Structural Transformations in the Decomposition of Mg(OH)<sub>2</sub> and MgCO<sub>3</sub>

Kim, M. G.; Dahmen, U.; Searcy, Alan W.

doi:10.1111/j.1151-2916.1987.tb04949.x

Cited by 114 publications

(83 citation statements)

References 14 publications

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“…Even then, some MgO nanocrystals were observed in the reaction layer due to MgCO 3 decomposition to MgO + CO 2 (g) during sample thinning and/or electron-beam observation. This follows from the high sensitivity of MgCO 3 to decomposition via electron and ion beam exposure, 9 as demonstrated for single crystal MgCO 3 reference materials herein, especially when the carbonate is in nanocrystalline form. These studies indicate the silica-rich passivating layers that form during carbonation can effectively trap magnesite nuclei that form during carbonation.…”

Section: Resultsmentioning

confidence: 99%

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

McKelvy¹,

Béarat²,

Chizmeshya³

et al. 2003

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Carbonation of Mg-rich minerals offers an intriguing candidate carbon sequestration process technology, which can provide large-scale CO 2 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 challenge for viable process development is reducing process cost. This is the primary focus of the CO 2 Mineral Sequestration Working Group managed by Fossil Energy at DOE, which includes members from the Albany Research Center, Los Alamos National Laboratory, the National Energy Technology Laboratory, Penn State University, Science Applications International Corporation, and the University of Utah, as well as from our research group at Arizona State University.Carbonation of the widely occurring mineral olivine (e.g., forsterite, Mg 2 SiO 4 ) is a leading process candidate, which converts CO 2 into the mineral magnesite (MgCO 3 ). As olivine carbonation is exothermic, it offers intriguing low-cost potential. Recent studies at the Albany Research Center have found aqueous-solution carbonation is a promising approach. Costeffectively enhancing carbonation reactivity is central to reducing process cost. Many of the mechanisms that impact reactivity occur at the solid/solution interface. Understanding these mechanisms is central to the ability to engineer new and modified processes to enhance carbonation reactivity and lower cost. Herein, we report the results of our UCR I project, which focused on exploring the reaction mechanisms that govern aqueous-solution olivine carbonation using model olivine feedstock materials. Carbonation was found to be a complex process associated with passivating silica layer formation, which includes the trapping of magnesite nanocrystals within the passivating silica layers, cracking and exfoliation of the layers, silica surface migration, olivine etch pit formation, transfer of the Mg and Fe in the olivine into the product carbonate, and the nucleation and growth of magnesite crystals on/in the silica/olivine reaction matrix. These phenomena occur in concert with the large solid volume changes that accompany the carbonation process, which can substantially impact carbonation reactivity. Passivating silica layer formation appears to play a major role in inhibiting carbonation reactivity. New approaches that can mitigate the effectiveness of passivating layer formation may offer intriguing potential to enhance carbonation reactivity and lower process cost.3

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Section: Resultsmentioning

confidence: 99%

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

McKelvy¹,

Béarat²,

Chizmeshya³

et al. 2003

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“…Layer permeability is critical for PL formation via incongruent dissolution, as it facilitates both the transport of Mg ions through the layer and the formation of water and its expulsion from the layer. Close examination of the simulated PL structure suggests that even without allowing for the structural disruption associated with >Si-OH formation, it may be permeable to key species 34 associated with mineral carbonation (e.g., Mg 2+ , H + , and H 2 O), consistent with incongruent dissolution. Such permeability does not exist in our quenched thermal SiO 2 glass model, but is found for the simulated PL structures.…”

Section: Simulation Of Passivating Layer Formationmentioning

confidence: 99%

“…Both processes readily cause decomposition to MgO, consistent with earlier electron irradiation observations made on bulk MgCO 3 . 34 Thus, the nanoparticles that formed during carbonation were MgCO 3 . The MgO particles observed are artifacts formed by MgCO 3 decomposition during specimen preparation or electron beam observation.…”

Section: Controlled Particle Abrasion: Enhancing Passivating Layer Exmentioning

confidence: 99%

“…The passivating layers contain a distribution of randomly oriented crystalline nanoparticles (Figure 24b), which were identified as magnesite (MgCO 3 ) or periclase (MgO) via image analysis and FFT diffraction. As magnesite is well known to be extremely electron beam sensitive, 34 readily decomposing to periclase in the process, we conducted radiation effects experiments on both nanoparticle and bulk MgCO 3 . These studies confirmed that magnesite, especially the magnesite nanocrystals present in the passivating layers, is very sensitive to both electron irradiation effects during HREM observation/analysis and ion beam damage during specimen preparation.…”

Section: Controlled Particle Abrasion: Enhancing Passivating Layer Exmentioning

confidence: 99%

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A Novel Approach to Mineral Carbonation: Enhancing Carbonation While Avoiding Mineral Pretreatment Process Cost

