the microwave-assisted transesterification of waste cooking oil, and process optimization using response surface methodology (RSM-CCD) yielding a maximum biodiesel yield of 98.8 ± 0.4% under optimal conditions (methanol-to-oil molar ratio 20:1, catalyst loading 5.7 wt%, temperature 99 °C, and reaction time 46.6 min). The catalyst demonstrated good stability, maintaining a yield of 92.2 ± 0.4% after eight reuse cycles. A Life Cycle Assessment (LCA) conducted for 1 kg of biodiesel production revealed a global warming potential of 0.85 kg CO 2 eq and human toxicity potential of 1.59 kg 1,4-DB eq, with the largest environmental contributions arising from catalyst preparation and reuse. In conclusion, this work highlights a green and circular approach to biodiesel production, combining renewable catalyst design, waste feedstock utilization, and quantitative sustainability assessment to guide future developments in sustainable catalysis and biofuel engineering.

Bifunctional catalyst↗
DOE OSTI2021

New concept of radiolytic synthesis of gold nanoparticles in continuous flow

Radiolytic synthesis has been used to produce a plethora of unsupported and supported metallic nanoparticles in batch. As proof of a new concept, we evaluated the formation of gold nanoparticles by radiolytic synthesis in continuous flow using a millifluidic reactor. A mixture of gold ions solution, branched polyethyleneimine, and ethylene glycol yielded gold nanoparticles with a mean size of 3.4 ± 1.0 nm after irradiation with an X-ray irradiator (127 Gy/min) at an absorbed dose of 5.1 kGy. The morphology and size distribution of gold nanoparticles was influenced by AgNO 3 , where its absence resulted in a mean size of 20.9 ± 15.8 nm. The radiolytic synthesis of gold nanoparticles in continuous flow was achieved in short reaction times (<60 min), at room temperature, and with low concentrations of both stabilizing and reducing agents. Furthermore, these results demonstrate the potential of radiolytic synthesis in continuous flow for high-throughput formation of metallic nanoparticles with controlled specifications in size and distribution.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Multilevel Analysis of Electrochemically Mediated Methanolysis of Poly(ethylene terephthalate) (PET)

Here, this study presents a multilevel analysis of electrochemically mediated methanolysis as a promising method for reducing the environmental impacts of plastic recycling, with a focus on depolymerizing poly(ethylene terephthalate) (PET) into dimethyl terephthalate (DMT). Instead of conventional chemical PET depolymerization, this electrochemical approach provides distinct technical advantages in process control and efficiency. At the process level, key operational parameters, including applied current and reaction time, were systematically investigated to optimize PET conversion and DMT selectivity. The electrochemical approach was directly compared to equivalent chemical methanolysis systems and demonstrated superior performance in terms of PET conversion and DMT selectivity. Building on these findings, a technoeconomic assessment identified the current economic bottlenecks and revealed that improvements in process design, DMT selectivity, PET conversion, and energy efficiency are key to reducing the overall process cost and enabling future implementation. While further optimization is required for market competitiveness, these results establish a performance baseline for the electrochemically mediated PET methanolysis process and underscore the importance of combining process-level innovation with systems-level evaluation in the development of sustainable recycling technologies.

chemical recycling↗
DOE OSTI2022

Flow-Assisted Selective Mineral Extraction from Seawater

The sustainable production of critical materials from natural sources requires a paradigm shift away from currently used resource-intensive processes. In this paper, we report a single-step, laminar co-flow method (LCM) that leverages non-equilibrium conditions to selectively extract pure Mg(OH) 2 from natural seawater. Conventional seawater-based Mg extraction involves adding individual or a combination of precipitants to obtain Mg(OH) 2 , but the co-existence of Ca 2+ unavoidably results in CaCO 3 impurities requiring additional purification steps. Here we show that the non-equilibrium conditions in LCM achieved using a microfluidics device and by simply co-injecting a NaOH solution with seawater can result in improved selectivity for Mg(OH) 2 unlike in conventional bulk mixing method. The resulting precipitates are characterized for composition and the process yield and purity are optimized through systematic variations of the reaction time and the concentration of NaOH. This is the first demonstration of LCM for selective separation, and as a one-step process that does not rely on novel sorbents, membranes, or external stimuli, it is easy to scale-up. LCM has the potential to be broadly relevant to selective separations from complex feed streams and diverse chemistries—enabling more sustainable materials extraction and processing.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Solid-State Recrystallization Pathways of Sodium Aluminate Hydroxy Hydrates

Crystallization of Al-bearing solid phases from highly alkaline Na 2 O:Al 2 O 3 :H 2 O solutions commonly necessitates an Al 3+ coordination change from tetrahedral to octahedral, but intermediate coordination states are often difficult to isolate. Here, a similar Al 3+ coordination change process is examined during the solid-state recrystallization of sodium oxohydroxoaluminate hydrate (MSA) to nonasodium bis(hexahydroxy aluminate) trihydroxide hexahydrate (NSA) at ambient temperature. While the MSA structure contains solely polymerized tetrahedral Al 3+ , the NSA structure is a molecular aluminate salt solely based upon monomeric octahedral Al 3+ . Spontaneous recrystallization of MSA and excess sodium hydroxide hydrate into NSA over 3 days of reaction time was clearly evident in X-ray diffractograms and in Raman spectra. In situ 27 Al multiple quantum MAS NMR spectroscopy showed no evidence of intermediate aluminates, suggesting that intermediates, such as pentacoordinate Al 3+ , are short-lived and require more highly time resolved spectroscopies to detect. Such research is advancing upon detailed mechanistic understanding of Al 3+ coordination change mechanisms in these highly alkaline systems, with relevance to aluminum refining, corrosion sciences, and nuclear waste processing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