Search NASA⌕ Search

SEARCH · Search NASA

Results for “Dissolution Rate”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Thermodynamic equilibrium and kinetic fundamentals of oxide dissolution in aqueous solution

Dissolution of oxides in aqueous solutions is fundamentally important for a range of applications and a critical process that determines the chemical durability of industrial ceramics, the performance of nuclear waste forms, and the chemical weathering of minerals. The thermodynamic equilibrium and kinetics of dissolution reactions are key to determining the rate at which oxides dissolve. The increase in collaborative research across disciplines in materials research necessitates a common background to tackle shared scientific problems across different fields. This review selectively examines the fundamentals of dissolution theories that have been developed in chemistry, geochemistry, and materials science, and assembles them into a single collective document for the broader materials science community. Applications of the theories are highlighted using examples from specific areas, but can be similarly applied to other areas. Challenges and future research needs for a predictive-level understanding are discussed in light of the current literature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Pb 2+ –Calcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite

The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion-mineral interactions during dissolution under far-from equilibrium conditions remains limited. Here we show that calcite (CaCO 3 ) exhibits a rich array of dissolution features in the presence of Pb. During the initial stage, calcite exhibits non-classical surface features characterized as micro pyramids developed spontaneously in acidic Pb-bearing solutions. Subsequent pseudomorphic growth of cerussite (PbCO 3 ) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded a cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution-precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing micro structures observed in naturally-occurring and synthetic carbonate minerals by dissolution. In addition, heterogeneous micro-environments created in transport limited reactions under pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.

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

Geochemical Assessment for Carbon Sequestration in the Conasauga Group, Northwest Georgia, USA

Sedimentary geological formations are known to be great candidates for geological carbon sequestration. Published studies suggest the southeast of the United States contains many formations suitable for carbon storage. The Cassville 1 Stratigraphic Borehole well could act as a potential carbon reservoir for nearby energy resource facilities in Georgia, United States. Although studies have shown that porous formations are adequate for geological carbon sequestration, it is important to understand possible geochemical reactions between CO 2 and the targeted geological formation before injecting any fluids. In this study, a sandstone sample from the Cassville 1 well is being considered for geological carbon sequestration in the Conasauga Group in Northwest Georgia. Here, the collected sandstone sample, consisting of quartz, K-feldspar, micas, kaolinite, and carbonate minerals such as calcite and dolomite, has a 6% porosity. Leveraging the formation composition and porosity, a one-dimensional continuum reactive transport model was built using CrunchFlow to assess possible geochemical reactions between injected CO 2 and the geological formation. Simulation results show that the carbonate minerals, calcite and dolomite, dissolve during the injection period of 10,000 days, increasing formation porosity from 6% to as much as 30%. The rate and extent of carbonate mineral dissolution and resulting porosity increase are highly sensitive to mineral reactive surface area values. No evidence of mineral precipitation was observed, suggesting that dissolution reactions will control porosity evolution during the CO 2 injection period.

42 ENGINEERING↗
DOE OSTI2026

Electro-carburization of mild steel through two-step reaction in molten-salt electrolyte

The rapid carburization of mild steel is demonstrated via the electrochemical deposition of solid carbon, followed by thermochemical iron-carbon (Fe-C) reaction using a molten lithium-potassium carbonate (LiKCO 3 ) salt electrolyte and carbon dioxide as the carbon source. Depth-dependent microstructural and compositional changes in the steel are shown to be controlled by the applied cell voltage and reaction temperatures. Reaction temperatures above the Fe-C eutectoid temperature promote faster carburization due to carbon dissolution into austenite. The carbon deposition rate is regulated by the applied cell voltage: At - 2.4 V, carbon deposition occurs much faster than its diffusion into the steel, resulting in the accumulation of a carbon-rich layer exceeding 1 mm, which does not diffuse into the steel. In contrast, at - 1.8 V, all deposited carbon effectively diffuses into the steel, leaving a minimal external deposit. In both cases, carbon ingress forms a carbide-rich surface layer and precipitates additional carbides along the grain boundaries within the steel electrode. This method offers a potential approach to increase the carbon content of mild or low-carbon steel feedstocks, such as scrap or direct reduced iron, for industrial applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Enhanced adsorption removal of arsenic from mining wastewater using birnessite under electrochemical redox reactions

