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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on MnCuSe4 by Materials Project

MnCuSe4 is pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Mn7+ is bonded to six Se2- atoms to form MnSe6 octahedra that share corners with four equivalent MnSe6 octahedra and corners with eight equivalent CuSe6 octahedra. The corner-sharing octahedra tilt angles range from 64–65°. There are a spread of Mn–Se bond distances ranging from 2.58–2.64 Å. Cu1+ is bonded to six Se2- atoms to form CuSe6 octahedra that share corners with four equivalent CuSe6 octahedra and corners with eight equivalent MnSe6 octahedra. The corner-sharing octahedra tilt angles range from 64–65°. There are a spread of Cu–Se bond distances ranging from 2.59–2.63 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent Mn7+, one Cu1+, and one Se2- atom. The Se–Se bond length is 2.43 Å. In the second Se2- site, Se2- is bonded in a 4-coordinate geometry to one Mn7+, two equivalent Cu1+, and one Se2- atom. The Se–Se bond length is 2.42 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiSeS by Materials Project

NiSSe is Pyrite-derived structured and crystallizes in the cubic P2_13 space group. The structure is three-dimensional. Ni4+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form NiSe3S3 octahedra that share corners with twelve equivalent NiSe3S3 octahedra, corners with three equivalent SeNi3S tetrahedra, and corners with three equivalent SNi3Se tetrahedra. The corner-sharing octahedral tilt angles are 64°. All Ni–Se bond lengths are 2.47 Å. All Ni–S bond lengths are 2.37 Å. Se2- is bonded to three equivalent Ni4+ and one S2- atom to form distorted SeNi3S tetrahedra that share corners with three equivalent NiSe3S3 octahedra, corners with six equivalent SeNi3S tetrahedra, and corners with nine equivalent SNi3Se tetrahedra. The corner-sharing octahedral tilt angles are 78°. The Se–S bond length is 2.32 Å. S2- is bonded to three equivalent Ni4+ and one Se2- atom to form distorted SNi3Se tetrahedra that share corners with three equivalent NiSe3S3 octahedra, corners with six equivalent SNi3Se tetrahedra, and corners with nine equivalent SeNi3S tetrahedra. The corner-sharing octahedral tilt angles are 78°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Li4NbCr(TeO6)2 by Materials Project

Li4NbCr(TeO6)2 is pyrite-derived structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Li–O bond distances ranging from 1.94–2.51 Å. In the second Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Li–O bond distances ranging from 1.95–2.47 Å. In the third Li1+ site, Li1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Li–O bond distances ranging from 1.99–2.33 Å. In the fourth Li1+ site, Li1+ is bonded in a distorted trigonal planar geometry to three O2- atoms. There are a spread of Li–O bond distances ranging from 1.93–2.00 Å. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six TeO6 octahedra. The corner-sharing octahedra tilt angles range from 37–42°. There are a spread of Nb–O bond distances ranging from 1.95–2.06 Å. Cr5+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six TeO6 octahedra. The corner-sharing octahedra tilt angles range from 36–39°. There are a spread of Cr–O bond distances ranging from 2.00–2.07 Å. There are two inequivalent Te5+ sites. In the first Te5+ site, Te5+ is bonded to six O2- atoms to form TeO6 octahedra that share corners with two equivalent CrO6 octahedra and corners with four equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 38–42°. There are a spread of Te–O bond distances ranging from 1.91–2.00 Å. In the second Te5+ site, Te5+ is bonded to six O2- atoms to form TeO6 octahedra that share corners with two equivalent NbO6 octahedra and corners with four equivalent CrO6 octahedra. The corner-sharing octahedra tilt angles range from 36–39°. There are a spread of Te–O bond distances ranging from 1.92–2.01 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Li1+, one Nb5+, and one Te5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Li1+, one Cr5+, and one Te5+ atom. In the third O2- site, O2- is bonded to two Li1+, one Cr5+, and one Te5+ atom to form distorted corner-sharing OLi2CrTe tetrahedra. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Li1+, one Nb5+, and one Te5+ atom. In the fifth O2- site, O2- is bonded in a distorted see-saw-like geometry to two Li1+, one Cr5+, and one Te5+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two Li1+, one Nb5+, and one Te5+ atom. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to one Li1+, one Nb5+, and one Te5+ atom. In the eighth O2- site, O2- is bonded to two Li1+, one Cr5+, and one Te5+ atom to form a mixture of distorted corner and edge-sharing OLi2CrTe tetrahedra. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to two Li1+, one Nb5+, and one Te5+ atom. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two Li1+, one Cr5+, and one Te5+ atom. In the eleventh O2- site, O2- is bonded to two Li1+, one Cr5+, and one Te5+ atom to form a mixture of distorted corner and edge-sharing OLi2CrTe tetrahedra. In the twelfth O2- site, O2- is bonded in a 3-coordinate geometry to one Li1+, one Nb5+, and one Te5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZnSe2 by Materials Project

