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Structure of the Bastnäsite (001) Surface by Crystal Truncation Rod X-ray Diffraction and Ab Initio Molecular Dynamics: Implications for Separations of a Rare Earth Ore Mineral
Bastnäsite ((Ce,La)FCO 3 ) is the primary mineral source of light rare earth elements, but its surface structure is not well understood. This presents a major challenge in improving beneficiation strategies. In this work, a synergistic combination of X-ray scattering and ab initio molecular dynamics (AIMD) was used to gain atomistic insight into the interfacial structure of bastnäsite. Surface X-ray scattering was used to measure crystal truncation rods (CTRs) of the bastnäsite (001) surface, a significant crystal face with a previously unknown termination. The best-fit atomic-scale model of the CTR data features a carbonate layer at the surface, which is stabilized by the relaxation of carbonate groups from their bulk structural positions. AIMD simulations predict similar surface relaxations, which are shown to be influenced by the protonation of oxygen atoms at the surface. Evidence of ordered water at the interface is also observed in the best-fit model and AIMD simulations. Further, the presence of a carbonate layer at this dominant crystal surface is significant for improving separation technologies because most commonly used ligands utilize anionic functional groups to chelate metal cations at particle surfaces. Without modification, anionic ligands are expected to have poor affinity for the carbonate-terminated (001) surface.
Molecular Recognition at Mineral Interfaces: Implications for the Beneficiation of Rare Earth Ores
Ce-bastnäsite is the single largest mineral source for light rare-earth elements. In view of the growing industrial importance of rare-earth minerals, it is critical to develop more efficient methods for separating the valuable rare-earth-containing minerals from the surrounding gangue. In this work, we employ a combination of periodic density functional theory (DFT) and molecular mechanics (MM) calculations together with the de novo molecular design program HostDesigner to identify bis-phosphinate ligands that preferentially bind to the (100) Ce-bastnäsite surface rather than the (104) calcite surface. DFT calculations for a simple phosphinate ligand were employed to qualitatively understand key behaviors involved in ligand–metal, ligand–solvent, and solvent–metal interactions. These insights were then used to guide the search for flexible, rigid, and semirigid hydrocarbon linkers to identify candidate bis-phosphinate ligands with the potential to bind preferentially to Ce-bastnäsite. Among the five most promising bis-phosphinate ligands suggested by theoretical studies, three ligands were synthesized and their adsorption characteristics to bastnäsite (100) interfaces were characterized using vibrational sum-frequency (vSFG) spectroscopy, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, and isothermal titration calorimetry (ITC). The efficacy of the selective interfacial molecular binding was demonstrated by identifying a bis-phosphinate ligand capable of providing an overall higher surface coverage of alkyl groups relative to a monophosphinate ligand. The results highlight the interplay between adsorption binding strength and maximum surface coverage in determining ligand efficiency to render the mineral surface hydrophobic. DFT calculations further indicate that all tested ligands have higher affinity for Ce-bastnäsite than for calcite. Finally, this is consistent with the ITC data showing stronger adsorption enthalpy to bastnäsite than to calcite, making these ligands promising candidates for selective flotation of Ce-bastnäsite.
Oxygen Isotope and Fluorine Impurity Signatures during the Conversion of Uranium Ore Concentrates to Nuclear Fuel
Not Available
Direct extraction of lithium from ores by electrochemical leaching
With the rapid increase in lithium consumption for electric vehicle applications, its price soared during the past decade. To secure a reliable and cost-effective supply chain, it is critical to unlock alternative lithium extraction resources beyond conventional brine. In this study, we develop an electrochemical method to directly leach lithium from α-phase spodumene. We find the H 2 O 2 promoter can significantly reduce the leaching potential by facilitating the electron transfer and changing the reaction path. Upon leaching, β-phase spodumene shows a typical phase transformation to HAlSi 2 O 6 , while leached α-phase remains its original crystal phase with a lattice shrinkage. To demonstrate the scale-up potential of electrochemical leaching, we design a catalyst-modified high-throughput current collector for high loading of suspended spodumene, achieving a leaching current of 18 mA and a leaching efficiency of 92.2%. Electrochemical leaching will revolutionize traditional leaching and recycling processes by minimizing the environmental footprint and energy consumption.
Activating magnetite ores for aqueous ironmaking at high current densities
Low-temperature electrochemical cells reducing iron oxides to metal in alkaline electrolytes can support fully electrified steelmaking processes. Previous studies on these cells have primarily focused on high-surface-area hematite, Fe 2 O 3 , reactants whereas attempts to reduce suspensions of magnetite, Fe 3 O 4 —one of the two feedstocks for existing ironmaking reactors—have generally been limited to low rates of reaction (<30 mA cm −2 ). Here, in this study, we control the crystalline domain size of Fe 2 O 3 and Fe 3 O 4 particles in 10 M NaOH electrolytes to study how the nanoscale morphology of oxides controls the rate of electrochemical ironmaking. Rotating-ring disk electrode measurements of Fe 2+ , in situ Raman spectroscopy of the electrode surface, and ex situ electron microscopy were consistent with a hypothesized passivation process at Fe 3 O 4 surfaces that may prevent the continuous formation of soluble intermediates. Sufficiently small (<100 nm diameter) oxide particles yielded Fe partial current densities >160 mA cm −2 , a fivefold increase relative to previously reported rates for Fe 3 O 4 suspensions and comparable to active Fe 2 O 3 . Electron microscopy revealed that electrodeposited films were composed of micron-scale crystalline Fe domains with a porous film of Fe 3 O 4 nanoparticles and supports a model where Fe is grown primarily from soluble Fe 2+ intermediates. Based on these insights, inactive blast-furnace-grade iron-oxides were transformed into high surface area nanoparticles (1.6 to 229.2 m 2 g −1 ) via reprecipitation, leading to a ninefold enhancement in faradaic efficiency and an Fe partial current density of 120 mA cm −2 . When integrated with chlor-iron cells producing reagents for reprecipitation, this approach could lead to a cost-competitive process for electrochemical ironmaking from industrially relevant feedstocks.
