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Near-infrared investigation of folding sepiolite

  • Maria Tsampodimou , Vanessa-Jane Bukas , Elizabeth T. Stathopoulou , Vassilis Gionis and Georgios D. Chryssikos EMAIL logo
Published/Copyright: January 10, 2015
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American Mineralogist
From the journal American Mineralogist Volume 100 Issue 1

Abstract

Sepiolite is an industrially important clay mineral of the palygorskite-sepiolite group with alternating 2:1 ribbons and hydrated tunnels. Dry sepiolite, Mg8Si12O30(OH)4(OH2)4, loses half of its OH2 content upon further heating and undergoes a structural collapse known as folding. This treatment is considered essential for enhancing the absorptive properties of the clay. In this paper, the folding process is studied by near-infrared (NIR) spectroscopy, mid-infrared attenuated total reflectance (ATR), and thermogravimetric analysis (TGA). The folded state, Mg8Si12O30(OH)4(OH2)2, reveals a new spectrum of fundamental and higher-order OH2 vibrations, as well as systematically split doublets of structural and surface O-H vibrations. Detailed assignments for the stretching, combination, and overtone O-H modes are proposed on the basis of the two non-degenerate populations of Mg3OH (and SiOH) present in the folded state. It is demonstrated that NIR is of particular diagnostic value in monitoring conveniently and non-invasively the folding process, which appears as a simple transition between well-defined dry- and folded-structures. At the level of elementary sepiolite particles (laths), folding is described as a cooperative process requiring the integrity of the ribbons and the inter-ribbon linkages (moderately acid-leached sepiolite does not fold). This is opposed to the skewed and sometimes complex OH2 desorption trace observed by high-resolution TGA, which appears to indicate a multimodal distribution of laths. It is proposed that the rate-determining step for a sepiolite (also, palygorskite) lath to fold is the creation of a critical zone at mid-particle length, which is OH2-deficient and contains unstable, fivefold-coordinated Mg2+.

Keywords: Sepiolite; palygorskite; folding; acid activation; near-infrared spectroscopy; ATR; highresolution TGA
Received: 2014-3-26
Accepted: 2014-7-19
Published Online: 2015-1-10
Published in Print: 2015-1-1

© 2015 by Walter de Gruyter Berlin/Boston

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  3. Mineral evolution and Earth history
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  5. The rapid expansion of environmental mineralogy in unconventional ways: Beyond the accepted definition of a mineral, the latest technology, and using nature as our guide
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  7. The structure of water-saturated carbonate melts
  8. In-situ measurements of fluorine and chlorine speciation and partitioning between melts and aqueous fluids in the Na2O-Al2O3-SiO2-H2O system
  9. High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultrahigh-pressure chromitites in ophiolites
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  16. Chlorine-hydroxyl diffusion in pargasitic amphibole
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  19. Atomistic simulation on mixing thermodynamics of calcite-smithsonite solid solutions
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  25. Phase relationships in the system K2CO3-CaCO3 at 6 GPa and 900–1450 °C
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  27. Synthetic and natural ammonium-bearing tourmaline
  28. Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas
  29. Nuragheite, Th(MoO4)2·H2O, The Second Natural Thorium Molybdate And Its Relationships To Ichnusaite And Synthetic Th(MoO4)2†
  30. Structural Effects On Incorporated Water In Carbonated Apatites
  31. New Constraints On Electron-Beam Induced Halogen Migration In Apatite
  32. Origin Of The Lunar Highlands Mg-Suite: An Integrated Petrology, Geochemistry, Chronology, And Remote Sensing Perspective
  33. An In Situ High-Pressure Nmr Study Of Sodium Coordination Environment Compressibility In Albite Glass
  34. Hydrothermal Synthesis And Crystal Structure Of Also4(Oh): A Titanite-Group Member
  35. New Mineral Names
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https://doi.org/10.2138/am-2015-4988
Keywords for this article
Sepiolite; palygorskite; folding; acid activation; near-infrared spectroscopy; ATR; highresolution TGA