ZnSe2 is Pyrite structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. Zn2+ is bonded to six equivalent Se1- atoms to form ZnSe6 octahedra that share corners with twelve equivalent ZnSe6 octahedra and corners with six equivalent SeZn3Se tetrahedra. The corner-sharing octahedral tilt angles are 66°. All Zn–Se bond lengths are 2.68 Å. Se1- is bonded to three equivalent Zn2+ and one Se1- atom to form distorted SeZn3Se tetrahedra that share corners with three equivalent ZnSe6 octahedra and corners with fifteen equivalent SeZn3Se tetrahedra. The corner-sharing octahedral tilt angles are 76°. The Se–Se bond length is 2.40 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MnZnTe4 by Materials Project

MnZnTe4 is pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Mn4+ is bonded to six Te+1.50- atoms to form MnTe6 octahedra that share corners with four equivalent MnTe6 octahedra and corners with eight equivalent ZnTe6 octahedra. The corner-sharing octahedra tilt angles range from 63–65°. There are two shorter (2.84 Å) and four longer (2.86 Å) Mn–Te bond lengths. Zn2+ is bonded to six Te+1.50- atoms to form ZnTe6 octahedra that share corners with four equivalent ZnTe6 octahedra and corners with eight equivalent MnTe6 octahedra. The corner-sharing octahedra tilt angles range from 63–65°. All Zn–Te bond lengths are 2.89 Å. There are two inequivalent Te+1.50- sites. In the first Te+1.50- site, Te+1.50- is bonded in a 4-coordinate geometry to one Mn4+, two equivalent Zn2+, and one Te+1.50- atom. The Te–Te bond length is 2.80 Å. In the second Te+1.50- site, Te+1.50- is bonded in a 4-coordinate geometry to two equivalent Mn4+, one Zn2+, and one Te+1.50- atom. The Te–Te bond length is 2.84 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RuRhS4 by Materials Project

RuRhS4 is Pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Ru5+ is bonded to six S2- atoms to form RuS6 octahedra that share corners with four equivalent RuS6 octahedra, corners with eight equivalent RhS6 octahedra, and corners with six SRu2RhS tetrahedra. The corner-sharing octahedra tilt angles range from 63–65°. There are two shorter (2.35 Å) and four longer (2.37 Å) Ru–S bond lengths. Rh3+ is bonded to six S2- atoms to form RhS6 octahedra that share corners with four equivalent RhS6 octahedra, corners with eight equivalent RuS6 octahedra, and corners with six SRu2RhS tetrahedra. The corner-sharing octahedra tilt angles range from 64–66°. There are four shorter (2.40 Å) and two longer (2.41 Å) Rh–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Ru5+, one Rh3+, and one S2- atom to form distorted SRu2RhS tetrahedra that share a cornercorner with one RhS6 octahedra, corners with two equivalent RuS6 octahedra, and corners with fifteen SRu2RhS tetrahedra. The corner-sharing octahedra tilt angles range from 77–79°. The S–S bond length is 2.27 Å. In the second S2- site, S2- is bonded to one Ru5+, two equivalent Rh3+, and one S2- atom to form distorted SRuRh2S tetrahedra that share a cornercorner with one RuS6 octahedra, corners with two equivalent RhS6 octahedra, and corners with fifteen SRu2RhS tetrahedra. The corner-sharing octahedra tilt angles range from 76–79°. The S–S bond length is 2.27 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on FeCo3S8 by Materials Project