Synthesis and characterization of highly purified nanosilica from pyrophyllite ores
A simple method based on alkaline extraction followed by acid precipitation and acid dissolution has been developed to produce highly purified nanosilica from pyrophyllite materials. The reaction parameters such as molar ratio NaOH/SiO{sub 2}, reaction time and reaction temperature are varied for obtaining maximum nanosilica convertion. About 99,45% highly purified precipitated nanosilica measure with ICP, 259 m{sup 2}/gr measure with BET surface area, 97% whiteness and 3 ml/gr oil absorbtion from pyrophyllite materials has been achieved in closed system at 150°C within 180 min. The physicals and chemical properties (such as X-Ray Diffraction from PANalytical, X-Ray Fluorescence Minipal4 from PANanalytical, BET surface area, Forier Transform Infra Red Spectroscopy from Hitachi, and SEM-EDS Inspect-S50 from FEI Company) of the highly purity nanosilica were studied.
Application of Visible/Near-Infrared Reflectance Spectroscopy to Uranium Ore Concentrates for Nuclear Forensic Analysis and Attribution
Abstract not provided
Mobilization and agglomeration of uraninite nanoparticles: A nano-mineralogical study of samples from the Matoush Uranium ore deposit
Not provided.
First-principles simulation of solvation structure and deprotonation reactions of ore forming metal ions in very nonideal solutions
Advances in algorithms and computational performance achieved in this grant period have allowed the atomic level dynamical simulation of complex nanoscale materials using interparticle forces calculated directly from an accurate density functional solution to the electronic Schrödinger equation (ab-initio molecular dynamics, AIMD). Focus of this program was on the prediction and analysis of the properties of environmentally important ions in aqueous solutions. AIMD methods have provided chemical interpretations of these very complex systems with an unprecedented level of accuracy and detail. The structure of the solvation region neighboring a highly charged metal ion (e.g., 3+) in an aqueous solution is very different from that of bulk water. The many-body behaviors (polarization, charge transfer, etc.) of the ion-water and water-water interactions in this region are difficult to capture with conventional empirical potentials. However, a large numbers of waters (up to 128 waters) are required to fully describe chemical events in the extended hydrations shells and long simulation times are needed to reliably sample the system. Taken together this makes simulation at the 1 st principles level a very large computational problem. Our AIMD simulation results using these methods agree with the measured octahedral structure of the 1 st solvation shell of Al 3+ at the 1 st shell boundary and a calculated radius of 1.937 (exp. 1.9). Our calculated average 2 nd shell radius agrees remarkably well with the measured radius, 4.093 Å calculated vs. the measured value of 4.0-4.15 Å.
The Application of Current Mineral Processing and Extractive Metallurgy Technologies to Potential Rare Earth Ores in the U.S. Coal Measures: Near-Term Opportunities to Fill Out the U.S. Value Chain
This report will consider the potential for currently available mineral processing and extractive metallurgy technologies to produce separated rare earth compounds from U.S. coal and coal byproducts. Implementation of production as such would require restoration of elements of the rare earth value chain that have recently been absent in the U.S., notably for chemical extraction of rare earth compounds from the mineral form (i.e. hydrometallurgical extraction). A variety of existing technologies are available for use in both mineral processing and extractive metallurgy applied to RE production in the U.S. As will be discussed, once a mineral concentrate is produced, the contained rare earth value can be large compared with transportation costs, and the sections of the value chain dealing with chemical extraction (the largest cost) and separation into individual rare earth compounds can be remotely located. Also, as will be discussed, this has been the rule rather than exception in the history of the rare earth industry in the U.S. A strategy, possibly to include repurposing of existing metallurgical processing facilities, will be presented for near-term production, using a decentralized set of facilities. Also presented will be research results from the Office of Fossil Energy (FE) and the National Energy Technology Laboratory (NETL), within the U.S. Department of Energy, relevant to economic feasibility of rare earth production, notably from the standpoint of establishing which materials are capable of providing economic production. Simple methodologies are presented for both establishment of cutoff grades and economic evaluation of a process. The goal of this report is to present an overview of methods and pathways that will result in “the achievement of near-term rare earth production, using currently available technologies to produce a mixed, chemical extracted rare earth concentrate, and existing and new facilities to produce separated rare earths that can “plug in” to the metals and magnet production facilities.” A set of recommendations appears at the end of this work, involving both research and project development activities which will enable the achievement of this noble goal. A set of recommendations appears at the end of this work, involving both research and project development activities.
Selective hydrothermal extraction of lanthanides: Mimicking natural ore-forming processes [Slides]
Rare Earth Elements (REE) consumption in the US was 20,000 metric ton in 2018. China controls 97% of the global REE market. The aims for new technology are to 1. Avoid investing in extraction of cheap LREE, extract M/HREE only → increase the value of the intermediate/final product, 2. Exclude extraction and concentration of U and Th → avoid investment in rad remediation, and 3. Maximize environmental friendliness of the technology. Hints from nature can aid in achieving these amis.
Utility of Sr and Nd isotope signatures in U ores and UOCs [Slides]
Abstract not provided.