Manganese oxides have been extensively investigated for arsenic (As) adsorption from aqueous solution. However, the effect of electrochemical redox reactions on the adsorption performance and underlying mechanism remain elusive. Herein, birnessite was used for electrochemical adsorption of As from mining wastewater at a constant cell voltage, and the effect of cell voltage and the continuous use (without desorption) performance of birnessite electrode were also evaluated. We report that at 1.2 V for 24 h, the concentrations of total As (As(T)) and As(III) in wastewater decreased from 3808.7 to 73.7 μg L -1 and 682.8 to 21.4 μg L -1 , respectively. The As(T) removal ratio increased with increasing cell voltage and reached 98.1% at 1.2 V, which was higher than that at open circuit (84.1%). The Mn 2+ concentration also significantly decreased in wastewater during As adsorption. The high potential of birnessite anode and the generation of H 2 O 2 on cathode facilitated As(III) oxidation, and the electrochemical redox reactions of birnessite contributed to the enhancement of As(T) removal. The application of cell voltage reversal could improve the utilization rate of birnessite electrodes by dissolution-recrystallization during continuous use, and the As(T) removal ratio was increased from 73.5% to 85.1% after five cycles of voltage alteration. The present work indicates that birnessite is a promising absorbent for the electrochemical adsorption of As from real wastewaters.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Effects of redox cycling of iron in nontronite on reduction of technetium

In situ technetium-99 ( 99 Tc) immobilization by Fe(II) associated with clay minerals is a potential cost-effective method for Tc remediation at contaminated sites. The oxidation state of Fe is constantly cycled in sedimentary environments, however the effect of this cycle on Tc reduction and immobilization has not yet been investigated. The objective of this project was therefore to study how multiple cycles of reduction-reoxidation of Fe-rich clay mineral, nontronite, affected its reactivity toward Tc (VII) reduction. Iron-rich nontronite NAu-2 was used as a model clay mineral. NAu-2 suspension was first bioreduced by Shewanella putrefaciens CN32, which was subsequently re-oxidized by air. Three cycles of reduction-oxidation were conducted and bioreduced NAu-2 samples from all three cycles were collected and used for Tc(VII) reduction experiments. Each redox cycle resulted in a small fraction of dissolution of small size and/or poorly crystalline NAu-2. The released Fe(II) from the dissolution was likely adsorbed onto NAu-2 surface/edge sites with a high reactivity. Upon exposure to O2, this reactive Fe(II) fraction was oxidized more rapidly than structural Fe(II) and may have accounted for a two-step reoxidation kinetics of NAu-2 associated Fe(II): rapid oxidation over first few hours followed by slow oxidation. Progressive increase of this reactive fraction of Fe(II), from increased dissolution, accounted for the successively higher rate of bioreduction and reoxidation with increased redox cycles. The same Fe redistribution accounted for two-step Tc(VII) reduction kinetics as well. Rapid Tc(VII) reduction in the first few hours may be attributed to a small fraction of highly reactive Fe(II) at the NAu-2 surface/edge sites, and more steady Tc(VII) reduction over longer time may be carried out by structural Fe(II). Similar to the increased rates of Fe(III) reduction and Fe(II) oxidation, the Tc(VII) reduction rate also increased with redox cycles and could be explained by progressive increase of the reactive Fe(II) on NAu-2 surface/edges. Iron-rich clay minerals undergo important changes after redox cycles, but eventually reach a steady state with continued reactivity toward heavy metals.

