Studies of the Solid/Solution "Interfacial" Dealumination of Kaolinite in HCl(aq) Using Solid-State 1H CRAMPS and SP/MAS 29Si NMR Spectroscopy
详细信息 查看全文
- 作者：John J. Fitzgerald ; Abdullatef I. Hamza ; Charles E. Bronnimann ; and Steven F. Dec
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：July 30, 1997
- 年：1997
- 卷：119
- 期：30
- 页码：7105 - 7113
- 全文大小：296K
- 年卷期：v.119,no.30(July 30, 1997)
- ISSN：1520-5126
文摘
The dealumination of kaolinite by the solid/solution"interfacial" reaction with HCl(aq) at 98 
Cwasinvestigated using solid-state 1H CRAMPS and MAS29Si NMR techniques. The single-pulse (SP)/MAS29Si NMRspectra of kaolinite-derived solids that are 2-83% dealuminated areobserved to be dependent upon the degree ofdealumination, showing three resolvable resonances at -89, -100,and -109 ppm. The -89 ppm resonance is dueto silicon Q3-typeSi(OSi)3(OAl2) sites in unreactedkaolinite, while the latter two resonances are assigned tonewQ3-type silica-alumina (Si-OH+-Al) andto Q4-type amorphous silica (Si(OSi)4)sites contained in dealuminatedkaolinite solids following partial dealumination. The1H CRAMPS spectra of these dealuminated solids arealsodependent upon the degree of removal of Al3+ ions fromthe kaolinite Al-OH-Al layer. In addition to abroadproton peak at 4.0 ppm due to structural protons of the intactAl-OH-Al layer in unreacted kaolinite, two newresonances at 0.4 and 7.0 ppm are assigned to protons of the newsilanol (Si-OH) and alumina-silica(Si-OH+-Al) sites. The spectral intensities of the SP/MAS29Si and 1H CRAMPS NMR results arecorrelated with the progressof dealumination, permitting the development of a structural model forpartially dealuminated kaolinite. This structuralmodel is consistent with a kinetic model involving achemically-controlled "heterogeneous" reaction processwherebyH+ ion attack of the Si-O-Al linkages at the edges ofthe mineral surface leads to liberation of aluminum ionsintothe solution medium.
Cwasinvestigated using solid-state 1H CRAMPS and MAS29Si NMR techniques. The single-pulse (SP)/MAS29Si NMRspectra of kaolinite-derived solids that are 2-83% dealuminated areobserved to be dependent upon the degree ofdealumination, showing three resolvable resonances at -89, -100,and -109 ppm. The -89 ppm resonance is dueto silicon Q3-typeSi(OSi)3(OAl2) sites in unreactedkaolinite, while the latter two resonances are assigned tonewQ3-type silica-alumina (Si-OH+-Al) andto Q4-type amorphous silica (Si(OSi)4)sites contained in dealuminatedkaolinite solids following partial dealumination. The1H CRAMPS spectra of these dealuminated solids arealsodependent upon the degree of removal of Al3+ ions fromthe kaolinite Al-OH-Al layer. In addition to abroadproton peak at 4.0 ppm due to structural protons of the intactAl-OH-Al layer in unreacted kaolinite, two newresonances at 0.4 and 7.0 ppm are assigned to protons of the newsilanol (Si-OH) and alumina-silica(Si-OH+-Al) sites. The spectral intensities of the SP/MAS29Si and 1H CRAMPS NMR results arecorrelated with the progressof dealumination, permitting the development of a structural model forpartially dealuminated kaolinite. This structuralmodel is consistent with a kinetic model involving achemically-controlled "heterogeneous" reaction processwherebyH+ ion attack of the Si-O-Al linkages at the edges ofthe mineral surface leads to liberation of aluminum ionsintothe solution medium.