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At least 685 records · Page 38

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DOE OSTI2016

Microstructure evolution during the precipitation and growth of fully coherent DO{sub 22} superlattice in an Ni-Cr-W alloy

The ordering transformation occurring in a model Ni-Cr-W superalloy during prolonged exposure to proper temperature has been investigated systematically. It is demonstrated that nanometer-sized precipitates with a DO{sub 22} structure can precipitate in the Ni-Cr-W alloy by means of simple aging treatment at 650–700 °C. The mechanism of transformation to DO{sub 22} superlattice has been determined to be continuous ordering based on the results of high resolution transmission electron microscopy investigation and variation trend in Vickers microhardness. Different variants of DO{sub 22} phase can coexist in the matrix with no signs of overaging as aging time increases, indicating it has a high thermal stability. The precipitates of DO{sub 22} superlattice has been found to be of ellipsoidal shape which results in the greatest reduction of strain energy. The interfaces between DO{sub 22} precipitates and matrix have been revealed to be coherent at the atomic scale, resulting in considerable coherency strain attributing to the lattice misfit between DO{sub 22} particle and matrix. Because of the high-density nanometer-sized DO{sub 22} phase, the microhardness of the alloy has been improved remarkably after aging treatment. - Graphical abstract: Different variants of the DO{sub 22} superlattice can coexist in the matrix, and the interface between precipitate and the matrix remain coherence at the atomic scale. The three dimensional form of the DO{sub 22} precipitates constructed from three mutually perpendicular projections is an ellipsoidal stick, and the directions of elongations are along the longest axis of the unit cell for DO{sub 22} phase. - Highlights: •The DO{sub 22} phase precipitated in the Ni-Cr-W alloy has a high thermal stability. •The morphology of DO{sub 22} superlattice has been determined to be ellipsoid. •The interface between DO{sub 22} phase and matrix are fully coherent at the atomic scale. •Different variants of DO{sub 22} phase occur equiprobably. •The alloy strength can be improved dramatically by the nanoscale DO{sub 22} particles.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Quantitative measurement for the microstructural parameters of nano-precipitates in Al-Mg-Si-Cu alloys

Size, number density and volume fraction of nano-precipitates are important microstructural parameters controlling the strengthening of materials. In this work a widely accessible, convenient, moderately time efficient method with acceptable accuracy and precision has been provided for measurement of volume fraction of nano-precipitates in crystalline materials. The method is based on the traditional but highly accurate technique of measuring foil thickness via convergent beam electron diffraction. A new equation is proposed and verified with the aid of 3-dimensional atom probe (3DAP) analysis, to compensate for the additional error resulted from the hardly distinguishable contrast of too short incomplete precipitates cut by the foil surface. The method can be performed on a regular foil specimen with a modern LaB{sub 6} or field-emission-gun transmission electron microscope. Precisions around ± 16% have been obtained for precipitate volume fractions of needle-like β″/C and Q precipitates in an aged Al-Mg-Si-Cu alloy. The measured number density is close to that directly obtained using 3DAP analysis by a misfit of 4.5%, and the estimated precision for number density measurement is about ± 11%. The limitations of the method are also discussed. - Highlights: •A facile method for measuring volume fraction of nano-precipitates based on CBED •An equation to compensate for small invisible precipitates, with 3DAP verification •Precisions around ± 16% for volume fraction and ± 11% for number density.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Precipitation behavior of L12 Al3Zr phase in Al-Mg-Zr alloy

Highlights: • Precipitation behavior of the as-cast Al-3.0Mg-0.25Zr alloy was studied. • Discontinuous and continuous precipitation mechanisms of Al{sub 3}Zr phase are observed. • Precipitation type changes from discontinuous to continuous at two-step annealing. • Developed treatment mode provides high dispersoids dense and maximum aging effect. - Abstract: Increasing the recrystallization resistance and the mechanical properties of aluminum-based alloys is possible due to the formation of a nanoscale L1{sub 2}-structured Al{sub 3}Zr phase. Treatment conditions and alloys composition affect the size and density of dispersoids and their final properties. In this work we analyze the decomposition of the supersaturated solid solution in the as-cast Al-3%Mg-0.25%Zr alloy for different annealing modes to understand the precipitation kinetics of the Al{sub 3}Zr phase in the presence of Mg. We found that both discontinuous and continuous precipitation mechanisms of the Al{sub 3}Zr phase are possible in the studied low-alloyed material. One-step annealing leads to the formation of coarse (17 nm) spherical precipitates of a coherent L1{sub 2}-structured Al{sub 3}Zr phase and discontinuously formed fan-shaped aggregations of the same phase. Two-step annealing provided for the maximum precipitation hardening with the formation of high-density nanoscale (7 nm) dispersoids of the Al{sub 3}Zr phase. This study highlights the importance of the annealing mode of the as-cast material for achieving a high density of the fine L1{sub 2} structured Al{sub 3}Zr phase and the maximum hardening effect.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Morphology evolution of γ′ precipitates in a powder metallurgy Ni-base superalloy