36 MATERIALS SCIENCE↗
DOE OSTI2023

AN ACID BAKING APPROACH TO ENHANCE RARE EARTH ELEMENT RECOVERY FROM BITUMINOUS COAL SOURCES

Rare earth elements (REE) are a group of 17 elements typically classified as light and heavy rare earth elements, which play a crucial role in developing the latest technologies for energy, defense, and medical sectors. Even though REEs have been found in more than 200 minerals, only bastnaesite, monazite and xenotime are commercially exploited for REE extraction. However, the recent exponential increase in REE demand has spurred countries such as the United States into research for the extraction of REEs from secondary sources such as coal, acid mine drainage, and coal ash. Several coal sources (e.g., Fire Clay seam coal) across the United States have been identified to contain elevated concentrations of rare earth elements (>600 ppm), and various researchers have investigated the feasibility of both physical and hydrometallurgical extraction techniques for rare earth concentration and subsequent extraction. However, both physical and direct leaching were concluded to be inefficient for RE beneficiation and extraction due to low recoveries. Alternatively, thermal treatment provides promising means for RE recovery from bituminous coal sources. The positive impact of thermal treatment/calcination was established to be due to the decarbonization and dehydroxylation of the clays, which released entrapped rare earth elements within the dominant minerals and converted them into an acid-soluble form. Nonetheless, the improvement in recovery was limited to the light REEs (LREEs) with an insignificant increase in the heavy REEs (HREE). It was demonstrated that the light and heavy REEs in the material were associated with difficult-to-leach minerals such as monazite, xenotime, and zircon, which were not decomposed by simple calcination due to their high thermal stability. Hence, roasting in the presence of chemicals was necessary to ensure the decomposition of those REE-containing minerals. As such, this study was focused on the acid baking treatment of bituminous coals with an aim to enhance REE recovery, especially HREEs. Based on the presence of REE minerals like monazite and xenotime, three pre-leach treatment methods, i.e., 1) roasting, 2) direct acid baking, and 3) acid baking after roasting were investigated. Roasting tests at 600 ⁰C revealed that the recovery of light REEs (LREEs) was enhanced while the recovery of HREEs remained relatively unaffected. LREE and HREE recovery values of 38.3% and 21.3%, respectively, were achieved using a 50 g/L sulfuric acid solution at 5% solid concentration and a solution temperature of 75 ⁰C for 2 hours. Comparatively, direct acid baking at 250 °C provided substantial increased LREE and HREE recovery values to approximately 49.4% and 53.0%, respectively, using an equivalent acid dosage. Recoveries were maximized to 77.0% and 79.6% for LREE and HREE, respectively, by roasting followed by acid baking. Similar results were obtained from the treatment of a second bituminous coal source. Due to strong correlations between REE and Al recovery values, tests were performed on kaolinite and illite, which were prominent clay minerals within the source coals. These experiments revealed that the REE recovery improvements were likely a result of dehydroxylation of clays and subsequent release and decomposition of REE-bearing minerals such as monazite, xenotime and zircon. Subsequently, a parametric study was conducted to identify the impact of acid baking parameters on rare earth element recovery. The factors investigated using a three-level statistical experimental program were acid baking time, acid solution concentration, baking temperature, and acid solution-to-solids ratio which were found to significantly impact REE and contaminant element (Al, Fe, and Ca) recovery. An increase in baking temperature up to around 250 ⁰C improved the light and heavy REE recovery values by more than 50 absolute percentage points relative to performances achieved when direct leaching. As aforementioned, acid baking was needed to both decompose the clay minerals and liberate the REE minerals, which allowed access for the acid to solubilize the REEs. Acid concentration of the solution used for acid baking was studied as a means of minimizing the amount of acid needed to achieve a target REE recovery. However, thermo-gravimetric and differential scanning calorimetry analysis (TGA-DSC) of sulfuric acid under oxidizing atmosphere revealed that the addition of water decreased the evaporation temperature, which explains the lower REE recovery values obtained when using acid concentrations less than 100%. Using pure sulfuric acid at an acid-to-solid ratio of 0.8:1 resulted in recovery values of around 70% for both LREEs and HREEs. The decomposition reaction time was relatively quick with 65% of the TREEs recovered within the first 10 minutes. Following the identification of optimum operating conditions through the parametric study, a systematic leaching study was carried out to examine the impact of leaching parameters, such as solid-to-liquid (S/L) ratio, temperature, and time, on REE recovery using acid baking conditions of 1:1 acid to solids ratio at 250 °C for 30 minutes. The solid-to-liquid ratio was varied from 1-20% by weight at 25 °C, 50 °C, and 75 °C solution temperatures. The results indicated that reaction time and solution temperature considerably impacted the recovery of heavy and light REEs. Interestingly, LREE recovery reduced from 68% at 5% S/L to 58% at 20%S/L, whereas HREE recovery of 78% remained unaffected. The decrease in the LREE recovery was determined to be due to La and Ce precipitation, likely through isomorphic substitution with calcium in gypsum. The kinetic data indicated that 67% LREE and 77% HREE recovery could be obtained within the first 15 minutes of the reaction, suggesting fast reaction kinetics. Furthermore, raising the solution temperature from 25 °C to 75 °C increased the LREE and HREE recovery from 60% and 32% to 67% and 79%, respectively. The kinetic modeling results demonstrated that the rate-limiting step in the LREE dissolution was diffusion and chemical reaction, whereas the HREE extraction was controlled by only chemical reaction. The leaching study concluded that using 20% S/L at 75 °C for 15 minutes maximized LREE and HREE recovery. The lab-scale precipitation study showed that Fe and Al in solution could be removed at pH 4.5 followed by REE precipitation at pH 6.0 using 6 mol/L NaOH. Finally, the bench-scale data was used to develop a process flowsheet for REE recovery from low-grade bituminous coal sources using acid baking. Finally, based on the proposed flowsheet, a concentrated RE-cake obtained through selective precipitation at pH 6.5 was re-leached using HCl at pH 1.5. The resultant leachate was used to identify the impact of various operating parameters on REE recovery and purity with an aim to maximize REE precipitation efficiency while minimizing the oxalic acid dosage. The operating parameters for this investigation were oxalic acid dosage, iron (III) contamination, solution pH and temperature. The resultant model suggested that oxalic acid dosage and reaction pH are the most significant factors for the REE precipitation efficiency, followed by the interaction of oxalic dosage and Fe concentration. Test results indicated that increasing the oxalic acid concentration from 0g/L to 80g/L improved the REE precipitation efficiency from approximately 4.2% to 95.0%. Furthermore, raising the solution pH from 0.5 to 2.5 considerably enhanced the precipitation efficiency from 0.0% to 98.9%. A solution temperature elevation decreased REE recovery, which indicated an exothermic reaction between REEs and oxalate anions. Finally, a high level of Fe contamination adversely impacted REE precipitation efficiency. The speciation analysis revealed that the dominant iron species in the solution system were Fe-(C₂O₄)₃³⁻, Fe-(C₂O₄)²⁻, and Fe-(C₂O₄)⁺, which consumed the majority of the oxalate anions

