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Replacement and ion exchange reactions of scolecite in a high pH aqueous solution

Kristina G. Dunkel and Andrew Putnis
Replacement and ion exchange reactions of scolecite in a high pH aqueous solution
European Journal of Mineralogy (March 2014) 26 (1): 61-69

Abstract

The interaction of single crystals of a zeolite, scolecite (CaAl (sub 2) Si (sub 3) O (sub 10) .3H (sub 2) O), with NaCl and NaOH solutions of different concentrations and pH values was investigated in autoclaves at temperatures up to 200 degrees C. Only the experiments with 1 or 2 M NaOH at 200 degrees C led to significant reactions, namely one or two reaction rims, depending on the reaction time. The products were studied using electron microscopy, electron-microprobe analysis and X-ray diffraction. An inner reaction rim of mesolite (Na (sub 2) Ca (sub 2) Al (sub 6) Si (sub 9) O (sub 30) .8H (sub 2) O) was only observed in longer-term experiments. At all reaction times, however, a reaction rim consisting of Na,Al-substituted tobermorite 11 Aa (Ca (sub 4.5) Na (sub 1.3) Si (sub 5.2) Al (sub 1.0) O (sub 16) (OH) (sub 2) ) formed. The reaction interfaces are sharp, and the product phases form porous pseudomorphs of the original scolecite. Some advancements of the tobermorite rim are connected to fractures formed in the scolecite. Additional Cs exchange experiments (2 X 10 (super -4) M CsCl, 24 degrees C, 18 h) on the partly reacted samples showed that Cs-Na exchange in the tobermorite did not start simultaneously in the whole reaction rim, but only at the outer part. The results indicate that replacement of scolecite takes place by coupled dissolution-precipitation, independent of the similarity between the structure of scolecite and the reaction product. There is less fluid mobility around separate crystals in a solution than could be expected, which emphasises the importance of interfacial fluids. The infiltration of the fluid into the crystal partially depends on reaction-induced fracturing.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 26
Serial Issue: 1
Title: Replacement and ion exchange reactions of scolecite in a high pH aqueous solution
Affiliation: University of Muenster, Institut fuer Mineralogie, Munster, Germany
Pages: 61-69
Published: 201403
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 34
Accession Number: 2014-028687
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201418
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