Highlights: • The 3-D morphology of the γ′ precipitate for the Ni-base superalloy was characterized using the electronic etching. • Various morphologies of the γ′ precipitates, including cuboids, octet and dendritic shape, were observed. • Cooling rate has a significant influence on the morphology of the γ′ precipitate. • When the cooling rate was lower than 6 °C/min, the dendritic shape γ′ with eight-primary-branch pattern was observed. - Abstract: Effect of the cooling rate on the morphological evolution of the γ′ precipitate in a powder metallurgy Ni-base superalloy FGH96 was studied. Results showed that as the cooling rate decreased from 600 °C/min to 2 °C/min, the precipitate morphology transformed from sphere to cuboid, octet and dendrite. As the cooling rate increased, the mean size of the γ′ precipitates decreased while the nucleation density increased. When the cooling rate was lower than 6 °C/min, the precipitate would evolve from a sphere to cuboids with concave faces, octets, dendrite to final split-off branches. The morphological transition was driven by energy balance between coherent strain induced by the γ′/γ lattice misfit and interface energy. The dendritic shape γ′ exhibited an eight-primary-branch pattern with preferred growth direction along <111>, and secondary arms along <100>.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Controlling the MC and M2C carbide precipitation in Ferrium® M54® steel to achieve optimum ultimate tensile strength/fracture toughness balance

Highlights: • Small and uniformly distributed undissolved Ti-rich MC carbides control the grain size during the austenitization • High austenitizing temperature (1060°C) allows the full dissolution of the coarse carbides (size > several of 100nm) • Intensive nanometer-sized carbides precipitate during tempering thanks to the high supersaturation of alloying elements • Coarse carbides dissolution and nanometer-size carbides precipitation is necessary to achieve high UTS/K{sub I}C balance - Abstract: Ferrium® M54® exhibits an excellent UTS/K{sub 1C} balance allowing its application in aeronautical structures. This steel belongs to the Co-Ni UHS steels family with M{sub 2}C nanometer-size carbide precipitation during tempering. These steels provide very high strength with a very good fracture toughness thanks to the M{sub 2}C fine precipitation during tempering, but also because coarse particles are dissolved during austenitizing without grain coarsening. The goal of this article is to identify the different carbide populations in M54®. A small addition of Ti in M54® forms a Ti-rich MC carbide precipitation that is stable at high temperature. Consequently, during austenitization at 1060 °C, all other types of coarse carbides are dissolved in the matrix without grain coarsening. As a very small part of the initial carbon content is needed to form MC carbides, efficient and intensive nanometric M{sub 2}C carbide precipitation takes place during tempering, leading to very high final strength. Due to this double precipitation of carbides in M54®, the steel achieves an outstanding UTS/K{sub 1C} balance.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Investigation of structure, morphology and orientation of precipitates in Mg−Bi alloy