rare earth elements, acid baking, high-temperature↗
DOE OSTI2018

Non-isothermal creep aging behaviors of an Al-Zn-Mg-Cu alloy

Highlights: • A novel non-isothermal creep aging (NICA) process is proposed to improve sheet metal forming efficiency. • Appropriate heating-cooling rate is conducive to obtain desired creep deformation and material properties. • The time consumption in optimized NICA process is about half of that in conventional creep aging process. • In NICA, the precipitates formed in heating will be dissolved nearby the peak temperature and re-precipitated in cooling. - Abstract: To shorten production period and reduce manufacturing cost of high strength aluminum alloy integral panel components, a novel non-isothermal creep age forming (CAF) technology was developed. Taking an Al-Zn-Mg-Cu alloy as the case material, the non-isothermal creep aging (NICA) behavior and the conventional isothermal creep aging (ICA) behavior were comparatively investigated. The corresponding creep deformations, material performance variations and precipitate microstructure evolutions were studied by creep aging tests, mechanical property and corrosion resistance tests, and transmission electron microscope (TEM) and scanning electron microscope (SEM) characterizations. Unlike the ICA which contains short heating and cooling stages and long holding stage, the NICA only has heating and cooling stages, viz., the alloy is heated slowly and the cooling stage begins immediately when reaching the peak temperature. In the NICA process, the precipitates nucleate and grow up in the first half of heating stage, resulting in the reduction of creep rate and enhancement of mechanical strength. The coarsening of precipitates occurs in the second half of heating stage, elevating the creep rate and significantly improving the corrosion resistance. Nearby the peak temperature, the primary precipitates partially dissolve, and the creep rate, mechanical strength and corrosion resistance decrease. Distinctive from the ICA process, a secondary precipitation phenomenon takes place in the cooling stage of NICA, leading to the recovery of high mechanical strength. The higher heating-cooling rate (1 °C/min) is not beneficial to accumulating creep deformation in the shorter creep aging period, while the lower one (0.25 °C/min) causes the loss of mechanical strength due to the excessive dissolution of precipitates. The moderate heating-cooling rate (0.5 °C/min) can lead to larger creep deformation, better mechanical properties and more satisfactory corrosion resistances in the NICA treated alloy, reaching 87.0% of creep strain, 105.7% of yield strength and 97.9% of electric conductivity in the ICA treated alloy. It is worth noting that the time consumption of the optimal NICA process is only 52.9% of the ICA process.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Speciation and Aqueous Dissolution of Macronutrients in Fire Ash: Variation across Ecosystems and the Effects on Nutrient Cycling

