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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Temperature-dependent spectral emittance of bauxite and silica particle beds

Bauxite and silica particles are candidate materials for solar thermal energy storage at high temperatures. The temperature-dependent emittance of packed beds with bauxite and silica particles was measured using a newly upgraded emissometer at wavelengths 2 μm ≤ λ ≤ 16 μm and temperatures up to ~730 K. The room-temperature emittance was obtained from the measured directional-hemispherical reflectance. A fused silica disc was used to test the emissometer by comparing the measured spectral emittance with the calculated emittance from a fitted Lorentz oscillator model. For the polycrystalline silica particles and the fused silica disc, the measured emittance increases with temperature in the mid-infrared region. The underlying mechanism is interpreted as the temperature-dependent damping coefficient in the Lorentz oscillator model. Two types of bauxite particles with different compositions and sizes were investigated. For λ > 10 μm, the measured emittance at elevated temperatures is higher than that at room temperature. In the region 2 μm < λ < 6 μm, the temperature dependence varies for different types of particles. The total emittance of bauxite particle beds was calculated by spectral integration using Planck’s distribution at the prescribed temperature. As a result, the calculated total emittance is between 0.89 and 0.96, but it does not change monotonically with temperature.

42 ENGINEERING↗
DOE OSTI2014

Feasible conversion of solid waste bauxite tailings into highly crystalline 4A zeolite with valuable application

Highlights: • Concept to convert waste to valuable product is carried out in this study. • An industrially feasible and cost-effective approach was developed and optimized. • Highly crystalline and well-defined zeolite was produced under moderate conditions. • The zeolite derived from the bauxite tailings displayed high ion exchange capacity. • Bauxite tailings have potential application in heavy metal ions adsorbent. - Abstract: Bauxite tailings are a major type of solid wastes generated in the flotation process. The waste by-products caused significant environmental impact. To lessen this hazardous effect from poisonous mine tailings, a feasible and cost-effective solution was conceived and implemented. Our approach focused on reutilization of the bauxite tailings by converting it to 4A zeolite for reuse in diverse applications. Three steps were involved in the bauxite conversion: wet-chemistry, alkali fusion, and crystallization to remove impurities and to prepare porous 4A zeolite. It was found that the cubic 4A zeolite was single phase, in high purity, with high crystallinity and well-defined structure. Importantly, the 4A zeolite displayed maximum calcium ion exchange capacity averaged at 296 mg CaCO{sub 3}/g, comparable to commercially-available zeolite (310 mg CaCO{sub 3}/g) exchange capacity. Base on the optimal synthesis condition, the reaction yield of zeolite 4A from bauxite tailings achieved to about 38.43%, hence, this study will provide a new paradigm for remediation of bauxite tailings, further mitigating the environmental and health care concerns, particularly in the mainland of PR China.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Addressing technical barriers for reliable, safe removal of fluoride from drinking water using minimally processed bauxite ores

Throughout the developing world, over 200 million people drink groundwater containing fluoride concentrations surpassing the World Health Organization's maximum recommended contaminant level (WHO-MCL) of 1.5 mg F - /L, resulting in adverse health effects ranging from mottled tooth enamel to debilitating skeletal fluorosis. Existing technologies to remove fluoride from water, such as reverse osmosis and filtration with activated alumina, are expensive and are not accessible for low-income communities. Our group and others have demonstrated that minimally-processed bauxite ores can remove fluoride to safe levels at a fraction of the cost of activated alumina. We report results from testing for some technical challenges that may arise in field deployment of this technology at large scale, particularly in a sufficiently robust manner for application in development contexts. Anticipating possible modes of failure and addressing these challenges in advance in the laboratory is particularly important for technologies for vulnerable communities where the opportunity to re-launch pilot projects is limited and small failures can keep solutions from the people that need them most. This work addresses three potential technical barriers to reliable removal of fluoride from drinking water with bauxite ore from Visakhapatnam, Andhra Pradesh, India. We evaluate competition from co-occurring ions, adsorption reversibility, and potability of the product water with regards to leaching of undesirable ions during treatment with various adsorbent materials including raw and thermally activated bauxite, and synthetic gibbsite (a simple model system). Under the conditions tested, the presence of phosphate significantly impacts fluoride adsorption capacity on all adsorbents. Sulfate impacts fluoride adsorption on gibbsite, but not on either bauxite adsorbent. Nitrate and silicate (as silicic acid), tested only with gibbsite, do not affect fluoride adsorption capacity. Both thermally activated bauxite and gibbsite show non-reversible adsorption of fluoride at a pH of 6. Raw bauxite leached arsenic and manganese in a TCLP leaching test at levels indicating the need for ongoing monitoring of treated water, but not precluding safe deployment of bauxite as a fluoride remediation technology. Understanding these phenomena is crucial to ensure field deployment over large diverse geographical areas with aquifers varying in groundwater composition, and for ensuring that the appropriate engineering processes are designed for field implementation of this innovation.

