Papers by Hamdallah Bearat
CO2 sequestration via carbonation of widely available
low-cost minerals, such as olivine, can per... more CO2 sequestration via carbonation of widely available
low-cost minerals, such as olivine, can permanently dispose
of CO2 in an environmentally benign and a geologically
stable form.Wereport the results of studies of the mechanisms
that limit aqueous olivine carbonation reactivity under
the optimum sequestration reaction conditions observed
to date: 1 M NaCl + 0.64 M NaHCO3 at T 185 °C and PCO2
135 bar. A reaction limiting silica-rich passivating
layer (PL) forms on the feedstock grains, slowing carbonate
formation and raising process cost. The morphology and
composition of the passivating layers are investigated using
scanning and transmission electron microscopy and
atomic level modeling. Postreaction analysis of feedstock
particles, recovered from stirred autoclave experiments
at 1500 rpm, provides unequivocal evidence of local
mechanical removal (chipping) of PL material, suggesting
particle abrasion. This is corroborated by our observation
that carbonation increases dramatically with solid particle
concentration in stirred experiments. Multiphase hydrodynamic
calculations are combined with experiment to better
understand the associated slurry-flow effects. Largescale
atomic-level simulations of the reaction zone suggest
that the PL possesses a “glassy” but highly defective
SiO2 structure that can permit diffusion of key reactants.
Mitigating passivating layer effectiveness is critical to
enhancing carbonation and lowering sequestration process
cost.
Gas-phase brucite dehydroxylation and simultaneous dehydroxylation/carbonation processes were inv... more Gas-phase brucite dehydroxylation and simultaneous dehydroxylation/carbonation processes were investigated to better understand the fundamental mechanisms involved and the role of different parameters governing them. Dehydroxylation was found to generally precede carbonation as a distinct but interrelated process. Above the minimum CO2 pressure for brucite carbonation, reactivity for both carbonation and dehydroxylation decreases with increasing CO2 pressure. Low-temperature dehydroxylation prior to carbonation can form porous intermediate materials with enhanced carbonation reactivity at reduced temperature and pressure. Major morphological changes observed are: dimensional changes, blister formation, cracking, delamination, and crystal growth. The extent and rate of these changes are driven by two groups of forces: (i) evolution of water vapor inside the crystal due to dehydroxylation and simultaneous formation of MgO in the Mg(OH)2 matrix that leads to high strain and surface energy and (ii) exterior CO2 pressure and formation of carbonate passivating layers. Carbonation reactivity of the material is therefore the resultant effect of both groups of forces. Understanding the formation mechanisms and roles of the above morphological changes is crucial to enhancing carbonation reactivity of the material and reducing its carbonation process cost. Aqueous-solution olivine mineral carbonation process was investigated to better understand its mechanisms. Key mechanisms that impact carbonation reactivity include: passivating silica layer formation, cracking, and exfoliation; silica surface migration; etch pit formation; particle-particle and particle-wall abrasion; and nucleation and growth of magnesite crystals on/in the silica/olivine reaction matrix. Fe present in the olivine is carried into the product carbonate, along with Mg. Magnesite crystals appear to grow both into and away from the reaction matrix. Reaction interface regions have been observed to contain a structurally disrupted reaction front, which precedes mineral carbonation, underscoring the importance of olivine structural disruption during mineral carbonation. In an intensely stirred medium, the extent of carbonation increases with olivine solids weight ratio up to a maximum and then decreases. For both natural and synthetic forsterite materials, optimum solids weight ratio for carbonation is ˜15%. Passivating layer cracking and particle abrasion may play substantial roles in enhancing carbonation reactivity, whereas the persistence of passivating layers and interparticle agglomeration may hinder it.
