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Iron-bearing kaolinite in Venezuelan laterites: I. Infrared spectroscopy and chemical dissolution evidence

Published online by Cambridge University Press:  09 July 2018

E. Mendelovici
Affiliation:
Laboratorio de Fisico-Quimica de Materiales, CIC, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 1827, Caracas, Venezuela
Sh. Yariv
Affiliation:
Laboratorio de Fisico-Quimica de Materiales, CIC, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 1827, Caracas, Venezuela
R. Villalba
Affiliation:
Laboratorio de Fisico-Quimica de Materiales, CIC, Instituto Venezolano de Investigaciones Científicas IVIC, Apartado 1827, Caracas, Venezuela

Abstract

Fe substitution for Al in kaolinite (from Venezuelan laterites) is proved by infrared spectroscopy and chemical techniques. The location of Fe in the octahedral sheet is characterized by two absorption bands, at 865–875 and 3607 cm−1, assigned as δ Al-OH-Fe and v OH respectively. The detection of the 865 cm−1 band requires the use of CsCl for the preparation of the disks heated to 270°C so that the clay delaminates as a result of a kaolinite-CsCl-H2O complex formation. The 3607 cm−1 absorption is detected when KI disks are prepared. These two characteristic frequencies persist after either thermal decomposition or selective chemical dissolution of free iron and aluminium hydroxides.

Selective chemical dissolutions by consecutive treatments for; (1) the removal of free iron oxides, (2) gibbsite removal and (3) extractions of Fe and Al from kaolinite, give additional evidence about the occurrence of this solid solution.

Résumé

Résumé

La substitution de fer à l'aluminum dans la kaolinite (de latérites du Vénézuéla) a été étudiée par des techniques de spectroscopie infrarouge et chimiques. La position de Fe dans la feuille octaédrique est caractérisée par deux bandes d'absorption, à 865–875 et à 3607 cm−1, attribuées respectivement à δ Al-OH-Fe et à v OH. La détection de la bande à 865 cm−1 nécessite l'emploi de CsCl dans la préparation des disques chauffés à 270°C afin que les couches d'argile se séparent comme conséquence de la formation d'un complexe kaolinite-CsCl-H2O. L'absorption à 3067 cm−1 est détectée lorsqu'on prépare des disques KI. Ces deux fréquences caractéristiques persistent aussi bien après décomposition thermique qu'après dissolution chimique sélective des hydroxydes libres de fer et d'aluminium.

Les dissolutions thermiques sélectives par traitements successifs pour: (1) l'élimination des oxydes de fer libres, (2) l'élimination de la gibbsite et (3) l'extraction de Fe et de Al de la kaolinite, apportent une preuve supplémentaire de l'existence de cette solution solide.

Kurzreferat

Kurzreferat

Die Substitution von Fe für Al im Kaolinit (von venezuelanischen Lateriten) wird durch Infrarot-Spektroskopie und chemische Verfahren nachgewiesen. Die Lage des Fe in der Oktaederschicht ist durch zwei Absorptionsbänder, bei 865–875 und 3607 cm−1 bekennzeichnet, und diese sind als δ Al-OH-Fe bzw. v OH bestimmt. Der Nachweis des 865 cm−1-Bandes setzt die Verwendung von CsCl zur Präparierung der auf 270°C erhitzten Scheiben voraus, so daß infolge des Entstehens eines Kaolinit-CsCl-H2O-Komplexes Schichtspaltung in dem Ton auftritt. Die 3607 cm−1-Absorption wird bei Präparierung von KI-Scheiben nachgewiesen. Diese beiden charakteristischen Frequenzen bestehen auch noch nach thermischem Abbau oder nach selektiver chemischer Auflösung von ungebundenen Eisen- und Aluminiumhydroxiden.

Selektive chemische Auflösung durch aufeinanderfolgende Behandlungen (1) zur Absonderung freier Eisenoxide, (2) Abscheidung des Gibbsits und (3) Extraktion von Fe und Al aus Kaolinit bieten weitere Beweise für das Vorkommen dieser festen Lösung.

Resumen

Resumen

La sustitución de Al por Fe en la caolinita (procedente de lateritas venezolanas) es demonstrada por técnicas de espectroscopia de infrarrojos y químicas. La ubicación de Fe en la lámina octaédrica se caracteriza por dos bandas de absorción, a 865–875 y 3607 cm−1, asignadas como δ Al-OH-Fe y v OH respectivamente. La detección de la banda de 865 cm−1 exige el uso de CsCl para la preparación de los discos calentados a 270°C para que la arcilla se exfolie como resultado de la formación de un complejo caolinita-CsCl-H2O. La absorción a 3607 cm−1 se detecta cuando se preparan discos de KI. Estas dos frecuencias características persisten después, bien por descomposición térmica o bien por disolución química selectiva de hidróxidos de hierro y aluminio.

Las disoluciones químicas selectivas mediante tratamientos consecutivos para: (1) la eliminación de óxidos de hierro libres, (2) la eliminación de gibbsita y (3) las extracciones de Fe y Al de la caolinita, proporcionan evidencia adicional de la presencia de esta solución sólida.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1979

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