FeCo3S8 is Pyrite-derived structured and crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Fe2+ is bonded to six equivalent S1- atoms to form FeS6 octahedra that share corners with twelve equivalent CoS6 octahedra. The corner-sharing octahedral tilt angles are 64°. All Fe–S bond lengths are 2.27 Å. Co2+ is bonded to six S1- atoms to form CoS6 octahedra that share corners with four equivalent FeS6 octahedra, corners with eight equivalent CoS6 octahedra, and corners with two equivalent SCo3S tetrahedra. The corner-sharing octahedra tilt angles range from 64–66°. There are two shorter (2.30 Å) and four longer (2.31 Å) Co–S bond lengths. There are two inequivalent S1- sites. In the first S1- site, S1- is bonded in a 4-coordinate geometry to one Fe2+, two equivalent Co2+, and one S1- atom. The S–S bond length is 2.17 Å. In the second S1- site, S1- is bonded to three equivalent Co2+ and one S1- atom to form distorted SCo3S tetrahedra that share corners with three equivalent CoS6 octahedra and corners with three equivalent SCo3S tetrahedra. The corner-sharing octahedral tilt angles are 77°. The S–S bond length is 2.11 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiFeF3 by Materials Project

LiFeF3 is pyrite-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded to five F1- atoms to form distorted LiF5 tetrahedra that share corners with six FeF6 octahedra, corners with four equivalent LiF5 tetrahedra, and edges with two FeF6 octahedra. The corner-sharing octahedra tilt angles range from 53–71°. There are a spread of Li–F bond distances ranging from 1.93–2.53 Å. There are two inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with two equivalent FeF6 octahedra, corners with six equivalent LiF5 tetrahedra, edges with two equivalent FeF6 octahedra, and edges with two equivalent LiF5 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Fe–F bond distances ranging from 2.08–2.17 Å. In the second Fe2+ site, Fe2+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with two equivalent FeF6 octahedra, corners with six equivalent LiF5 tetrahedra, edges with two equivalent FeF6 octahedra, and edges with two equivalent LiF5 tetrahedra. The corner-sharing octahedral tilt angles are 64°. There are a spread of Fe–F bond distances ranging from 2.05–2.17 Å. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+ and two Fe2+ atoms. In the second F1- site, F1- is bonded to two equivalent Li1+ and two Fe2+ atoms to form corner-sharing FLi2Fe2 tetrahedra. In the third F1- site, F1- is bonded in a 4-coordinate geometry to two equivalent Li1+ and two Fe2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiTe2 by Materials Project

NiTe2 is pyrite-like structured and crystallizes in the cubic Pa-3 space group. The structure is three-dimensional. Ni4+ is bonded to six equivalent Te2- atoms to form corner-sharing NiTe6 octahedra. The corner-sharing octahedral tilt angles are 61°. All Ni–Te bond lengths are 2.63 Å. Te2- is bonded in a distorted trigonal planar geometry to three equivalent Ni4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Economic Extraction, Recovery and Upgrading of Rare Earth Elements from Coal-Based Resources (Final Report)