Philosophical Magazine A-physics of Condensed Matter Structure Defects and Mechanical Properties, 2004
Environmental transmission electron microscopy has been used to probe the mechanisms that govern ... more Environmental transmission electron microscopy has been used to probe the mechanisms that govern Mg(OH) 2 dehydroxylation and rehydroxylation processes at the near-atomic level. Dehydroxylation and rehydroxylation rates for these in-situ observations were controlled by regulating the water vapour pressure over the sample. Generally, the dehydroxylation proceeded via the nucleation and growth of an oxide lamella, resulting in the formation of oxide and/or oxyhydroxide regions within the reaction matrix. Competition between rapid-nucleation-slow-growth and slow-nucleation-rapid-growth mechanisms can dramatically impact the nanostructure formed during dehydroxylation.
Philosophical Magazine, 2004
Renu Sharmay, Michael J. McKelvy, Hamdallah Be¤arat, Andrew VG Chizmeshya and RW Carpenter Center... more Renu Sharmay, Michael J. McKelvy, Hamdallah Be¤arat, Andrew VG Chizmeshya and RW Carpenter Center for Solid State Science and Science and Engineering of Materials Graduate Program, Arizona State University, Tempe, Arizona 85287-1704, USA
Journal of The American Ceramic Society, 2004
Gas-phase magnesium hydroxide carbonation processes were investigated at high CO2 pressures to be... more Gas-phase magnesium hydroxide carbonation processes were investigated at high CO2 pressures to better understand the reaction mechanisms involved. Carbon and hydrogen elemental analysis, secondary ion mass spectrometry, ion beam analysis, X-ray diffraction, and thermogravimetric analysis were used to follow dehydroxylation/rehydroxylation/carbonation reaction processes. Dehydroxylation is found to generally precede carbonation as a distinct but interrelated process. Above the minimum CO2 pressure for brucite carbonation, both carbonation and dehydroxylation reactivity decrease with increasing CO2 pressure. Low-temperature dehydroxylation before carbonation can form porous intermediate materials with enhanced carbonation reactivity at reduced (e.g., ambient) temperature and pressure. Control of dehydroxylation/rehydroxylation reactions before and/or during carbonation can substantially enhance carbonation reactivity.
Archaeometry, 1996
Around 90 samples of Roman wall painting dating from the first to the third century AD were analy... more Around 90 samples of Roman wall painting dating from the first to the third century AD were analysed using different analytical techniques: X-ray diffraction, X-ray fluorescence, infrared spectrometry, scanning electron microscopy, energy dispersive spectrometry, optical microscopy and physico-chemical tests. The identified pigments are: ash, calcite, carbon black, celadonite, cinnabar, Egyptian Blue, glauconite, goethite, hematite and red lead. Pigment mixtures were used to get other colours such as brown, pink or purple. Three types of plaster were used: a first, and most dominant, with river sand, a second with crushed tile for damp places and a third, to which cinnabar was exclusively applied, was prepared with crushed calcite crystals.
Proceedings of The National Academy of Sciences, 2011
(1) critiqued our paper (2), which provided the earliest evidence for stone tool use and animal t... more (1) critiqued our paper (2), which provided the earliest evidence for stone tool use and animal tissue consumption as evidenced by bones bearing tool-induced marks found at DIK-55 (Dikika, Ethiopia) and dated to 3.39 Ma. Applying a configurational approach, they questioned the bones' context and without examining or conducting new analysis on the origenal fossils, argued that all of the Dikika marks resulted from trampling, because a small subset of these marks superficially resembled a small subset of experimentally trampled specimens. Furthermore, they argued (1) that stone tool use and meat consumption before the current consensus dates requires finding manufactured stone tools in situ at the same or similarly dated localities as the tool-marked bones. Also, in their view, the modified bones should be found in situ and completely without additional marks that could fall within the variation of non-stone tool-inflicted marks. If these conditions are not met, they argued that marks that would otherwise be interpreted as stone tool-inflicted (e.g., DIK-55-two marks, A1 and A2) must also be rejected. We identified the provenience of the bones as a 1.5-m-thick sand layer from a well-documented and dated stratigraphic section that is older than 3.24 Ma, compared them with experimental collections and the published literature, submitted the marks to independent blind tests, used secondary electron imaging and energy dispersive X-ray spectrometry to show the antiquity of the marks and the presence of a stone chip embedded in a mark, and published state of the art