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Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy

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Published/Copyright: April 1, 2015
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American Mineralogist
From the journal American Mineralogist Volume 92 Issue 4

Abstract

The local structural environments in a series of natural and synthetic alunite samples [ideally AAl3(SO4)2(OH)6, A = H3O+, D3O+, Na+, and K+] have been probed by solid-state 1H, 2H, 23Na, 27Al, and 39K NMR spectroscopy. The natural alunite [KAl3(SO4)2(OH)6] and synthetic hydronium alunite samples contain few structural defects, whereas the synthetic natroalunite and alunite samples have ca. 10% Al vacancies based on 27Al NMR. A new 27Al local environment (AlD) was observed and assigned to Al with one Al vacancy in the first cation sphere. Three different proton environments, Al2-OH, Al - OH2, and H3O+ are detected by 1H and 2H MAS NMR. The hydronium ion (H3O+) is only observed in hydronium alunite, and is associated with the stoichiometric regions of the sample. It was not detected in 1H and 2H NMR spectra of alunite and natroalunite despite K (Na) occupancies of significantly less than 100%, as determined from elemental analysis. Thus, our NMR results suggest that the common assumption, namely that an A vacancy and an Al3+ vacancy are compensated by adding an H3O+and 3H+ (creating 3 Al-OH2 groups), respectively, is too simplistic. Instead, a significant fraction of the Al3+ vacancies are compensated for by 4 H+ ions, resulting in 4 Al-OH2 groups per vacancy. This substitution is accompanied by the simultaneous deprotonation of a H3O+ ion present on the A site. The resultant H2O molecule is unnecessary for charge balance, accounting for the A-site deficiency often observed. The presence of Al3+ and A+ vacancies appears closely correlated based on NMR.

Keywords: Alunite; solid-state NMR; hydronium ion; 23Na NMR; 27Al NMR; 1H NMR; 2H NMR; 39K NMR
Received: 2006-8-9
Accepted: 2006-11-14
Published Online: 2015-4-1
Published in Print: 2007-4-1

© 2015 by Walter de Gruyter Berlin/Boston

Articles in the same Issue

  1. New constraints on metamorphic history of Adirondack diopsides (New York, U.S.A.): Al and δ18O profiles
  2. Hammadah al Hamra 193: The first amphibole-bearing winonaite
  3. Crystal chemistry of trioctahedral micas in alkaline and subalkaline volcanic rocks: A case study from Mt. Sassetto (Tolfa district, Latium, central Italy)
  4. Magnetic excitations and heat capacity of fayalite, Fe2SiO4
  5. The barometer tremolite + tschermakite + 2 albite = 2 pargasite + 8 quartz: Constraints from experimental data at unit silica activity, with application to garnet-free natural assemblages
  6. In-situ measurement of dissolution of anorthite in Na-Cl-OH solutions at 22 °C using phase-shift interferometry
  7. Experimental investigation of the breakdown of dolomite in rock cores at 100 MPa, 650-750 °C
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  12. Heat-pulse calorimetry measurements on natural chlorite-group minerals
  13. Low-temperature behavior of NaGaSi2O6
  14. Single-crystal elasticity of zoisite Ca2Al3Si3O12(OH) by Brillouin scattering
  15. The effect of valence state and site geometry on Ti L3,2 and O K electron energy-loss spectra of TixOy phases
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  23. Rhombohedral (9R) and hexagonal (6H) perovskites in barium silicates under high pressure
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  25. Neptunium incorporation in sodium-substituted metaschoepite
  26. The effect of H2O on olivine crystallization in MORB: Experimental calibration at 200 MPa
  27. Symmetry and crystal structure of biaxial elbaite-liddicoatite tourmaline from the Transbaikalia region, Russia
  28. Letter: Onion morphology and microstructure of polyhedral serpentine
  29. Letter: Ion microprobe analysis of (231Pa)/(235U) and an appraisal of protactinium partitioning in igneous zircon
  30. Letter: Structural investigation of Mg local environments in silicate glasses by ultra-high field 25Mg 3QMAS NMR spectroscopy
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https://doi.org/10.2138/am.2007.2414
Keywords for this article
Alunite; solid-state NMR; hydronium ion; 23Na NMR; 27Al NMR; 1H NMR; 2H NMR; 39K NMR

