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Structural Fluorine in Sepiolite

Published online by Cambridge University Press:  02 April 2024

Julio Santaren ,
Jesus Sanz  and
Eduardo Ruiz-Hitzky
Julio Santaren
Affiliation:
Research and Development Department, Tolsa, S.A., P.O. Box 38017, 28080 Madrid, Spain
Jesus Sanz
Affiliation:
Instituto de Ciencia de Materiales, C.S.I.C., Serrano 115 bis, 28006 Madrid, Spain
Eduardo Ruiz-Hitzky
Affiliation:
Instituto de Ciencia de Materiales, C.S.I.C., Serrano 115 bis, 28006 Madrid, Spain
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Abstract

Sepiolite from Vallecas-Vicálvaro, Spain, contains 1.3% fluorine. Laser microprobe mass spectrometry of this sepiolite suggests the presence of fragments of (SiO2)nOMgF and (SiO2)nOMgOH, which are typical of the sepiolite structure. During thermal dehydroxylation, the fluorine in this sepiolite is removed simultaneously with OH groups at about 750°C. Nuclear magnetic resonance spectroscopy (NMR) of 19F indicates that the fluorine is located in the interior of the sepiolite structure, probably substituting for OH groups, and is homogeneously distributed. In the Vallecas-Vicálvaro sepiolite, about one of every four OH groups bound to Mg2+ is substituted by fluorine. The kinetics of extraction of Mg2+ and F- ions by acid treatment (1 N HCl) shows a more rapid extraction of Mg2+, with a monotonous decrease of the Mg/F ratio as the extent of extraction increases. These results support the internal location of the fluorine, as suggested by the NMR data.

Keywords

FluorineHydroxylLaser microprobe mass spectrometryDissolutionNuclear magnetic resonanceSepiolite
Type
Research Article
Information
Clays and Clay Minerals , Volume 38 , Issue 1 , February 1990 , pp. 63 - 68
Copyright
Copyright © 1990, The Clay Minerals Society

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