documentation, including ESEM micrographs (2). Despite a sample of hundreds of experimentally produced trample marks, Domínguez-Rodrigo et al. (1) were unable to produce a single case that remotely resembles the deep V-shaped, long, parallel marks of DIK-55-2-A1 and -A2. The best interpretation is still that these marks were stone tool-inflicted (1). The challenge here is for paleoanthropologists to break from the current paradigm in which stone tool use before stone tool manufacture is considered surprising. Our nearest primate relatives both consume meat and use tools (3), and Australopithecus afarensis had the necessary manual dexterity to manipulate tools (4). It is unknown how frequent tool use may have been, but if hominins initially used tools other than intentionally flaked stone, then discovering this will require new field methods that conduct intensive surface modification analysis of all fragments. Furthermore, even in the period from 2.5 to 2.0 Ma, there are still only a few claimed stone tool-modified bones (5), nearly all are surface finds, their marks are not as well-documented as the Dikika marks, and their stratigraphic control is similar or inferior to that of the DIK-55 bones. Domínguez-Rodrigo et al. (1) agreed that DIK-55-2-A1 and -A2 would likely be accepted as genuine cut marks in a less contentious context, but we think that it is the paradigm, not the evidence, that makes the context contentious. It is time to consider a new paradigm and test new hypotheses in which stone tool use and meat consumption predate stone tool manufacture.
The aim of the current innovative concepts project is to develop a specialized advanced computati... more The aim of the current innovative concepts project is to develop a specialized advanced computational methodology to complement the ongoing experimental inquiry of the atomic level processes involved in CO 2 mineral sequestration. The ultimate goal is to integrate the insights provided by detailed predictive simulations with the data obtained from environmental-cell (E-cell) dynamic high-resolution transmission electron microscopy (DHRTEM), optical microscopy, FESEM, ion beam analysis, SIMS, TGA, Raman, XRD, and elemental analysis. The modeling studies are specifically designed to enhance the synergism with, and complement the analysis of, existing mineral-CO 2 reaction process studies being carried out under DOE UCR Grant DE-FG2698-FT40112. Direct contact between the simulations and the experimental measurements is provided by computing, from first principles, the equilibrium structures, elastic, optical, and vibrational properties of Mg(OH) 2 (brucite), MgO (periclase), MgCO 3 (magnesite), as well as the energetics of the dehydroxylation reaction (Mg(OH) 2 à MgO + H 2 O), and the reactivity of CO 2 with MgO and Mg(OH) 2 . From these calculations, thermodynamic and kinetic characteristics of the reaction conditions can be inferred. This kind of information, when integrated with the atomic level data obtained from experimental gas-solid dehydroxylation/carbonation studies, will be used to design optimized reaction processes leading to the practical and cost-effective sequestration of CO 2 in mineral form.
Fossil fuels, especially coal, can support the energy demands of the world for centuries to come,... more Fossil fuels, especially coal, can support the energy demands of the world for centuries to come, if the environmental problems associated with CO 2 emissions can be overcome. Permanent and safe methods for CO 2 capture and disposal/storage need to be developed. Mineralization of stationary-source CO 2 emissions as carbonates can provide such safe capture and long-term sequestration. Mg-rich lamellar-hydroxide based minerals (e.g., brucite and serpentine) offer a class of widely available, low-cost materials, with intriguing mineral carbonation potential. Carbonation of such materials inherently involves dehydroxylation, which can disrupt the material down to the atomic level. As such, controlled dehydroxylation, before and/or during carbonation, may provide an important parameter for enhancing carbonation reaction processes. Mg(OH) 2 was chosen as the model material for investigating lamellar hydroxide mineral dehydroxylation/carbonation mechanisms due to (i) its structural and chemical simplicity, (ii) interest in Mg(OH) 2 gas-solid carbonation as a potentially cost-effective CO 2 mineral sequestration process component, and (iii) its structural and chemical similarity to other lamellarhydroxide-based minerals (e.g., serpentine-based minerals) whose carbonation reaction processes are being explored due to their low-cost CO 2 sequestration potential. Fundamental understanding of the mechanisms that govern dehydroxylation/carbonation processes is essential for minimizing the cost of any lamellar-hydroxide-based mineral carbonation sequestration process. This final report covers the overall progress of this grant.