Articles in the same Issue

  1. New constraints on metamorphic history of Adirondack diopsides (New York, U.S.A.): Al and δ18O profiles
  2. Hammadah al Hamra 193: The first amphibole-bearing winonaite
  3. Crystal chemistry of trioctahedral micas in alkaline and subalkaline volcanic rocks: A case study from Mt. Sassetto (Tolfa district, Latium, central Italy)
  4. Magnetic excitations and heat capacity of fayalite, Fe2SiO4
  5. The barometer tremolite + tschermakite + 2 albite = 2 pargasite + 8 quartz: Constraints from experimental data at unit silica activity, with application to garnet-free natural assemblages
  6. In-situ measurement of dissolution of anorthite in Na-Cl-OH solutions at 22 °C using phase-shift interferometry
  7. Experimental investigation of the breakdown of dolomite in rock cores at 100 MPa, 650-750 °C
  8. Dissolution of the (001) surface of galena: An in situ assessment of surface speciation by fluid-cell micro-Raman spectroscopy
  9. An infrared spectroscopic study of the OH stretching frequencies of talc and 10-Å phase to 10 GPa
  10. Co2+-Cu2+ substitution in bieberite solid-solution series, (Co1-xCux)SO4·7H2O, 0.00 ≤ x ≤ 0.46: Synthesis, single-crystal structure analysis, and optical spectroscopy
  11. Clinoenstatite exsolution in diopsidic augite of Dabieshan: Garnet peridotite from depth of 300 km
  12. Heat-pulse calorimetry measurements on natural chlorite-group minerals
  13. Low-temperature behavior of NaGaSi2O6
  14. Single-crystal elasticity of zoisite Ca2Al3Si3O12(OH) by Brillouin scattering
  15. The effect of valence state and site geometry on Ti L3,2 and O K electron energy-loss spectra of TixOy phases
  16. Characterization of defects and the local structure in natural and synthetic alunite (K, Na, H3O)Al3(SO4)2(OH)6 by multi-nuclear solid-state NMR spectroscopy
  17. Using a mineral lifetime diagram to evaluate the persistence of olivine on Mars
  18. Complexity in 15- and 30-sectors polygonal serpentine: Longitudinal sections, intrasector stacking faults and XRPD satellites
  19. Light-induced alteration of arsenic sulfides: A new product with an orthorhombic crystal structure
  20. Transmission electron microscopy study of magnetites in a freshwater population of magnetotactic bacteria
  21. Anomalous behavior at the I2/a to Imab phase transition in SiO2-moganite: An analysis using hard-mode Raman spectroscopy
  22. The system Ag-Au-Se: Phase relations below 405 K and determination of standard thermodynamic properties of selenides by solid-state galvanic cell technique
  23. Rhombohedral (9R) and hexagonal (6H) perovskites in barium silicates under high pressure
  24. Structural effects of pressure on monoclinic chlorite: A single-crystal study
  25. Neptunium incorporation in sodium-substituted metaschoepite
  26. The effect of H2O on olivine crystallization in MORB: Experimental calibration at 200 MPa
  27. Symmetry and crystal structure of biaxial elbaite-liddicoatite tourmaline from the Transbaikalia region, Russia
  28. Letter: Onion morphology and microstructure of polyhedral serpentine
  29. Letter: Ion microprobe analysis of (231Pa)/(235U) and an appraisal of protactinium partitioning in igneous zircon
  30. Letter: Structural investigation of Mg local environments in silicate glasses by ultra-high field 25Mg 3QMAS NMR spectroscopy
  31. Letter: Entropies of mixing and subsolidus phase relations of forsterite–fayalite (Mg2SiO4–Fe2SiO4) solid solution
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