Highlights: • Rod-shaped, cuboid-shaped and polyhedral α-Mg{sub 3}Bi{sub 2} are found in MgBi alloy. • The two orientation relationships between Mg{sub 3}Bi{sub 2} and Mg matrix are confirmed. • Growth of rod-shaped Mg{sub 3}Bi{sub 2} is fast along 〈10 1-bar 0〉 direction of precipitate. • Interfacial matching between polyhedral Mg{sub 3}Bi{sub 2} and Mg matrix is the best. - Abstract: In Mg−0.8 at.% Bi binary alloys,the structure, the morphology and the orientation of precipitates were characterized by high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark detector field scanning transmission electron microscopy (HAADF−STEM) techniques. The main precipitate is the α-Mg{sub 3}Bi{sub 2} phase with hexagonal structure (P 3-bar m1). The morphology of α-Mg{sub 3}Bi{sub 2} precipitate is classified into three types, rod-shaped, cuboid-shaped and polyhedral, which are related closely with orientation relationships (ORs) between α-Mg{sub 3}Bi{sub 2} precipitate and αMg matrix. For the first two types of morphologies, precipitate and αMg matrix can maintain the following ORs: [11 2-bar 0]{sub Mg{sub 3Bi{sub 2}}}//[0001]{sub Mg} and (1 1-bar 00){sub Mg{sub 3Bi{sub 2}}}//(1 1-bar 00){sub Mg}. In contrast, another set of ORs between polyhedral α-Mg{sub 3}Bi{sub 2} and αMg matrix can be determined as: [11 2-bar 0]{sub Mg{sub 3Bi{sub 2}}}//[11 2-bar 0]{sub Mg} and (0003){sub Mg{sub 3Bi{sub 2}}}//(1 1-bar 01){sub Mg}. The morphology of α-Mg{sub 3}Bi{sub 2} precipitates is discussed particularly based on the interfacial misfit mechanism.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Effect of annealing after strip casting on microstructure, precipitates and texture in non-oriented silicon steel produced by twin-roll strip casting

Highlights: • Non-oriented silicon steel with superior magnetic properties was produced by twin-roll strip casting. • The effect of annealing after strip casting on microstructure, precipitates and texture was investigated. • Role of precipitates in microstructure and texture evolution along the entire route was explored. • High magnetic induction and strong λ-fiber texture was obtained by optimizing strip annealing process. - Abstract: A 3.1 mm thick non-oriented Fe-1.0% Si steel as-cast strip was produced by twin-roll strip casting. Samples with/without strip annealing were cold rolled to 0.5 mm and then annealed. The development of microstructure, precipitate and texture was characterized along the entire processing route. It was found that annealing after strip casting had a minor influence on the average grain size and texture of the as-cast strip. A large number of particles precipitated and coarsened during the strip annealing process. Meanwhile, precipitates hindered dislocation slip and crystal rotation such that more significant in-grain shear bands were formed in cold rolled sheets. During recrystallization annealing process, the newly formed fine precipitates in directly cold-rolled sheets consumed stored strain energy and also hindered grain growth. But the initial precipitates in the annealed strip grew further and the effect of pinning of dislocations and grain boundary was lost. Therefore, annealed sheets with strip annealing process showed homogeneous equiaxed grains and the recrystallization texture was characterized by strong λ-fiber texture, which led to high permeability.

36 MATERIALS SCIENCE↗

DOE OSTI2011

Influence of the precipitation pH on the compositions and properties of Bi-based oxyiodide photocatalysts

Graphical abstract: A series of Bi-based oxyiodide photocatalysts with different compositions were synthesized via a precipitation-filtration process followed by hydrothermal treatment. The effects of the precipitation pH values on the compositions and photocatalytic activities of the bismuth oxyiodides were investigated. Research highlights: {yields} BiOI, Bi{sub 4}O{sub 5}I{sub 2}, Bi{sub 7}O{sub 9}I{sub 3} and Bi{sub 5}O{sub 7}I were obtained via a precipitation-filtration process followed by hydrothermal treatment. {yields} The compositions of the bismuth oxyiodides could be controlled by adjusting the precipitation pH values. {yields} All the bismuth oxyiodides exhibit photocatalytic activity on decomposing methyl orange. -- Abstract: A series of Bi-based oxyiodide photocatalysts with different compositions were synthesized via a precipitation-filtration process followed by hydrothermal treatment. The compositions of the bismuth oxyiodides could be controlled by adjusting the precipitation pH values. The effects of the precipitation pH values on the compositions and photocatalytic activities of the bismuth oxyiodides were investigated and the relationship between structure and photocatalytic property is discussed. All the as-prepared powders exhibit photocatalytic activity on decomposing methyl orange under visible light irradiation. The activity increases with increasing content of iodine in the bismuth oxyiodides.