This study investigated the speciation and aqueous dissolution of macronutrients in fire ash from diverse ecosystems and speciation of ash and smoke from laboratory burning, exploring the variations and their causes. The speciation of phosphorus (P), calcium (Ca), and potassium (K) in fire ash from five globally distributed ecosystems was characterized by using X-ray absorption spectroscopy and sequential fractionation. Aqueous dissolution of the macronutrients was measured by batch experiments at acidic and alkaline pHs. The results showed that P existed mainly as Ca phosphates, Ca as double carbonates, calcite, and sulfates, and most K was associated with Ca carbonates. Mineralogy and the relative abundance of the species were primarily controlled by elemental stoichiometry and fire temperature. Differences in Ca and P speciation existed between ash and smoke from laboratory burning, possibly caused by the temperature difference and/or mass fractionation during burning. The rates, extents, and pH dependencies of macronutrient dissolution differed among macronutrients and depended on their speciation, with K being highly soluble and the P and Ca regulated by solution pH. The variability in ash macronutrient chemistry and ecosystemspecific fire ash loads resulted in varying loads and availability of individual macronutrient from fire among ecosystems. This study provides a mechanistic understanding of how fires transform the chemistry of macronutrients and affect macronutrient returns to soils across different ecosystems, which is essential for evaluating the disturbance to ecosystem nutrient cycling by fires.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

In situ Bragg coherent X-ray diffraction imaging of corrosion in a Co–Fe alloy microcrystal

Corrosion is a major concern for many industries, as corrosive environments can induce structural and morphological changes that lead to material dissolution and accelerate material failure. The progression of corrosion depends on nanoscale morphology, stress, and defects present. Experimentally monitoring this complex interplay is challenging. Here we implement in situ Bragg coherent X-ray diffraction imaging (BCDI) to probe the dissolution of a Co-Fe alloy microcrystal exposed to hydrochloric acid (HCl). By measuring five Bragg reflections from a single isolated microcrystal at ambient conditions, we compare the full three-dimensional (3D) strain state before corrosion and the strain along the [111] direction throughout the corrosion process. We find that the strained surface layer of the crystal dissolves to leave a progressively less strained surface. Interestingly, the average strain closer to the centre of the crystal increases during the corrosion process. We determine the localised corrosion rate from BCDI data, revealing the preferential dissolution of facets more exposed to the acid stream, highlighting an experimental geometry effect. These results bring new perspectives to understanding the interplay between crystal strain, morphology, and corrosion; a prerequisite for the design of more corrosion-resistant materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Graphite Steel and Chromium-Nickel Steel Corrosion: Solution Flow Through Corrosion Experiments

The corrosion of steel, when exposed to various compositions of brines is a complex, heterogeneous process involving dissolution and precipitation of multiple solids. The rate at which elements will be released from the corrosion process under these conditions will depend, in part, on effects associated with secondary alteration phases (passivating film) that may potentially form under these conditions. Understanding these processes has required the development of sophisticated methods to sample and quantitatively characterize the composition of the steel as it corrodes and releases elements. The determination of the concentrations of both brine and steel corrosion components in solutions sampled from these tests is required to fully understand the process that may eventually lead to dissolution of corrosion products.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Basin-scale analysis of Mokelumne River Formation for multi-well CO 2 injection

