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Matthew J Genge - One of the best experts on this subject based on the ideXlab platform.
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Vesicle dynamics during the atmospheric entry heating of cosmic spherules
Meteoritics & Planetary Science, 2016Co-Authors: Matthew J GengeAbstract:Cosmic spherules are unique igneous objects that form by melting due to gas drag heating during atmospheric entry heating. Vesicles are an important component of many cosmic spherules since they suggest their precursors had finite volatile contents. Vesicle abundances in spherules decrease through the series porphyritic, glassy, barred, to Cryptocrystalline spherules. Anomalous hollow spherules, with large off-centre vesicles occur in both porphyritic and glassy spheres. Numerical simulation of the dynamic behaviour of vesicles during atmospheric flight is presented that indicates vesicles rapidly migrate due to deceleration and separate from non-porphyritic particles. Modest rotation rates of tens of radians s-1 are, however, sufficient to impede loss of vesicles and may explain the presence of small solitary vesicles in barred, Cryptocrystalline and glassy spherules. Rapid rotation at spin rates of several thousand radians s-1 are required to concentrate vesicles at the rotational axis and leads to rapid growth by coalescence and either separation or retention depending on the orientation of the rotational axis. Complex rapid rotations that concentrate vesicles in the core of particles are proposed as a mechanism for the formation of hollow spherules. High vesicle contents in porphyritic spherules suggest volatile-rich precursors, however, calculation of volatile retention indicates these have lost >99.9% of volatiles to degassing prior to melting. The formation of hollow spherules, by rapid spin, necessarily implies pre-atmospheric rotations of several thousand radians s-1. These particles are suggested to represent immature dust, recently released from parent bodies, in which rotations have not been slowed by magnetic damping
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An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary
Geology, 2016Co-Authors: Matthew J Genge, M Van Ginneken, J. Larsen, M D SuttleAbstract:We report the discovery of significant numbers (500) of large micrometeorites (>100 mm) from rooftops in urban areas. The identification of particles as micrometeorites is achieved on the basis of their compositions, mineralogies, and textures. All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. Four particles also contain Ni-rich metal-sulfide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile, and siderophile elements, as observed in micrometeorites from other sources. The reported particles are likely to have fallen on Earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date. The relative abundance ratio of barred olivine to Cryptocrystalline spherule types in the urban particles of 1.45 is shown to be higher than a Quaternary average of ~0.9, suggesting variations in the extraterrestrial dust flux over the past 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
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An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary
'Geological Society of America', 2016Co-Authors: Matthew J Genge, Larsen J, Van Ginneken M, Suttle MAbstract:Contrary to expectation we report the discovery of significant numbers (500) of large micrometeorites (MMs; >100 µm) from roof tops in urban areas. The identification of particles as MMs is achieved on the basis of their compositions, mineralogies and textures. All particles are silicate-dominated (S-type) cosmic spherules with sub-spherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite and iron-bearing olivine within glass. Four particles also contain Ni-rich, metal-sulphide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile and siderophile elements as observed in MMs from other sources. The reported particles are likely to have fallen on Earth in the past 6 years and thus represent the youngest large MMs collected to date. The relative abundance ratio of barred olivine to Cryptocrystalline spherule types amongst the urban particles of 1.45 is shown to be higher than a Quaternary average of ~0.9 suggesting variations in the extraterrestrial dust flux over the last 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geological column are thus unavoidable and can be a consequence of dust transport as well as major dust production events
Vhahangwele Masindi - One of the best experts on this subject based on the ideXlab platform.
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fractional and step wise recovery of chemical species from acid mine drainage using calcined Cryptocrystalline magnesite nano sheets an experimental and geochemical modelling approach
Journal of environmental chemical engineering, 2018Co-Authors: Vhahangwele Masindi, J G Ndiritu, Johannes P MareeAbstract:Abstract In this study, a process of fractional and step-wise recovery of metals from Acid Mine Drainage (AMD) using calcined Cryptocrystalline magnesite was explored. pH Redox Equilibrium (in C language) (PHREEQC) was used to complement the experimental studies. Half a liter (1/2 L) of coal mine drainage was used for chemical species recovery. The metal recovery process was done using an overhead stirrer in a step-wise fashion. Chemical species were recovered via a sequential and fractional precipitation of chemical components at varying pH gradients. Both experimental and modelling results revealed that chemical species were recovered at varying pH ranges. Fe was recovered at pH ≥ 3–3.5, gypsum at pH ≥ 4–10, Al at pH ≥ 6.5, Mn at pH ≥ 9.5, Cu at pH ≥ 7, Zn at pH ≥ 8, Pb at pH ≥ 8 and Ni at pH ≥ 9. Greater than 99% efficacy was achieved for all the chemical species at given pH regimes. The experimental results corroborated the geochemical modelling and XRD results. This technology successfully proved that calcined Cryptocrystalline magnesite can be used as a seeding material to facilitate a fractional and sequential recovery of chemical species from acid mine drainage. This will go a long way in minimising the disposal cost incurred from the generated sludge, thus, off-setting the running cost and making the acid mine drainage (AMD) treatment process environmentally friendly. This will also contribute significantly in environmental engineering processes.