42 ENGINEERING↗
DOE OSTI2017

Factors Governing the Performance of Bauxite for Fluoride Remediation of Groundwater

Globally, 200 million people drink groundwater contaminated with fluoride concentrations exceeding the World Health Organization's recommended level (WHO-MCL = 1.5 mg F - /L). This study investigates the use of minimally processed (dried/milled) bauxite ore as an inexpensive adsorbent for remediating fluoride-contaminated groundwater in resource-constrained areas. Adsorption experiments in synthetic groundwater using bauxites from Guinea, Ghana, U.S., and India as single-use batch dispersive media demonstrated that doses of ~10-23 g/L could effectively remediate 10 mg F - /L. To elucidate factors governing fluoride removal, bauxites were characterized using X-ray fluorescence, X-ray diffraction, gas-sorption analysis, and adsorption isotherms/envelopes. All ores contained gibbsite, had comparable surface areas (~14-17 m 2 /g), had similar intrinsic affinities and capacities for fluoride, and did not leach harmful ions into product water. Fluoride uptake on bauxite -primarily through ion-exchange- was strongly pH-dependent, with highest removal occurring at pH 5.0-6.0. Dissolution of CaCO 3 , present in trace amounts in India bauxite, significantly hindered fluoride removal by increasing solution pH. We also showed that fluoride remediation with the best-performing Guinea bauxite was ~23-33 times less expensive than with activated alumina. In conclusion, overall, our results suggest that bauxite could be an affordable fluoride-remediation adsorbent with the potential to improve access to drinking water for millions living in developing countries.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Effective Remediation of Groundwater Fluoride with Inexpensively Processed Indian Bauxite

India represents one-third of the world’s fluorosis burden and is the fifth global producer of bauxite ore, which has previously been identified as a potential resource for remediating fluoride-contaminated groundwater in impoverished communities. In this work, we use thermal activation and/or groundwater acidification to enhance fluoride adsorption by Indian bauxite obtained from Visakhapatnam, an area proximate to endemic fluorosis regions. We compare combinatorial water treatment and bauxite-processing scenarios through batch adsorption experiments, material characterization, and detailed cost analyses. Heating Indian bauxite above 300 °C increases available surface area by > 15× (to ~170 m 2 /g) through gibbsite dehydroxylation and reduces the bauxite dose for remediating 10 ppm F – to 1.5 ppm F – by ~93% (to 21 g/L). Additionally, lowering groundwater pH to 6.0 with HCl or CO 2 further reduces the average required bauxite doses by 43–73% for ores heated at 300 °C (~12 g/L) and 100 °C (~77 g/L). Product water in most examined treatment scenarios complies with EPA standards for drinking water (e.g., As, Cd, Pb, etc.) but potential leaching of Al, Mn, and Cr is of concern in some scenarios. Among the defluoridation options explored here, bauxite heated at 300 °C in acidified groundwater has the lowest direct costs ($6.86 per person per year) and material-intensity.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Characteristics of Calcium-Aluminate Slags and Pig Iron Produced from Smelting-Reduction of Low-Grade Bauxites