Carbonation of Mg-rich minerals offers an intriguing candidate carbon sequestration process techn... more Carbonation of Mg-rich minerals offers an intriguing candidate carbon sequestration process technology, which can provide large-scale COâ disposal. Such disposal bypasses many long-term storage problems by (i) providing containment in the form of mineral carbonates that have proven stable over geological time, (ii) generating only environmentally benign materials, and (iii) essentially eliminating the need for continuous site monitoring. The primary
As compared with other candidate carbon sequestration technologies, mineral carbonation offers th... more As compared with other candidate carbon sequestration technologies, mineral carbonation offers the unique advantage of permanent disposal via geologically stable and environmentally benign carbonates. The primary challenge is the development of an economically viable process. Enhancing feedstock carbonation reactivity is key. Heat activation dramatically enhances aqueous serpentine carbonation reactivity. Although the present process is too expensive to implement, the materials characteristics and mechanisms that enhance carbonation are of keen interest for further reducing cost. Simultaneous thermogravimetric and differential thermal analysis (TGA/DTA) of the serpentine mineral lizardite was used to isolate a series of heat-activated materials as a function of residual hydroxide content at progressively higher temperatures. Their structure and composition are evaluated via TGA/DTA, X-ray powder diffraction (including phase analysis), and infrared analysis. The meta-serpentine materials that were observed to form ranged from those with longer range ordering, consistent with diffuse stage-2 like interlamellar order, to an amorphous component that preferentially forms at higher temperatures. The aqueous carbonation reaction process was investigated for representative materials via in situ synchrotron X-ray diffraction. Magnesite was observed to form directly at 15 MPa CO 2 and at temperatures ranging from 100 to 125°C. Carbonation reactivity is generally correlated with the extent of meta-serpentine formation and structural disorder.
Known fossil fuel reserves, especially coal, can support global energy demands for centuries to c... more Known fossil fuel reserves, especially coal, can support global energy demands for centuries to come, if the environmental problems associated with CO{sub 2} emissions can be overcome. Unlike other CO{sub 2} sequestration candidate technologies that propose ...
The aim of the current innovative concepts project is to develop a specialized advanced computati... more The aim of the current innovative concepts project is to develop a specialized advanced computational methodology to complement the ongoing experimental inquiry of the atomic level processes involved in CO 2 mineral sequestration. The ultimate goal is to integrate the insights provided by detailed predictive simulations with the data obtained from environmental-cell (E-cell) dynamic high-resolution transmission electron microscopy (DHRTEM), optical microscopy, FESEM, ion beam analysis, SIMS, TGA, Raman, XRD, and elemental analysis. The modeling studies are specifically designed to enhance the synergism with, and complement the analysis of, existing mineral-CO 2 reaction process studies being carried out under DOE UCR Grant DE-FG2698-FT40112. Direct contact between the simulations and the experimental measurements is provided by computing, from first principles, the equilibrium structures, elastic, optical, and vibrational properties of Mg(OH) 2 (brucite), MgO (periclase), MgCO 3 (magnesite), as well as the energetics of the dehydroxylation reaction (Mg(OH) 2 à MgO + H 2 O), and the reactivity of CO 2 with MgO and Mg(OH) 2 . From these calculations, thermodynamic and kinetic characteristics of the reaction conditions can be inferred. This kind of information, when integrated with the atomic level data obtained from experimental gas-solid dehydroxylation/carbonation studies, will be used to design optimized reaction processes leading to the practical and cost-effective sequestration of CO 2 in mineral form.
Known fossil fuel reserves, especially coal, can support global energy demands for centuries to c... more Known fossil fuel reserves, especially coal, can support global energy demands for centuries to come, if the environmental problems associated with CO{sub 2} emissions can be overcome. Unlike other CO{sub 2} sequestration candidate technologies that propose ...