Chizmeshya¹,

McKelvy²,

Squires³

et al. 2007

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Known fossil fuel reserves, especially coal, can support global energy demands for centuries to come, if the environmental problems associated with CO 2 emissions can be overcome. Unlike other CO 2 sequestration candidate technologies that propose long-term storage, mineral sequestration provides permanent disposal by forming geologically stable mineral carbonates. Carbonation of the widely occurring mineral olivine (e.g., forsterite, Mg 2 SiO 4 ) is a large-scale sequestration process candidate for regional implementation, which converts CO 2 into the environmentally benign mineral magnesite (MgCO 3 ). The primary goal is cost-competitive process development. As the process is exothermic, it inherently offers low-cost potential. Enhancing carbonation reactivity is key to economic viability. Recent studies at the U.S. DOE Albany Research Center have established that aqueous-solution carbonation using supercritical CO 2 is a promising process; even without olivine activation, 30-50% carbonation has been achieved in an hour. Mechanical activation (e.g., attrition) has accelerated the carbonation process to an industrial timescale (i.e., near completion in less than an hour), at reduced pressure and temperature. However, the activation cost is too high to be economical and lower cost pretreatment options are needed.We have discovered that robust silica-rich passivating layers form on the olivine surface during carbonation. As carbonation proceeds, these passivating layers thicken, fracture and eventually exfoliate, exposing fresh olivine surfaces during rapidly-stirred/circulating carbonation. We are exploring the mechanisms that govern carbonation reactivity and the impact that (i) modeling/controlling the slurry fluid-flow conditions, (ii) varying the aqueous ion species/size and concentration (e.g., Li , and (iii) incorporating select sonication offer to enhance exfoliation and carbonation. Thus far, we have succeeded in nearly doubling the extent of carbonation observed compared with the optimum procedure previously developed by the Albany Research Center. Aqueous carbonation reactivity was found to be a strong function of the ionic species present and their aqueous activities, as well as the slurry fluid flow conditions incorporated. High concentration sodium, potassium, and sodium/potassium bicarbonate aqueous solutions have been found to be the most effective solutions for enhancing aqueous olivine carbonation to date. Slurry-flow modeling using Fluent indicates that the slurryflow dynamics are a strong function of particle size and mass, suggesting that controlling these parameters may offer substantial potential to enhance carbonation.During the first project year we developed a new sonication exfoliation apparatus with a novel sealing system to carry out the sonication studies. We also initiated investigations to explore the potential that sonication may offer to enhance carbonation reactivity. During the second project year, we extended our investigations of the effects of sonication on the exten...

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“…This explains that why the observed decomposition produces (MgO) of magnesite are cube nano-particles. Kim et al [26] observed the structures of larger MgO clusters by using transmission electron microscopy and found that the cube-like nanoparticles with the edge length 2-3 nm.…”

Section: Growth Strategies Of (Mgo) N Clustersmentioning

confidence: 99%

Structure Stability and Growth Strategies of the (MgO)n (n=1-13) Clusters

Zhao¹,

Wang²,

Qi³

et al. 2016

Proceedings of the 2nd Annual International Conference on Advanced Material Engineering (AME 2016)

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Abstract. The thermal decomposition process of magnesite significantly affects the catalytic activity of MgO. The structure, stability and growth strategies of the (MgO) n (n = 1-13) clusters were investigated by density functional theory. From reaction energy it can be seen that the contributions of the small clusters to grow are larger at lower temperature. By analyzing the differences in Gibbs free energy between MgO crystal and (MgO) n clusters, it can be seen that at the initial decomposition temperature of magnesite (about 700K), the (MgO) n clusters with linear or distorted cubic structures become more stable than the hexagon ring structures, even the hybrid structures are more stable than the cage structures.

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Structural Transformations in the Decomposition of Mg(OH)₂ and MgCO₃

Cited by 114 publications

References 14 publications

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

A Novel Approach to Mineral Carbonation: Enhancing Carbonation While Avoiding Mineral Pretreatment Process Cost

Structure Stability and Growth Strategies of the (MgO)n (n=1-13) Clusters

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Structural Transformations in the Decomposition of Mg(OH)2 and MgCO3

Cited by 114 publications

References 14 publications

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

Understanding Olivine Co2 Mineral Sequestration Mechanisms at the Atomic Level: Optimizing Reaction Process Design

A Novel Approach to Mineral Carbonation: Enhancing Carbonation While Avoiding Mineral Pretreatment Process Cost

Structure Stability and Growth Strategies of the (MgO)n (n=1-13) Clusters

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Structural Transformations in the Decomposition of Mg(OH)₂ and MgCO₃