Low-grade bauxite ores are not favorable in the conventional Bayer process for alumina production, as they are producing more bauxite residue (red mud) and accompanying lower alumina yield than high-grade ores. In the current study, the thermodynamics and characterization of calcium-aluminate slags and pig iron produced from smelting reduction of high iron- and silica-containing bauxites are studied. Coke and limestone are used to reduce the iron oxide and adjust the basicity of slag during smelting. There is evidence that complete iron separation from bauxite is feasible through smelting-reduction process, and up to 99.9 pct of iron can be eliminated. Moreover, it is shown that the partial separation of silicon, titanium, and other elements from the Al{sub 2}O{sub 3}-containing slag occurs. The phase compositions and the distribution of elements between the metal and slag phases provide information about the high-temperature behavior of the bauxite components during smelting reduction. Employing electron microscopy analysis, it is indicated that the morphologies of CaO·Al{sub 2}O{sub 3}, 12CaO·7Al{sub 2}O{sub 3}, 2CaO·Al{sub 2}O{sub 3}·SiO{sub 2}, and CaO·Al{sub 2}O{sub 3}·SiO{sub 2} phases in the slag, as well as the complex oxides of Ca-Al-Si-Ti in the slag behave differently as the mass ratio of Al{sub 2}O{sub 3}/(Fe{sub 2}O{sub 3 }+ SiO{sub 2}) in the bauxite changes. It is also shown that the phases of slag produced from smelting-reduction below 5 K s{sup −1} of cooling rate are proper for further leaching process.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Toward Greener and More Sustainable Manufacture of Bauxite-Derived Adsorbents for Water Defluoridation

The bauxite-derived adsorbent, activated alumina (AA), has a current annual global market of over 600 million USD, and of this, more than one-third of AA is used for defluoridation of fluoride-bearing water. The commonly used Bayer process for production of AA suffers from thermodynamic inefficiency, thereby raising costs, and also causes significant environmental damage. Here, we evaluate three other bauxite-derived adsorbents as alternatives to AA for water defluoridation: Mildly processed bauxite, thermally activated bauxite, and acid-treated thermally activated bauxite (ATAB). We first determine the energy intensity and resource efficiency of these three new adsorbents throughout their (future, anticipated) manufacturing processes and compare their defluoridation performance in the laboratory. Then, we quantify the carbon footprints of the three adsorbents via the product life-cycle approach, from their manufacturing to their applications in defluoridation. The results reveal that these three adsorbents exhibit less energy intensity and higher resource efficiency, thereby lowering their carbon footprints by 2-20×, relative to an equivalent amount of AA. We also estimate the operating costs of manufacturing and potential revenues from carbon offsets for each of the three adsorbents. Replacement of about 33 000 tonnes per year of AA currently used for wastewater treatment with equivalent ATAB could annually reduce annual manufacturing costs by 4.7 million USD and additionally generate 79 200 tonnes CO 2 offsets. Finally, this study supports decision-making on selecting a greener and more sustainable approach for wastewater defluoridation.

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

Chapter 12 - Addressing Groundwater Fluoride Contamination Using Inexpensively Processed Bauxite

Globally, 200 million people are at risk of adverse health effects from drinking groundwater contaminated with high fluoride concentrations that exceed the World Health Organization's maximum contaminant limit (WHO MCL=1.5ppmF-). Although many defluoridation technologies have been demonstrated to work in lab, most have proven inappropriate for impoverished rural regions of developing countries because they are cost-prohibitive, require skilled labor, or are difficult to scale. The authors submit evidence for the use of bauxite, an aluminum-rich ore, as a potentially inexpensive, effective, and scalable defluoridation technology. Specifically, we present results from experimental studies that characterize globally diverse bauxite ores, elucidate fluoride removal mechanisms, and establish proof of concept that mildly processed bauxite can cost-effectively remediate field-relevant fluoride concentrations in synthetic and real groundwater matrices at field-relevant kinetics. We discuss practical implications of these research findings and highlight remaining challenges and unknowns that need to be further studied before implementing the proposed defluoridation process in the field.

