Structural changes of allophane during purification procedures as determined by solid-state 27A1 and 29Si NMR

Research output: Contribution to journalArticle

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Abstract

Allophanes are poorly crystalline and quasi-stable aluminosilicate minerals, the structures of which are sensitive to chemical treatment. In the present study, solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectra of allophane samples were monitored as they went through several purification procedures. It was confirmed that no significant structural changes were caused by boiling with 6% H2O2 to remove organic matter, by size fractionation (sonification), by sedimentation, by precipitation at pH 4.0, or by dithionite-citrate-bicarbonate treatment for the removal of Fe (hydr)oxides. Hot 5% Na2CO3 treatment for the removal of reactive silica-alumina gels and adsorbed citrate from allophane samples, however, decreased signal intensity corresponding to imogolite-like Si (Q33VIAl, -78 ppm in 29Si NMR) and increased signal intensities corresponding to IVAl (55 ppm in 27Al NMR) and possibly X-ray amorphous aluminosilicates (centered at -85 ppm in 29Si NMR). Cold (room temperature) 5% Na2CO3 treatment for 16 h proved to be effective in avoiding these structural changes.

Original languageEnglish
Pages (from-to)653-658
Number of pages6
JournalClays and Clay Minerals
Volume53
Issue number6
DOIs
Publication statusPublished - Dec 1 2005
Externally publishedYes

Fingerprint

allophane
structural change
Purification
purification
nuclear magnetic resonance
nuclear magnetic resonance spectroscopy
Nuclear magnetic resonance
aluminosilicate
Citric Acid
citrates
imogolite
Dithionite
aluminum oxide
Aluminum Oxide
chemical treatment
Fractionation
Bicarbonates
boiling
bicarbonates
Sedimentation

All Science Journal Classification (ASJC) codes

  • Soil Science
  • Earth and Planetary Sciences (miscellaneous)
  • Geochemistry and Petrology
  • Water Science and Technology

Cite this

Structural changes of allophane during purification procedures as determined by solid-state 27A1 and 29Si NMR. / Hiradate, Syuntaro.

In: Clays and Clay Minerals, Vol. 53, No. 6, 01.12.2005, p. 653-658.

Research output: Contribution to journalArticle

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abstract = "Allophanes are poorly crystalline and quasi-stable aluminosilicate minerals, the structures of which are sensitive to chemical treatment. In the present study, solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectra of allophane samples were monitored as they went through several purification procedures. It was confirmed that no significant structural changes were caused by boiling with 6{\%} H2O2 to remove organic matter, by size fractionation (sonification), by sedimentation, by precipitation at pH 4.0, or by dithionite-citrate-bicarbonate treatment for the removal of Fe (hydr)oxides. Hot 5{\%} Na2CO3 treatment for the removal of reactive silica-alumina gels and adsorbed citrate from allophane samples, however, decreased signal intensity corresponding to imogolite-like Si (Q33VIAl, -78 ppm in 29Si NMR) and increased signal intensities corresponding to IVAl (55 ppm in 27Al NMR) and possibly X-ray amorphous aluminosilicates (centered at -85 ppm in 29Si NMR). Cold (room temperature) 5{\%} Na2CO3 treatment for 16 h proved to be effective in avoiding these structural changes.",
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AB - Allophanes are poorly crystalline and quasi-stable aluminosilicate minerals, the structures of which are sensitive to chemical treatment. In the present study, solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectra of allophane samples were monitored as they went through several purification procedures. It was confirmed that no significant structural changes were caused by boiling with 6% H2O2 to remove organic matter, by size fractionation (sonification), by sedimentation, by precipitation at pH 4.0, or by dithionite-citrate-bicarbonate treatment for the removal of Fe (hydr)oxides. Hot 5% Na2CO3 treatment for the removal of reactive silica-alumina gels and adsorbed citrate from allophane samples, however, decreased signal intensity corresponding to imogolite-like Si (Q33VIAl, -78 ppm in 29Si NMR) and increased signal intensities corresponding to IVAl (55 ppm in 27Al NMR) and possibly X-ray amorphous aluminosilicates (centered at -85 ppm in 29Si NMR). Cold (room temperature) 5% Na2CO3 treatment for 16 h proved to be effective in avoiding these structural changes.

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