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Removal of boron from aqueous solution using Cryptocrystalline magnesite
IWA Publishing, 2017Co-Authors: Vhahangwele Masindi, Mugera W. GitariAbstract:The present study aimed to evaluate the efficiency of using Cryptocrystalline magnesite to remove boron ions from aqueous systems. Batch experimental protocols were used to evaluate the adsorption capacity of magnesite for boron. Parameters optimized included: time, dosage, chemical species concentration and pH. Optimum conditions were observed to be 30 min of agitation, 1 g dosage of magnesite per 100 mL of aqueous solution and 20 mg/L initial boron concentration. Removal of boron from aqueous solution was observed to be independent of initial pH of the aqueous solution. The adsorption of boron onto magnesite was observed to fit better to pseudo-second-order kinetics than pseudo-first-order kinetics hence proving chemisorption. The intra-particle diffusion model revealed that the adsorption of boron from aqueous system occurs through multiple reaction phenomena. Adsorption isotherms proved that the removal of boron by magnesite fitted well to both Langmuir and Freundlich adsorption isotherms hence proving that both mono- and multi-site adsorption processes are taking place. Under optimized conditions, magnesite was able to attenuate the boron concentration to
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Published under a Creative Commons Attribution Licence Passive
2016Co-Authors: Vhahangwele Masindi, Mugera Wilson Gitari, Hlanganani Tutu, Marinda De BeerAbstract:remediation of acid mine drainage using Cryptocrystalline magnesite: A batch experimental and geochemical modelling approac
M D Suttle - One of the best experts on this subject based on the ideXlab platform.
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An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary
Geology, 2016Co-Authors: Matthew J Genge, M Van Ginneken, J. Larsen, M D SuttleAbstract:We report the discovery of significant numbers (500) of large micrometeorites (>100 mm) from rooftops in urban areas. The identification of particles as micrometeorites is achieved on the basis of their compositions, mineralogies, and textures. All particles are silicate-dominated (S type) cosmic spherules with subspherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite, and iron-bearing olivine within glass. Four particles also contain Ni-rich metal-sulfide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile, and siderophile elements, as observed in micrometeorites from other sources. The reported particles are likely to have fallen on Earth in the past 6 yr and thus represent the youngest large micrometeorites collected to date. The relative abundance ratio of barred olivine to Cryptocrystalline spherule types in the urban particles of 1.45 is shown to be higher than a Quaternary average of ~0.9, suggesting variations in the extraterrestrial dust flux over the past 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geologic column are thus unavoidable and can be a consequence of dust transport as well as major dust production events.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Suttle M - One of the best experts on this subject based on the ideXlab platform.
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An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary
'Geological Society of America', 2016Co-Authors: Matthew J Genge, Larsen J, Van Ginneken M, Suttle MAbstract:Contrary to expectation we report the discovery of significant numbers (500) of large micrometeorites (MMs; >100 µm) from roof tops in urban areas. The identification of particles as MMs is achieved on the basis of their compositions, mineralogies and textures. All particles are silicate-dominated (S-type) cosmic spherules with sub-spherical shapes that form by melting during atmospheric entry and consist of quench crystals of magnesian olivine, relict crystals of forsterite and iron-bearing olivine within glass. Four particles also contain Ni-rich, metal-sulphide beads. Bulk compositions are chondritic apart from depletions in the volatile, moderately volatile and siderophile elements as observed in MMs from other sources. The reported particles are likely to have fallen on Earth in the past 6 years and thus represent the youngest large MMs collected to date. The relative abundance ratio of barred olivine to Cryptocrystalline spherule types amongst the urban particles of 1.45 is shown to be higher than a Quaternary average of ~0.9 suggesting variations in the extraterrestrial dust flux over the last 800 k.y. Changes in the entry velocities of dust caused by quasi-periodic gravitational perturbation during transport to Earth are suggested to be responsible. Variations in cosmic spherule abundance within the geological column are thus unavoidable and can be a consequence of dust transport as well as major dust production events
Paulo J.m. Monteiro - One of the best experts on this subject based on the ideXlab platform.
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influence of mesostasis in volcanic rocks on the alkali aggregate reaction
Cement & Concrete Composites, 2012Co-Authors: Francieli Tiecher, Denise Carpena Coitinho Dal Molin, Marcia Elisa Boscato Gomes, Paulo J.m. MonteiroAbstract:Abstract Mesostasis material present in the interstices of volcanic rocks is the main cause of the alkali-aggregate reaction (AAR) in concretes made with these rock aggregates. Mesostasis often is referred to as volcanic glass, because it has amorphous features when analyzed by optical microscopy. However, this study demonstrates that mesostasis in the interstitials of volcanic rocks most often consists of micro to Cryptocrystalline mineral phases of quartz, feldspars, and clays. Mesostasis has been identified as having different characteristics, and, thus, this new characterization calls for a re-evaluation of their influence on the reactivity of the volcanic rocks. The main purpose of this study is to correlate the characteristics of mesostasis with the AAR in mortar bars containing basalts and rhyolites.