36 MATERIALS SCIENCE↗

DOE OSTI2018

High-temperature strengthening mechanisms of Laves and B2 precipitates in a novel ferritic alloy

Precipitates of the Laves and B2 phases were engineered in a newly-designed advanced ferritic alloy. Under creep test at 650 °C with 120 MPa, the material showed a steady-state minimum creep rate of 1 × 10 –4 h –1 , about one order of magnitude lower than T91. Microstructural characterization of the ferritic alloy revealed primarily ductile and partially brittle fractures after the creep test. Coarse Laves phase (~ 1 µm) was observed associating with the brittle fracture, resulting in reduced creep ductility. However, fine Laves phase precipitates (~ 100 nm) helped the dimple-ductile fracture and strengthened the material through impeding the motion of dislocations and boundaries. Unlike the B2 precipitates remained coherent exerting the classic Orowan bypassing mechanism at the brittle location, some of the B2 precipitates at the ductile location became incoherent and can develop an attractive interaction with dislocations. In conclusion, this coherency change of B2 precipitates, together with the nucleation of ultrafine (~ 40 nm) Laves phase precipitates during the creep test, would compensate for the coarsening-induced loss of Orowan strengthening of coherent B2 precipitates.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Role of Fe in long-range ordered Ni 2 Cr precipitates in Ni-Cr-Fe model alloys during isothermal aging

The precipitation of new phases during long-term service at elevated temperatures is a concern for the thermal stability of engineering alloys. In Ni-Cr-based alloys, e.g., Alloy 690, the formation of long-range ordered Ni 2 Cr causes embrittlement and may impact the lifetime of nuclear power plant components. In this work, we quantify the formation and evolution of Ni 2 Cr precipitation in eleven Ni-Cr-Fe model alloys with 0, 5, 7, and 10wt % Fe contents, and with Ni/Cr atomic ratios of 1.8, 2.0, 2.2, 2.4. These alloys were isothermally aged up to 10,000h at temperatures between 330 and 475°C. The alloys were characterized by synchrotron-based x-ray diffraction and Vickers hardness testing to quantify Ni 2 Cr precipitate size, and the impact of precipitate size on the mechanical properties as a function of Fe content. After 10,000 h of aging at 475°C and 418°C, the formation of Ni 2 Cr was observed in all alloys with 0 and 5wt % Fe. After 10,000h of aging at 418°C, Ni 2 Cr precipitates were also observed in the 7wt % Fe containing Ni/Cr=2.0 sample. Further, no clear evidence of Ni 2 Cr was observed in any of the 10wt % Fe samples at any time and temperature combination. We find that the face-centered cubic matrix lattice contraction and Vickers hardness are correlated with the Ni 2 Cr formation. The greatest change in hardness and lattice contraction occurs in stoichiometric alloys (Ni/Cr=2.0) with 0wt % Fe at 475°C. The rate of change in the material properties for the 5wt % Fe alloys is reduced, however the magnitude of changes is similar to 0wt % Fe alloys. A precipitation hardening model developed for Ni-Cr alloys based on critical resolved shear stress with weakly coupled dislocations shows a clear link between Ni 2 Cr precipitate size and hardness. This trend held across all alloys with Ni 2 Cr formation regardless of Fe concentration. This important structure-property relationship can potentially help define Ni-Cr-Fe-based component lifetimes directly through an understanding of how Ni 2 Cr formation impacts mechanical properties as a function of Fe content.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Ion-Specific Precipitation of Extractants Enables Rare-Earth Separation and Wastewater Remediation from Solvent Extraction of Critical Elements

The increasing demand for rare-earth elements (REEs) necessitates sustainable recovery strategies, particularly from secondary sources, such as electronic waste. Solvent extraction is the primary industrial method for REE separation; however, the unintentional dissolution of extractants into wastewater poses serious environmental risks, leading to organic contamination and process inefficiencies. Existing wastewater treatment methods struggle to remove these persistent pollutants, underscoring the need for innovative recovery approaches. Herein, we present a ligand-mediated precipitation strategy that simultaneously recovers REEs and removes dissolved extractants from solvent extraction wastewater. We show that residual extractants in the aqueous phase can selectively bind REEs, inducing their precipitation while leaving transition metals in solution. By integrating FTIR spectroscopy, EDS, XPS, EXAFS, and SAXS, we elucidate the mechanism of ion-specific precipitation and the local coordination environment of metal ions in the precipitate. Importantly, we demonstrate that the precipitated extractants can be efficiently recovered and reused, providing a closed-loop solution that enhances sustainability. Applying this method to leachates from samarium–cobalt (Sm–Co) and neodymium–iron–boron (NdFeB) mixed magnets, we achieve highly selective REE precipitation under mild conditions, demonstrating a scalable and cost-effective pathway for REE recovery, wastewater purification, and extractant recycling. In conclusion, by integrating element-specific ligand-mediated precipitation with extractant reuse, this work offers a transformative approach to REE separation that reduces the environmental impact while improving resource efficiency.