Large-scale carbon sequestration will likely require multiple projects injecting CO 2 into the same subsurface formation, raising concerns about safe operation and efficient use of storage capacity. This study evaluates the long-term response of the Mokelumne River Formation in California’s Sacramento Basin to multi-megaton CO 2 injection using three geologic models of the formation and the open-source simulator GEOS. The analysis focuses on three aspects of reservoir performance: (1) average pressure increase and dissolved CO 2 mass after 30 years for varying well counts and injection rates, (2) pressure interference in a multi-well configuration, and (3) dynamic storage capacity with identification of overpressure-prone regions. The results show that average formation pressure increases linearly with injected mass, while CO 2 dissolution exhibits mixed scaling: approximately linear with the number of wells but sublinear with injection rate, indicating that distributing injection across more wells enhances dissolution more effectively than increasing per-well rates. Pressure-interference effects are significant, with lower-permeability conditions delaying their onset but amplifying their magnitude at later times. Dynamic capacity, defined by the first occurrence of pressure exceeding the local overburden-based limit anywhere in the formation, varies across geologic models and assumed overburden pressure gradients. A lower fidelity geologic model predicts nearly twice the storage capacity of the two higher fidelity models, which consistently estimate approximately 1 Gt under the upper-bound overburden pressure gradient considered for the Sacramento Basin. In all model scenarios, overpressure develops away from injection wells, particularly in higher-elevation regions, highlighting the importance of basin-scale modelling for identifying risks beyond the immediate well vicinity.

Basin-scale↗
DOE OSTI2022

A combined experimental and modelling study of granite hydrothermal alteration

Geochemical reactions can induce significant changes of rock reservoir porosity and permeability via mineral dissolution and precipitation processes, affecting the long-term fluid behaviour within various geological systems. Here, the understanding and quantification of these reactions rely on field and experimental studies and on the predictions of reactive transport models. The present study was aimed at assessing the extent to which current geochemical models integrating available mineral dissolution/precipitation rate equations can reproduce the experimental data obtained from 4 to 17-day long hydrothermal alteration experiments of a muscovite-biotite granite and, thus, help provide an accurate description of the evolution of geothermal systems within granitic reservoirs. The experiments were conducted at a constant temperature of 180 °C and over an aqueous fluid pH range of 2 to 8.5, using both mixed-flow and static batch reactors. Modelled major element (K, Al, Si, Ca, and Mg) concentrations were generally in satisfactory agreement with the corresponding measured elemental fluxes – the differences between modelled and experimental values were generally within a factor of 5 – and the predicted identity and mass of formed secondary phases were consistent with the microscopic observations of the reacted solids. However, larger differences between measured and modelled element concentrations were observed when significant amounts of secondary phases formed, notably at pH 2 to 3, and for longer-term batch experiments. Much of this concentration difference stems from the underestimation of the amounts of Al-phases formed at acid to near-neutral pH. Although an idealized rock composition was considered, the observed mismatch between model calculations and experimental data can be attributed to inadequate mineral precipitation reaction rates and a poor description of reactive surface areas in existing geochemical modelling codes. More accurate quantification of precipitation kinetics, including nucleation and growth, and improved descriptions of the temporal change of mineral surface area would enhance the predictive capabilities of reactive transport models and benefit, particularly, the efforts aimed at increasing the sustainability of EGS reservoirs.