Gadgil, AJ↗
DOE OSTI2021

Boosting the use of bauxite residue (red mud) in cement - Production of an Fe-rich calciumsulfoaluminate-ferrite clinker and characterisation of the hydration

Highlights: • Incorporation of 35 wt% of bauxite residue for production of CSAF clinker • Thermochemical calculations as suitable tool for predicting phase assemblage • Hydration of the cement was found to be accelerated in contrast to other CSA cements. • High early compressive strengths of 40 MPa In the present work, calciumsulfoaluminate-ferrite clinker was produced using 35 wt% of bauxite residue in combination with alumina, clay, limestone and gypsum. At a temperature of 1300 °C, the hydraulic phases ye'elimite, ferrite and C{sub 2}S were formed. Computed thermochemical predictions were a significantly better match for the real mineralogy than modified Bogue equations. Hydration of the clinker led to the formation of ettringite and monosulfate, resulting in compressive strengths of 17 MPa after 28d. Compressive strengths of 40 MPa after 2d, and 28d-strengths exceeding 50 MPa, were reached in blends with 10 wt% of anhydrite. The strength development was due to the rapid formation of ettringite, mainly originating from ye'elimite, which did not convert to AFm phases and led to a compact microstructure. Only when the ye'elimite dissolution decreased, did the ferrite phase react. In pastes with additional sulfates, ferrite hydration led to the formation of ettringite and to hydrogarnet. Cement nomenclature is used in this work.{sup 1}.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Extracting Critical Metals from Authentic Bauxite Residue

Securing domestic sources of critical minerals (CM) is paramount to ensuring a robust and self-sustaining technology infrastructure. Utilizing untapped non-conventional sources, like acid mine drainage, coal ash, bauxite residue/red mud, and more is an emerging approach that addresses this national concern while identifying new value-added pathways originating from waste streams. Red mud is a byproduct of the Bayer process that produces alumina and contains a wealth of CM – 50 µg/g Ga, 2.9 mg/g total rare earth elements plus yttrium, 12 mg/g Mn, 58 mg/g Al, and others. About 170 MM tonnes of red mud are co-produced annually alongside the 142 MM tonnes of alumina generated, highlighting the abundancy of this feedstock. In this work, different strategies were explored for extracting CM from authentic bauxite residue that involve thermal heating, microwave heating, and sonication all with different acids and buffers. CM recovery was then explored one step further by testing the adsorption of the extracted metals onto NETL’s Multi-functional Sorbent Technology (MUST). Microwave treatment of red mud proved the most effective CM extraction, whereas sonication was less desirable due to scale-up concerns. Successful recovery of CM from this leachate with MUST supports further studies toward optimizing the overall process.

bauxite residue↗
DOE OSTI2019

On the Conversion of Bauxite Ores to Highly Activated Alumina Media for Water Remediation

Good quality drinking water is necessary to maintain a high quality of life. Millions lack access to clean and safe drinking water, and current trends suggest that billions will face acute water shortages in the coming decades. Development of new materials has led to technological impacts on water purification, from desalination membranes to atmospheric water scavenging. However, the most challenging aspect of technological solutions is cost: if the community being serviced cannot afford the solution, it is not likely to be sustainable. Repurposing Earth-abundant materials to replace highly engineered solutions is an atractive solution. Herein, minimal processing of bauxite rocks produces a high-porosity and reactive activated alumina in situ, without purification directly from the ore. This acid-treated, thermally activated bauxite (ATAB) exhibits a high surface area of 401 ± 6 m 2 g -1 , a 40-fold increase relative to its parent ore, and a 2× increase relative to the state-of-the-art fluoride adsorbent, activated alumina. The composition, preparation, and mechanism of adsorption are studied by X-ray diffraction, X-ray photoelectron spectroscopy, and multiple-quantum magic-angle spinning 27 Al nuclear magnetic resonance (NMR). Finally, the maximum adsorption density of ATAB is comparable with that of activated alumina, but ATAB requires fewer processing steps, thus warranting future consideration as a primary adsorbent of choice for fluoride removal from water.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Evaluation of sintered bauxite proppant for binary enhanced geothermal systems