E-waste↗

DOE OSTI2016

Impact of mineral precipitation on flow and mixing in porous media determined by microcomputed tomography and MRI

Here, precipitation reactions in porous media influence transport properties of the environment and can control advective and dispersive transport. In subsurface environments, mixing of saline groundwater or injected solutions for remediation with fresh groundwater can induce supersaturation of constituents and drive precipitation reactions. Magnetic resonance imaging (MRI) and micro-computed tomography (µ-CT) were employed as complimentary techniques to evaluate advection, dispersion and formation of precipitate in a 3D porous media flow cell. Two parallel fluids were flowed concentrically through the porous media under two flow rate conditions with Na 2 CO 3 and CaCl 2 in the inner and outer fluids, respectively. Upon mixing, calcium carbonate became supersaturated and formed a precipitate at the interface of the two fluids. Spatial maps of changing local velocity fields and dispersion in the flow cell were generated from MRI, while high resolution imaging of the precipitate formed in the porous media was achieved via µ-CT imaging. Formation of a precipitate layer minimized dispersive and advective transport between the two fluids and the shape of the precipitation was influenced by the flow rate condition.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2011

Intensity, duration, and frequency of precipitation extremes under 21st-century warming scenarios

Recent research on the projection of precipitation extremes has either focused on conceptual physical mechanisms that generate heavy precipitation or rigorous statistical methods that extrapolate tail behavior. However, informing both climate prediction and impact assessment requires concurrent physically and statistically oriented analysis. A combined examination of climate model simulations and observation-based reanalysis data sets suggests more intense and frequent precipitation extremes under 21st-century warming scenarios. Utilization of statistical extreme value theory and resampling-based uncertainty quantification combined with consideration of the Clausius-Clapeyron relationship reveals consistently intensifying trends for precipitation extremes at a global-average scale. However, regional and decadal analyses reveal specific discrepancies in the physical mechanisms governing precipitation extremes, as well as their statistical trends, especially in the tropics. The intensifying trend of precipitation extremes has quantifiable impacts on intensity-duration-frequency curves, which in turn have direct implications for hydraulic engineering design and water-resources management. The larger uncertainties at regional and decadal scales suggest the need for caution during regional-scale adaptation or preparedness decisions. Future research needs to explore the possibility of uncertainty reduction through higher resolution global climate models, statistical or dynamical downscaling, as well as improved understanding of precipitation extremes processes.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2019

Nonlinear Response of Extreme Precipitation to Warming in CESM1

The response of extreme precipitation to warming varies widely among climate models, especially in the tropics. In some models, there have been indications that the rate of response increases with warming – that the response is not linear. In this work, we investigate the evolution of extreme precipitation, quantified by the maximum accumulated precipitation in a day each year, in CESM1. We find that tropical- and global-average extreme precipitation are related to global mean surface temperature quadratically. This behavior is associated with an increase in the large scale fraction of extreme precipitation, and also strengthening circulation on extreme 25 precipitation days. Compared to other CMIP5 models, the nonlinearity in CESM1 is among the largest. One implication is that the difference between CESM1 simulations with full forcing and with fixed aerosols cannot be used to isolate the response of extreme precipitation to aerosols, as the resulting climates are not equally warm.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2022

Impacts of Large-Scale Urbanization and Irrigation on Summer Precipitation in the Mid-Atlantic Region of the United States