The overall objective of this project is to produce a rare earth elements product with greater than 8% rare earth elements from coal-based resources using an economically viable and environmentally benign processing methodology. The objective of the coal processing work will be to acquire appropriate coal feed and produce a viable clean coal product, a concentrated REE feed stream, and a pyrite stream (where available) that can be used to enhance leaching. The objective of the bio-oxidation portion of the project is to utilize bacteria to oxidize sulfide minerals and ferrous ions to ferric ions to accelerate leaching and remove the sulfides to prevent future acid mine drainage and related liabilities. The objective of the solution conditioning work is to remove iron and control leaching solution conditions to facilitate extraction of REEs without significant thorium extraction. The objective of the column leaching work is to engineer/model and simulate heap leaching to demonstrate low-cost extraction of REEs from coal-based resources. The objective of the solvent extraction work is to selectively extract and recover through controlled stripping of REEs that are solubilized through leaching. The objective of the precipitation portion of the project is to recover the REEs from the solvent extraction stripping solutions and dry them to achieve the final product of rare earth elements that is > 8 % REEs. The objective of the technical, economic, and environmental analysis is to determine the overall viability of the processing approach that is demonstrated in this project

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2022

Interactions between molecular-scale processes and hyporheic exchange for understanding Fe-S-C cycling in riparian wetlands (Final Report)

Wetlands represent some of the most productive ecosystems on the planet and critically influence global environmental health. Specifically, wetlands promote water quality by transforming nutrients and organic compounds and sequestering metals and contaminants. Riparian wetland hyporheic zones, where toxic surface water and anoxic groundwater mix, exhibit dynamic conditions that drive steep redox gradients and promote hotspots of diverse and fluctuating microbial activity. Changes in climate, water quality, and water quantity can disturb hydrologic flow and biogeochemical processing in these environments. Understanding how sulfate loading, impacted by hydrologic flux and anthropogenic inputs, influences iron and carbon cycling in wetlands will be crucial for predicting water quality issues driven by iron mineral precipitation and sorption, such as the release of heavy metals and other toxic elements. We used a fully integrated multi-scale and multi-method approach to develop a mechanistic understanding of how hydrologic flow influences coupled iron and sulfur cycles in riparian wetlands. This entailed hydrological, geochemical, and microbial observations at two locations: an anthropogenic sulfate-impacted riparian wetland in northern Minnesota, and a low-sulfate Fe-rich riparian wetland in Tims Branch at the Savannah River Site (SRS). These sites were characterized by hydrologically dynamic conditions where the stream and wetland systems oscillated between gaining (upward flow) and losing (downward flow) conditions that recharged the system occasionally with oxidants that fueled a variety of biogeochemical reactions. Aqueous geochemical measurements of surface water, groundwater, and porewater samples were made alongside solid-phase geochemical analyses of sediment gravity cores. Bulk X-ray absorption spectroscopy at the Advanced Photon Source (APS; Argonne) interrogated the speciation and distribution of Fe and S mineral phases of the sediments. Interestingly, it was discovered that, despite strongly reducing conditions, Fe(III) compounds and a variety of intermediate valence S compounds were stable in the subsurface. Indeed, compounds like thiosulfate, S(0), and intermediate valence organosulfur compounds were more prevalent than FeS and pyrite. The composition of the sediments did change with changes in hydrologic flow, showing their reactivity in changing redox conditions. The abundance of these intermediate S compounds was likely formed as a result of anaerobic oxidation by aqueous and solid-phase Fe(III) compounds, fueling a cryptic S cycle that is driving the breakdown of organic matter in the hyporheic zone. Microbiome surveys showed a core community that seemed stable across the landscape, but changed with increasing depth into the sediment. The community composition did not seem to change dramatically with changes in season or hydrologic flow, except for some organisms that have the potential to contribute to S cycling. More work is needed to confirm their functional activity. These fine process-scale analyses were placed within a dynamic field context using physical flow parameters from surface water and groundwater level measurements. These data helped shed light on sulfur-driven biogeochemical processes in hydrologically dynamic riparian wetlands, addressing a gap in our understanding about the impacts of pollution and other anthropogenic changes on ecologically sensitive environments.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Demonstration of Scaled-Production of Rare Earth Oxides and Critical Materials from U. S. Coal-Based Sources (Final Report)