58 GEOSCIENCES↗
DOE OSTI2013

Chlorite Dissolution Kinetics at Variable pH and Temperatures up to 275 °C

The objective of this suite of experiments was to develop a useful kinetic dissolution expression for chlorite that would be applicable over a wide range of solution pH and temperature conditions representative of subsurface conditions in natural and/or engineering geothermal reservoirs. The resulting rate equation is dependent on both pH and temperature and utilizes two specific dissolution mechanisms (an “acid” and a “neutral” mechanism). Rate parameters were derived from data collected at LLNL and available published data from Lowson et al. (2007). The form of this rate equation (Equation 1) should be easy to incorporate into most existing reactive transport codes for use in prediction of rock-water interactions in EGS systems. Specifically, we find that the dissolution of chlorite, a sheet-silicate, is relatively slow at elevated temperatures (100-275 °C), compared to other framework silicate minerals for which higher temperature kinetic data are available (e.g., quartz and feldspars; see Palandri and Kharaka, 2004). This finding is in conflict with previously reported high activation energies for chlorite based on extrapolation of low-temperature experimental data to higher temperatures. Additionally, we note that the dissolution of chlorite does not increase under alkaline conditions, as has been noted for other minerals, but rather remains at the same level as that noted for neutral conditions, with only a weak dependence on temperature. Future work includes similar rate measurements and the derivation of useful rate equations for illite, smectite, and biotite from pH 3 to 10 and 100 to 275 °C. Geochemical alteration, changing stress fields, mass transport and heat transfer incorporated into computational models are needed to optimize geothermal energy production for EGS systems. The resulting mineral rate equations from this work can be directly incorporated in modeling efforts to fully assess the impacts of geochemical alteration on long-term fracture permeability for EGS systems across the Geothermal Program. Chlorite rate equations and data have been submitted to the Geothermal Data Repository.

15 GEOTHERMAL ENERGY↗
DOE OSTI2013

Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

Rates of contaminant U(VI) release from individual size fractions of a composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through batch reactors to maintain quasi-constant chemical conditions. Variability in equilibrium adsorption among the various size fractions was determined in static batch reactors and analyzed using the surface complexation modeling approach. The estimated stoichiometric coefficients of U(VI) surface complexation reactions with respect to pH and carbonate concentrations varied with size fractions. This source of variability significantly increased the uncertainty in U(VI) conditional equilibrium constants over that estimated from experimental errors alone. A minimum difference between conditional equilibrium constants was established in order to evaluate statistically significant differences between sediment adsorption properties. A set of equilibrium and kinetic expressions for cation exchange, calcite dissolution, aerobic respiration, and silica dissolution were incorporated in a reaction-rate model to describe the temporal evolution of solute concentrations observed during the flow-through batch experiments. Parameters in the reaction-rate model, calibrated using experimental data for select size fractions, predicted the changes in solute concentrations for the bulk, <2 mm, sediment sample. Kinetic U(VI) desorption was well described using a multi-rate surface complexation model with an assumed lognormal distribution for the rate constants. The estimated mean and standard deviation were the same for all < 2mm size fractions, but differed in the 2-8mm size fraction. Micropore volumes in the varied size fractions were also similar as assessed using t-plots to analyze N2 desorption data. These findings provide further support for the link between microporosity and particle-scale mass transfer rates controlling kinetic U(VI) adsorption/desorption and for the utility of N2 desorption isotherms for characterizing pore networks that influence mass transfer rates.

Stoliker, Deborah L.↗
DOE OSTI2026

Cobalt-free and high-rate stable 5V lithium nickel manganese oxide spinel cathodes enabled via surface oxygen vacancies

Spinel LiNi 0.5 Mn 1.5 O 4 offers both the high-rate, low-cost and safety advantages of LiFePO 4 and the high energy density of LiNiₓMnᵧCo₁₋ₓ₋ᵧO₂ and LiNiₓCoᵧAlzO₂ cathodes. However, the large operating voltage of these materials induces electrolyte oxidation, which degrades the interface and drives Mn dissolution. These reactions are further exacerbated at high rates due to temperature rise. In this study, we discover that ammoniacal treatment followed by annealing introduces a high density of oxygen vacancies in the “near-surface region” of LiNi 0.5 Mn 1.5 O 4 particles. These vacancies release electrons changing the oxidation state of Mn and suppressing its tendency to oxidize the electrolyte. Further, these vacancies enhance the electrode’s electronic conductivity (by ∼3-fold) and Li + diffusivity (by ∼2-fold) greatly improving charge transport, especially when operated at high rates. This results in an across-the-board improvement in self-discharge, specific capacity, energy density, rate capability, coulombic efficiency and cycling stability. When cycled at ∼200 mA g −1 , the capacity fade averaged over 3000 cycles for the surface vacancy-enriched material is ∼0.0167% per cycle compared to an order of magnitude higher fade rate for the baseline material. In conclusion, these findings reveal the potential of targeted surface oxygen vacancy doping to develop cobalt-free and high energy density cathodes that tolerate fast charging and deliver improved cycle life.