This study investigates how urbanization and irrigation in the United States east of the Rocky Mountains affect summer precipitation in the Mid-Atlantic region (MAR) using convection-permitting Weather Research and Forecasting model simulations with/without urbanization or irrigation. In this work, a feature tracking algorithm is used to identify precipitation from mesoscale convective systems (MCSs), isolated deep convection (IDC), and non-convective systems (NC). Overall, urbanization suppresses all three types of precipitation in the MAR by reducing water vapor content and convective available potential energy, while irrigation enhances IDC and NC precipitation but suppresses MCS precipitation. Examination of the MCS and IDC initiation locations indicates that irrigation suppresses MAR precipitation that is produced by MCSs initiated in the Great Plains and Midwest (GP) but enhances MAR precipitation from MCSs initiated locally within the region. Irrigation induces a mid-level cyclonic circulation anomaly centering in the Southeast, hindering the eastward propagation and development of MCSs from the GP.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2023

Southern Ocean Low Cloud and Precipitation Phase Observed During the Macquarie Island Cloud and Radiation Experiment (MICRE)

Shallow cloud decks residing in or near the boundary layer cover a large fraction of the Southern Ocean (SO) and play a major role in determining the amount of shortwave radiation reflected back to space from this region. In this article, we examine the macrophysical characteristics and thermodynamic phase of low clouds (tops <3 km) and precipitation using ground-based ceilometer, depolarization lidar and vertically-pointing W-band radar measurements collected during the Macquarie Island Cloud and Radiation Experiment (MICRE) from April 2016 to March 2017. During MICRE, low clouds occurred ~65% of the time on average (slightly more often in austral winter than summer). About 2/3 of low clouds were cold-topped (temperatures ≤0°C). These were thicker and had higher bases on average than warm-topped clouds. 83%–88% of cold-topped low clouds were liquid phase at cloud base (depending on the season). The majority of low clouds had precipitation in the vertical range 150–250 m below cloud base, a significant fraction of which did not reach the surface. Phase characterization is limited to the period between April 2016 and November 2016. Small-particle (low-radar-reflectivity) precipitation (which dominates precipitation occurrence) was mostly liquid below-cloud, while large-particle precipitation (which dominates total accumulation) was predominantly mixed/ambiguous or ice phase. Approximately 40% of cold-topped clouds had mixed/ambiguous or ice phase precipitation below (with predominantly liquid phase cloud droplets at cloud base). Below-cloud precipitation with radar reflectivity factors below about -10 dBZ were predominantly liquid, while reflectivity factors above about 0 dBZ were predominantly ice.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2015

Kinetics modeling of precipitation with characteristic shape during post-implantation annealing

In this study, we investigated the precipitation with characteristic shape in the microstructure during post-implantation annealing via a theoretical modeling approach. The processes of precipitates formation and evolution during phase separation were based on a nucleation and growth mechanism of atomic diffusion. Different stages of the precipitation, including the nucleation, growth and coalescence, were distinctly revealed in the numerical simulations. In addition, the influences of ion dose, temperature and crystallographic symmetry on the processes of faceted precipitation were also demonstrated. To comprehend the kinetic mechanism, the simulation results were further analyzed quantitatively by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The Avrami exponents obtained from the regression curves varied from 1.47 to 0.52 for different conditions. With the increase of ion dose and temperature, the nucleation and growth of precipitations were expedited in accordance with the shortened incubation time and the raised coefficient of growth rate. A miscellaneous shape of precipitates in various crystallographic symmetry systems could be simulated through this anisotropic model. From the analyses of the kinetics, more fundamental information about the nucleation and growth mechanism of faceted precipitation during post-implantation annealing was acquired for future application.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Metastable precipitation and ion–extractant transport in liquid–liquid separations of trivalent elements

The extractant-assisted transport of metal ions from aqueous to organic environments by liquid–liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion–extractant precipitates away from the liquid–liquid interface, separated from it by a depletion region without precipitates. Although the precipitate is soluble in the organic phase, the depletion region separates the two and ions are sequestered in a long-lived metastable state. Since precipitation removes extractants from the aqueous phase, even extractants that are sparingly soluble in water will continue to be withdrawn from the organic phase to feed the aqueous precipitation process. Solute concentrations in both phases and the aqueous pH influence the temporal evolution of the process and ionic partitioning between the precipitate and organic phase. Aqueous ion–extractant precipitation during liquid–liquid extraction provides a reaction path that can influence the extraction kinetics, which plays an important role in designing advanced processes to separate rare earths and other minerals.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