The project objective was to demonstrate scaled production of high purity rare earth oxides (REO), nominally exceeding 90% grade, from coal refuse sources using innovative technologies that reduce cost and improve environmental outcomes relative to traditional rare earth processing technologies. The project utilized a critical material pilot plant constructed and tested as part of a previous U.S. Department of Energy project. Target performance criteria was a 50% reduction in production cost based on previous optimum values, 150% increase in recovery and greater than 2% concentrates of rare earth oxides, cobalt and manganese. Concentrate production goals were to produce a rare earth mix oxide product at a rate of 200 grams per day having a minimum purity of 50% as well as products of cobalt and manganese having a minimum purity of 2%. A previous pilot plant investigation identified acid cost as the major contributor to an operating cost that made the recovery of rare earth and other critical metals from bituminous coal sources economically challenging. As such, acid cost reduction was a major target using bio-oxidation reactors to produce sulfuric acid from naturally occurring coal pyrite. Based on laboratory data, a bio-oxidation circuit was designed for the pilot plant to produce 7.5 l/min of acid using two 11-m3 (3000 gallon) reactors equipped with 40 hp aerators for air dispersion. The pilot-scale tests revealed that acid concentration equivalent to as high as 1.0 M sulfuric acid could be continuously produced. However, the bio-acid contained exceptionally high iron concentrations, which complicated downstream processing of the pregnant leach solution (PLS). A TEA of the bio-oxidation circuit showed that production cost was approximately $0.13 per kg acid equivalent if produced using a four-day retention time in the reactors. This value represents a 48% reduction from that of purchased bulk sulfuric acid. Calcination (or roasting) studies were conducted on coarse refuse from West Kentucky No. 13 and Fire Clay coal seam sources. The test results revealed the potential to increase recovery by nearly 100% using temperatures between 500°C to 700°C with light REE recovery value being the most improved. Acid baking of the calcined products using sulfuric acid at 250°C increased heavy rare earth recovery from around 40% to 80% while decreasing the acid requirements by over 50%. The existing pilot plant was upgraded for the pilot scale demonstration of REE and CM recovery. The primary feedstocks were West Kentucky No.13 and heap leach pregnant leach solution (PLS) while a secondary feedstock was a lignite waste material from a construction sand operation. The pilot scale operation started with PLS generation through leaching followed by iron and aluminum removal, nominally at 3.3 and 4.5 pH, respectively. Leaching lixiviants used for the test were industrial grade sulfuric acid or bio-acid generated at the pilot scale facility. For most of the tests, the solid feed rate was 200 lb/hr whereas lixiviant was added at 2 gpm to provide an optimal residence time of 45 minutes. Following the contaminant removal step, several different process schematics were tested with the goal of maximizing REE recovery and purity. In the first test, direct processing of aluminum precipitation raffinate for REE recovery using oxalic acid at pH 1.5 was investigated. Overall REE recovery was approximately 45%. Unfortunately, elevated calcium content in the PLS significantly impacted the RE-Oxide product grade. Similarly, high calcium content decreased both the product purity and grades of CM products. As such, a new flowsheet was tested with the same initial process schematic but different precipitation stages for REEs and CMs at pH 6.0 and 9.0, respectively. It was noted that the overlapping precipitation behavior of Co, Ni and Zn with REEs limited the applicability of this process schematic. While this change increased the RE-Oxide grade from 36% in the first test to 87%, the loss of critical metals to the REE cake and bypass of the REEs to the CM cake significantly impacted the recovery of both REEs and CMs. Therefore, the modified process flowsheet combined oxalic acid precipitation stage raffinate and redissolved CM cake filtrate to maximize both the recovery and purity of the products. Consequently, a RE-Oxide product with 85% purity and CM cakes with over 19% Co, 38% Ni, 14% Zn and 9% Mn content were generated with significantly higher recoveries. While the modified process flowsheet improved recoveries and grades, elemental losses observed in separate precipitation and redissolution losses inspired the adaptation of a single precipitation stage at pH 9.0 for both REEs and CMs. This change was anticipated to maximize the REE recovery while minimizing the costs associated with separated redissolution and processing stages. As expected, REE recovery in this new circuit arrangement was over 56% with a product grade of over 87% RE-Oxide content. Similarly, Co, Ni, Mn, and Zn recoveries of 54%, 40%, 67%, and 66%, respectively, were achieved. Unfortunately, the elevated calcium content present in the solution due to its precipitation at pH 9.0 caused a decrease in the CM cake quality. Therefore, the final process flowsheet involved the addition of calcium oxalate precipitation following the oxalic acid precipitation stage, which effectively eliminated calcium contamination of the CM products. Finally, the pilot scale experiments conducted using bio-acid achieved comparable REE leaching recoveries to the conventional sulfuric acid leaching. Elevated iron concentration in the solution caused the co-precipitation of REEs with the iron and aluminum cake, resulting in the REE losses. Furthermore, elevated iron content bypassing the iron and aluminum precipitation stages contaminated the metal sulfide and manganese cake, respectively. A techno-economic analysis was performed based on a commercial facility capable of treating 500 tph of coal-based material. The production cost for West Kentucky No. 13 coarse refuse material ranged from approximately $500-$700/kg of total rare earth oxide whereas the lignite source had significantly lower production cost of $100-$300/kg. The significant difference in cost was due to the easier leaching characteristics of the lignite material and the higher feed concentrations. All process scenarios resulted in a negative net present value (NPV). For the lignite feedstock, laboratory REE leach recovery values were about 30% higher than the pilot plant data. Using the lab leach results, a positive net present value was achieved and the production cost decreased from $100-$300 $/kg to less than $150/kg of total REO.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2021