Cobalt-free cathodes↗
DOE OSTI2016

Evidence of Technetium and Iodine from a Sodalite-Bearing Ceramic Waste Form

Current plans for nuclear waste vitrification at the Hanford Tank Waste Treatment and Immobilization Plant (WTP) lack the capacity to treat all of the low activity waste (LAW) that is not encapsulated in the vitrified product. Several technologies are being considered to treat the excess LAW. One such technology is Fluidized Bed Steam Reforming (FBSR). The FBSR process results in a granular product composed of feldspathoid mineral phases that immobilize the major components in the LAW as well as other contaminants of concern (COCs), with Tc and I expected to be present in sodalite cages formed during the process. In order to meet compressive strength requirements at the Hanford Integrated Disposal Facility (IDF), the granular product may be encapsulated in a monolith. To demonstrate the ability of the technology to serve the mission of managing excess LAW, Single Pass Flow-Through (SPFT) tests have been performed on non-radioactive granular materials and granular materials encapsulated in a geopolymer binder produced at the engineering- and bench-scale as well as a granular product produced at the bench scale with actual Hanford tank waste. SPFT tests were conducted at 40 °C for durations up to 2 months with a flow-through solution buffered at pH 9. The forward reaction rate of the non-radioactive mineral product dissolution based on Si release for the granular product was measured to be (6.2 ± 2.1) × 10-4 g/m2d for the engineering-scale product and (13 ± 4.9) × 10-4 g/m2d for the bench-scale product. The resulting non-radioactive monoliths showed forward reaction rates based on Si release of (3.4 ± 1.1) × 10-4 g/m2d for the engineering-scale material and (4.2 ± 1.5) × 10-4 g/m2d for the bench-scale material demonstrating that encapsulation of the FBSR granular product in a monolith does not significantly alter the performance of the material. Finally, an FBSR granular product created at the bench scale using actual Hanford LAW gave similar release values and also demonstrated that Re and Tc show similar release behavior with a dilute-condition release rate of (1.1 ± 0.5) × 10-4 g/m2d for Tc and (1.6 ± 0.6) × 10-4 g/m2d for Re. We believe that this is the first demonstration to show that Re and I have similar release behavior and that similar behavior of Re and Tc also occurs. These results indicate that the FBSR mineral product may be a suitable supplementary immobilization technique at the Hanford site and they also suggest that both Tc and Re occupy similar sites in the sodalite cage structure.

fluidized bed steam reforming↗
DOE OSTI2020

Controlling Metal–Organic Framework/ZnO Heterostructure Kinetics through Selective Ligand Binding to ZnO Surface Steps

Metal–organic framework (MOF) heterostructures exhibit unique properties beyond those of individual components, but their design requires an understanding of energetic and kinetic controls at MOF–substrate interfaces. Although the structural relationship has been widely used in heterostructure design, it overlooks the interplay between the organic ligand and the substrate which controls the kinetics and energetics of growth of the final structure. In this study, we used zeolitic imidazolate frameworks (ZIF-8) on ZnO as a model system to evaluate this interplay via in situ monitoring and simulations. Our results demonstrate multiple roles of the 2-methyl-imidazole (2-MIM) ligand as “dissolution-promoter”, “step-pinner”, and “terrace-binder” on the ZnO (001) face and “dissolution-promoter” and “terrace-binder” on the ZnO (100) face. Through these multiple face-specific roles, 2-MIM modulates ZnO dissolution kinetics and, hence, the Zn 2+ release rate, tuning local supersaturations that dictating the characteristic ZIF-8 crystallization kinetics on different substrate faces. The critical thickness for transition from 2D to 3D growth is dictated by competition between interfacial and strain energies. The atomic-scale mechanism of the coupled substrate dissolution and MOF growth, mediated by selective linker–substrate binding, furnishes a new synthesis pathway for other complex heterostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