Abstract Solid granular proppant particles are widely used in oil and gas development to sustain permeability through fractures after hydraulic stimulation. Similar proppants are of interest for geothermal applications where the goal of sustaining permeability is the same, but the harsh geothermal environment risks rapid proppant degradation that will reduce fracture permeability. Here, we present proppant conductivity experiments using saw cut granite, tensile fractured granite, and aluminum control specimens packed with sintered bauxite ceramic proppants at concentrations of 0.0, 0.1, and 1.0 kg/m 2 . Simulated geothermal conditions included temperatures up to 130 °C and normal closure stresses up to 60 MPa. Compared to unpropped specimens, peak fracture conductivity enhancement was up to 6 orders of magnitude. At simulated geothermal conditions, proppants were able to sustain fracture conductivity over 60 h, but chemical dissolution and decreasing permeability over time were evident. Irreversible conductivity reductions with crushing and embedment of proppants during loading stages were also observed. Overall, sintered bauxite proppant remains a promising option for low-temperature binary-cycle enhanced geothermal systems.

58 GEOSCIENCES↗
DOE OSTI2023

A numerical study of the spectral radiative properties of packed bed with mixed bauxite and silica spheres

Bauxite and silica particles have gained increasing attention for applications in the field of concentrated solar power. In this work, a Monte Carlo ray-tracing simulation is performed to predict the radiative properties (absorptance, reflectance, and transmittance) of packed beds with mixed bauxite and silica spherical particles at wavelengths of 0.5, 2.6, 9.0, and 9.35 µm. These wavelengths are representative for the visible, near-infrared, and the mid-infrared regions that are important for solar and thermal radiation, respectively. A repeating unit-column approach is used to mathematically represent the particle bed. The effects of particle mixing ratio, volume fraction, and wavelength on the predicted radiative properties are examined. The obtained radiative properties are inputted to an inverse method to retrieve the effective absorption and scattering coefficients as well as the scattering albedo, which may be later used in a continuous-scale radiative heat transfer analysis. Furthermore, the independent scattering model is used to obtain the absorption coefficient and scattering albedo based on the absorption and scattering cross sections predicted by a Monte Carlo algorithm for a single particle. It is shown that the independent scattering model underpredicts the scattering coefficient for opaque particles but overpredicts the scattering coefficient for semitransparent particles for sufficiently high particle volume fractions. Here, the radiative properties calculated from the independent scattering model are compared to the full Monte Carlo simulation of the particle bed to examine the influence of particle mixing on dependent scattering.

42 ENGINEERING↗
DOE OSTI2021

Measurements of scattering and absorption properties of submillimeter bauxite and silica particles

Submillimeter solid particles have been considered as thermal storage media for concentrated solar power applications. Knowledge of the scattering and absorption properties of individual particles is crucial for modeling the radiative heat transfer of the particle bed. In this work, a laser scatterometer is used to measure the single-particle scattering properties at a wavelength of 635 nm by using two configurations: (1) a falling particle curtain and (2) a taped particle layer. Because a one-particle nominal thickness is formed with area fractions of 5-55% depending on the configuration, multiple scattering is minimized and hence the single scattering phase function, averaged over all illuminated particles, is directly measured. Bauxite-based ceramic particles that are strongly absorbing in the solar spectrum and silica particles that are nonabsorbing in the visible and near-infrared are investigated. The directional-hemispherical reflectance and transmittance of the taped particles are also measured to deduce the forward and backward scattering efficiency factors and the absorption efficiency factors. Only weak wavelength dependence is observed in the measured region from 380 nm to 1020 nm. Furthermore, the scattering phase functions of all bauxite-based particles with varying sizes and compositions are very similar and can be fitted to a Henyey-Greenstein phase function with an asymmetry factor g = -0.20. For the silica particles, forward scattering dominates and g = 0.45 yields the best fit. A Monte Carlo method is developed to model the particle scattering characteristics, and reasonable agreements between the modeling and experimental results are observed by introducing a specularity parameter.