Effects of Carbonate Minerals on Shale-Hydraulic Fracturing Fluid Interactions in the Marcellus Shale

Natural gas extracted from tight shale formations, such as the Marcellus Shale, represents a significant and developing front in energy exploration. By fracturing these formations using pressurized fracturing fluid, previously unobtainable hydrocarbon reserves may be tapped. While pursuing this resource, hydraulic fracturing operations leave chemically complex fluids in the shale formation for at least two weeks. This provides a substantial opportunity for the hydraulic fracturing fluid (HFF) to react with the shale formation at reservoir temperature and pressure. In this study, we investigated the effects of the carbonates on shale-HFF reactions with a focus on the Marcellus Shale. We performed autoclave experiments at high temperature and pressure reservoir conditions using a carbonate-rich and a decarbonated or carbonate-free version of the same shale sample. We observed that carbonate minerals buffer the pH of the solution, which in turn prevents clay dissolution. Carbonate and bicarbonate ions also scavenge reactive oxidizing species (ROS), which prevents oxidation of shale organic matter and volatile organic compounds (VOCs). Carbonate-free samples also show higher pyrite dissolution compared to the carbonate-rich sample due to chelation reactions. This study demonstrates how carbonate minerals (keeping all other variables constant) affect shale-HFF reactions that can potentially impact porosity, microfracture integrity, and the release of heavy metals and volatile organic contaminants in the produced water.

58 GEOSCIENCES↗
DOE OSTI2021

Evaluating and Enhancing Iron Removal via Filterable Iron Precipitates Formation during Coal-Waste Bioleaching

Iron removal via jarosite precipitate formation is a commonly used technique in various hydrometallurgical processes. Excess iron removal often becomes essential to an overall metal recovery circuit. This is particularly important to processes involving iron-bearing minerals. A technique, which involved the use of pyrite to generate acid for leaching, for iron removal is critical to enabling the process. Iron removal using CaO or similar reagents is expensive and often results in lost product. In the present study, various compounds that facilitate jarosite formation, namely Na2SO4, NH4OH, KCl, and KOH, were utilized and their effect in precipitation was observed. Visual Minteq assisted simulations were run in order to evaluate favorable conditions for iron removal. Morphology and elemental composition of precipitates were analyzed using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and the phase purity was identified using X-ray diffraction analysis.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2025