Articles in the same Issue

  1. The American Mineralogist at 100 years, and a mineralogy renaissance
  2. At the blurry edge of mineralogy
  3. Mineral evolution and Earth history
  4. Franciscan geologic history constrained by tectonic/olistostromal high-grade metamafic blocks in the iconic California Mesozoic-Cenozoic accretionary complex
  5. The rapid expansion of environmental mineralogy in unconventional ways: Beyond the accepted definition of a mineral, the latest technology, and using nature as our guide
  6. Microelectronic junctions in arsenian pyrite due to impurity and mixed sulfide heterogeneity
  7. The structure of water-saturated carbonate melts
  8. In-situ measurements of fluorine and chlorine speciation and partitioning between melts and aqueous fluids in the Na2O-Al2O3-SiO2-H2O system
  9. High-pressure high-temperature transitions in MgCr2O4 and crystal structures of new Mg2Cr2O5 and post-spinel MgCr2O4 phases with implications for ultrahigh-pressure chromitites in ophiolites
  10. Mid-infrared emission spectroscopy and visible/near-infrared reflectance spectroscopy of Fe-sulfate minerals
  11. Megacrystic zircon with planar fractures in miaskite-type nepheline pegmatites formed at high pressures in the lower crust (Ivrea Zone, southern Alps, Switzerland)
  12. Tourmaline as a petrogenetic monitor of the origin and evolution of the Berry-Havey pegmatite (Maine, U.S.A.)
  13. Applications of Hirshfeld surfaces to mineralogy: An example of alumohydrocalcite, and the classification of the dundasite group minerals
  14. Optical absorption anisotropy of high-density, wide-gap, high-hardness SiO2 polymorphs seifertite, stishovite, and coesite
  15. The system Na2CO3-FeCO3 at 6 GPa and its relation to the system Na2CO3-FeCO3-MgCO3
  16. Chlorine-hydroxyl diffusion in pargasitic amphibole
  17. The use of cation-cation and anion-anion bonds to augment the bond-valence model
  18. AIM analysis and the form of the bond-valence equation
  19. Atomistic simulation on mixing thermodynamics of calcite-smithsonite solid solutions
  20. Combined geochemistry and geochronology constrains coupled subduction of oceanic and continental crust in the Huwan shear zone, central China
  21. Near-infrared investigation of folding sepiolite
  22. First-principles study of sulfur isotope fractionation in pyrite-type disulfides
  23. Tetrataenite in terrestrial rock
  24. Thermo-compression of pyrope-grossular garnet solid solutions: Non-linear compositional dependence
  25. Phase relationships in the system K2CO3-CaCO3 at 6 GPa and 900–1450 °C
  26. Trace-element partitioning between plagioclase, alkali feldspar, Ti-magnetite, biotite, apatite, and evolved potassic liquids from Campi Flegrei (Southern Italy)
  27. Synthetic and natural ammonium-bearing tourmaline
  28. Anhydrite stability and the effect of Ca on the behavior of sulfur in felsic magmas
  29. Nuragheite, Th(MoO4)2·H2O, The Second Natural Thorium Molybdate And Its Relationships To Ichnusaite And Synthetic Th(MoO4)2†
  30. Structural Effects On Incorporated Water In Carbonated Apatites
  31. New Constraints On Electron-Beam Induced Halogen Migration In Apatite
  32. Origin Of The Lunar Highlands Mg-Suite: An Integrated Petrology, Geochemistry, Chronology, And Remote Sensing Perspective
  33. An In Situ High-Pressure Nmr Study Of Sodium Coordination Environment Compressibility In Albite Glass
  34. Hydrothermal Synthesis And Crystal Structure Of Also4(Oh): A Titanite-Group Member
  35. New Mineral Names
  36. Book Review: Thermal Remote Sensing Of Active Volcanoes: A User’S Manual
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