42 ENGINEERING↗
DOE OSTI2014

Hidden values in bauxite residue (red mud): Recovery of metals

Highlights: • Current iron recovery techniques using red mud are depicted. • Advantages and disadvantages exist in different recovering processes. • Economic and environmental friendly integrated usage of red mud is promising. - Abstract: Bauxite residue (red mud) is a hazardous waste generated from alumina refining industries. Unless managed properly, red mud poses significant risks to the local environment due to its extreme alkalinity and its potential impacts on surface and ground water quality. The ever-increasing generation of red mud poses significant challenges to the aluminium industries from management perspectives given the low proportion that are currently being utilized beneficially. Red mud, in most cases, contains elevated concentrations of iron in addition to aluminium, titanium, sodium and valuable rare earth elements. Given the scarcity of iron supply globally, the iron content of red mud has attracted increasing research interest. This paper presents a critical overview of the current techniques employed for iron recovery from red mud. Information on the recovery of other valuable metals is also reviewed to provide an insight into the full potential usage of red mud as an economic resource rather than a waste. Traditional hydrometallurgy and pyrometallurgy are being investigated continuously. However, in this review several new techniques are introduced that consider the process of iron recovery from red mud. An integrated process which can achieve multiple additional values from red mud is much preferred over the single process methods. The information provided here should help to improve the future management and utilization of red mud.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Recovery of Scandium from Bauxite Residue Using Sulfation Roasting-Assisted Water Leaching Process

Here, this study presents a method for recovering scandium from Indonesian bauxite residue (red mud) through a sulfation roasting-assisted water leaching process. Ammonium sulfate, (NH 4 ) 2 SO 4 , was chosen as the sulfate source for its lower melting point, less corrosivity, decreased toxicity, and the potential for ammonia recovery. A modified mixing system was introduced to improve the distribution of (NH 4 ) 2 SO 4 on red mud particles by combining them in water. A series of experiments were conducted to optimize the sulfation roasting process by examining the effects of the (NH 4 ) 2 SO 4 /red mud ratio, temperature, and roasting time. Subsequently, water leaching was optimized while considering the effect of leaching time and liquid-to-solid (L/S) ratio. The leaching of scandium from the roasted red mud showed rapid kinetics, even when using only water. Under the roasting conditions of 1/1 (g/g) (NH 4 ) 2 SO 4 /red mud ratio, 700°C, 60 min roasting time, and the leaching conditions of 65°C, 60 min, and 10 mL/g (L/S), over 90% of scandium was recovered, along with 64.4% Al leaching and below 8% Fe leaching. These results were further corroborated through comprehensive analyses such as x-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). This study offers insights into an alternative, more environmentally friendly method for Sc recovery from red mud, promoting the sustainable use of hazardous waste like red mud.

ammonium sulfate↗
DOE OSTI2023

A Comparative Radiative Property Evaluation of Sintered Bauxite and AMS4003 Ceramic Particles

The radiative properties of sintered bauxite (ACCUCAST ID80) and AMS4003 particles were measured and compared to assess their performances as direct absorption and heat transfer media for particle-based concentrated solar power (CSP) plants. Reflectance measurements were performed over the spectral range 0.2–20 µm and used to calculate solar and thermal emission properties of the particles. In addition, reflectance was measured as a function of temperature up to 1000 °C for the spectral range 1–20 µm. The solar absorptance of AMS4003 was greater than that of ACCUCAST both before and after thermal cycling of the materials at 1000 °C, although thermal cycling was found to substantially decrease the solar absorptance of both materials. The thermal emittance of AMS4003 was also greater than that of ACCUCAST at all temperatures tested. Finally, the radiaitve properties measured in this study were used to estimate absorber efficiencies as a way to compare the particles in terms of their performance in a solar receiver. AMS4003 yielded greater efficiencies than ACCUCAST, suggesting its potential as a material for CSP.

14 SOLAR ENERGY↗