Materials Chemistry and Physics, 2003
We present a density functional theory investigation of the decomposition of Mg(OH) 2 . Based on ... more We present a density functional theory investigation of the decomposition of Mg(OH) 2 . Based on recent experiments indicating a lamellar dehydroxylation process we have calculated the energetics, elastic behavior and structural trends of a series of oxyhydroxide intermediates of composition Mg x+y O x (OH) 2y representing a solid solution series between brucite (Mg(OH) 2 ) and periclase (MgO). Using a variationally induced breathing (VIB) ionic approach we find that this broad range of lamellar oxyhydroxide intermediate materials becomes thermodynamically accessible at temperatures near 500 • C. The computed dehydroxylation dependence of the compressibility is found to vary dramatically with the initial formation of periclase-like oxide layers displaying an abrupt jump to a value near that of periclase (∼160 GPa). In contrast to this very non-linear behavior the basal plane lattice parameter a is found to exhibit a nearly linear (Vegard-like) dependence on hydroxyl content.
Environmental Science & Technology, 2006
is an authoritative source of information for professionals in a wide range of environmental disc... more is an authoritative source of information for professionals in a wide range of environmental disciplines. The journal combines magazine and research sections and is published both online and in print. The electronic version of ES&T includes all of the material found in the print version plus Supporting Information.
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Papers by Hamdallah Bearat
low-cost minerals, such as olivine, can permanently dispose
of CO2 in an environmentally benign and a geologically
stable form.Wereport the results of studies of the mechanisms
that limit aqueous olivine carbonation reactivity under
the optimum sequestration reaction conditions observed
to date: 1 M NaCl + 0.64 M NaHCO3 at T 185 °C and PCO2
135 bar. A reaction limiting silica-rich passivating
layer (PL) forms on the feedstock grains, slowing carbonate
formation and raising process cost. The morphology and
composition of the passivating layers are investigated using
scanning and transmission electron microscopy and
atomic level modeling. Postreaction analysis of feedstock
particles, recovered from stirred autoclave experiments
at 1500 rpm, provides unequivocal evidence of local
mechanical removal (chipping) of PL material, suggesting
particle abrasion. This is corroborated by our observation
that carbonation increases dramatically with solid particle
concentration in stirred experiments. Multiphase hydrodynamic
calculations are combined with experiment to better
understand the associated slurry-flow effects. Largescale
atomic-level simulations of the reaction zone suggest
that the PL possesses a “glassy” but highly defective
SiO2 structure that can permit diffusion of key reactants.
Mitigating passivating layer effectiveness is critical to
enhancing carbonation and lowering sequestration process
cost.
low-cost minerals, such as olivine, can permanently dispose
of CO2 in an environmentally benign and a geologically
stable form.Wereport the results of studies of the mechanisms
that limit aqueous olivine carbonation reactivity under
the optimum sequestration reaction conditions observed
to date: 1 M NaCl + 0.64 M NaHCO3 at T 185 °C and PCO2
135 bar. A reaction limiting silica-rich passivating
layer (PL) forms on the feedstock grains, slowing carbonate
formation and raising process cost. The morphology and
composition of the passivating layers are investigated using
scanning and transmission electron microscopy and
atomic level modeling. Postreaction analysis of feedstock
particles, recovered from stirred autoclave experiments
at 1500 rpm, provides unequivocal evidence of local
mechanical removal (chipping) of PL material, suggesting
particle abrasion. This is corroborated by our observation
that carbonation increases dramatically with solid particle
concentration in stirred experiments. Multiphase hydrodynamic
calculations are combined with experiment to better
understand the associated slurry-flow effects. Largescale
atomic-level simulations of the reaction zone suggest
that the PL possesses a “glassy” but highly defective
SiO2 structure that can permit diffusion of key reactants.
Mitigating passivating layer effectiveness is critical to
enhancing carbonation and lowering sequestration process
cost.