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Hydrothermal Crystallization of Ammonium-Saponite at 200 °C and Autogenous Water Pressure

Published online by Cambridge University Press:  28 February 2024

Roland J. M. J. Vogels ,
Johan Breukelaar ,
J. Theo Kloprogge ,
J. Ben H. Jansen  and
John W. Geus
Roland J. M. J. Vogels
Affiliation:
Department of Inorganic Chemistry, University of Utrecht, P.O. Box 80.083, 3508 TB Utrecht, The Netherlands
Johan Breukelaar
Affiliation:
SRTCA (Shell Research B.V.), P.O. Box 38000, 1030 BN Amsterdam, The Netherlands
J. Theo Kloprogge*
Affiliation:
TNO-Institute of Applied Physics-TU Delft, Department of Inorganic Materials Chemistry, P.O. Box 595, 5600 AN Eindhoven, The Netherlands
J. Ben H. Jansen
Affiliation:
Bowagemi, Prinses Beatrixlaan 20, 3972 AN Driebergen, The Netherlands
John W. Geus
Affiliation:
Department of Inorganic Chemistry, University of Utrecht, P.O. Box 80.083, 3508 TB Utrecht, The Netherlands
*
‡Current address: Hoevenbos 299, 2716 Zoetermeer, The Netherlands.
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Abstract

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The effects of reaction time (2 to 72 h) and NH4+/A13+ molar ratio (1.6, 2.4 and 3.2) on the hydrothermal synthesis of ammonium-saponites are investigated. The gels are obtained by mixing powders, resulting in a stoichiometric composition, Mg3Si34Al0.6O10(OH)2, with aqueous ammonium solutions, with and without F, to result in initial NH4+/Al3+ molar ratios of 1.6, 2.4 and 3.2. The solid bulk products are characterized by X-raydiffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) analysis. The cation exchange capacity (CEC) is determined with an ammonia selective electrode and the pH of the water from the first washing is measured. Ammonium-saponite is formed rapidly within 16 h. A higher NH4+/A13+ molar ratio and the presence of F facilitate the crystallization of saponite. Small metastable amounts of bayerite, Al(OH)3, are present at low NH4+/A13+ molar ratios; after short reaction times, they disappear. During the first 4 h, the pH decreases rapidly, then drops slowly to a constant level of approximately 4.6 after 60 h. With increasing reaction time, saponite crystallites grow in the ab directions of the individual sheets with almost no stacking to thicker flakes. The NH4+ CEC of the solid products increases strongly within the first 24 h. A maximum of 53.3 meq/100 g is observed. The saponite yield increases from approximately 25% after 2 h to almost 100% after 72 h.

Keywords

Cation Exchange CapacitySaponiteSynthesisX-ray DiffractionX-ray Fluorescence
Type
Research Article
Information
Clays and Clay Minerals , Volume 45 , Issue 1 , February 1997 , pp. 1 - 7
Copyright
Copyright © 1997, The Clay Minerals Society

Footnotes

†

This paper is a joint contribution from the Debye Institute, Utrecht, and Shell Research B.V., Amsterdam, The Netherlands.

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