Reactivity of Shale to Supercritical CO 2 : Insights from Microstructural Characterization and Mineral Phase Evolution in Caney Shales for CCUS Applications

Understanding mineral–fluid interactions in shale under supercritical CO 2 (scCO 2 ) conditions is relevant for assessing long-term geochemical containment. This study characterizes mineralogical transformations and elemental redistribution in five Caney Shale samples serving as proxies for reservoir (R1, R2, R3) and caprock (D1, D2) facies, subjected to 30-day static exposure to pure scCO 2 at 60 °C and 17.23 MPa (2500 psi), with no brine or impurities introduced. SEM-EDS analyses were conducted before and after exposure, with mineral phases classified into silicates, carbonates, sulfides, and organic matter. Initial compositions were dominated by quartz (38–47 wt.%), illite (16–23 wt.%), carbonates (12–18 wt.%), and organic matter (8–11 wt.%). Post-exposure, carbonate loss ranged from 15 to 40% in reservoir samples and up to 20% in caprock samples. Illite and K-feldspar showed depletion of Fe 2+ , Mg 2+ , and K + at grain edges and cleavages, while pyrite underwent oxidation with Fe redistribution. Organic matter exhibited scCO 2 -induced surface alteration and apparent sorption effects, most pronounced in R2 and R3. Elemental mapping revealed Ca 2+ , Mg 2+ , Fe 2+ , and Si 4+ mobilization near reactive interfaces, though no secondary mineral precipitates formed. Reservoir samples developed localized porosity, whereas caprock samples retained more structural clay integrity. The results advance understanding of mineral reactivity and elemental fluxes in shale-based CO 2 sequestration.

geochemical CO2 sequestration↗
DOE OSTI2021

Recovery and Enhanced Upgrading of Rare Earth Elements from Coal-Based Resources: Bioleaching and Precipitation

Rare earth elements (REEs) are of great importance to modern society and their reliable supply is a major concern of many industries that utilize them in metal alloys, semiconductors, electrical equipment, and defense equipment. REEs in the coal waste have been revealed to be an alternative resource for REEs production. In this study, the extraction, recovery, and upgrading of the REEs from coal waste has been realized with the bioleaching and precipitation processes. Reliable and sustainable acid and oxidant production from the oxidation of the pyrite with Acidithiobacillus ferrooxidans to generate acid for leaching were realized in this research. The acidified bioleaching solution was used to extract REEs from coal waste, with 13–14% yields for most REE elements (~72 h of leaching). However, recovery for longer duration tests was significant higher (varies from 40–60% for individual REEs). After extraction, precipitation and separation processes were designed with the aid of Visual Minteq calculations and modeling to concentrate the REEs. With the procedures designed in this research, a final REEs precipitate product containing 36.7% REEs was produced.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2020

Biogeochemical Controls on the Potential for Long-Term Contaminant Leaching from Soils Developing on Historic Coal Mine Spoil

Coal mine spoil is widespread in US coal mining regions, and the potential long-term leaching of toxic metal(loid)s is a significant and underappreciated issue. This study aimed to determine the flux of contaminants from historic mine coal spoil at a field site located in Appalachian Ohio (USA) and link pore water composition and solid-phase composition to the weathering reaction stages within the soils. The overall mineralogical and microbial community composition indicates that despite very different soil formation pathways, soils developing on historic coal mine spoil and an undisturbed soil are currently dominated by similar mineral weathering reactions. Both soils contained pyrite coated with clays and secondary oxide minerals. However, mine spoil soil contained abundant residual coal, with abundant Fe- and Mn- (oxy)hydroxides. These secondary phases likely control and mitigate trace metal (Cu, Ni, and Zn) transport from the soils. While Mn was highly mobile in Mn-enriched soils, Fe and Al mobility may be more controlled by dissolved organic carbon dynamics than mineral abundance. There is also likely an underappreciated risk of Mn transport from coal mine spoil, and that mine spoil soils could become a major source of metals if local biogeochemical conditions change.

58 GEOSCIENCES↗