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Clays and Clay Minerals; December 2008; v. 56; no. 6; p. 645-654; DOI: 10.1346/CCMN.2008.0560605
© 2008 Clay Minerals Society
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TRANSFORMATION OF SYNTHETIC Zn-STEVENSITE TO Zn-TALC INDUCED BY THE HOFMANN-KLEMEN EFFECT

S. Petit*, D. Righi and A. Decarreau

Université de Poitiers, FRE3114 CNRS, HydrASA, 40 Avenue du Recteur Pineau, F-86022 POITIERS Cedex, France

* E-mail address of corresponding author: Sabine.Petit{at}univ-poitiers.fr

Stevensite-like sauconite, with the general composition: Si4(Zn3–x{square}x)O10(OH)2R2x+, where is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li+ and Zn2+) within such trioctahedral smectites, under heating, following the so-called ‘Hofmann-Klemen’ (HK) effect. The initial gel was divided into five aliquots and placed in teflon-coated hydrothermal reactors with distilled water, and these were hydrothermally treated at 80, 100, 120, 150, and 200°C, respectively, over 30 days. X-ray diffraction (XRD) analysis confirmed that the samples synthesized were smectites. The number of vacant sites (x) per half unit cell (O10(OH)2) ranged from nearly 0 to 0.23 but no simple relationship was established between x and the temperature of synthesis. The samples were Li+- and Zn2+-saturated, and heated overnight at 300°C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on NH4+-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: Si4Zn(3–x)LixO10(OH)2NH4x+, while after ZnHK treatment, it could be expressed as: Si4Zn3O10(OH)2. Analysis by XRD and FTIR showed that the samples moved from a Zn-stevensite-like structure to Zn-talc-like structure after treatment with ZnHK. These results are interpreted as evidence that Zn2+ (and Li+) migrated into the previously vacant sites under HK treatment.

Key Words: Cation Exchange Capacity • Hofmann-Klemen • Kerolite • Li+ • NH4+ • Octahedral Charge • Sauconite • Smectite • Stevensite • Synthesis • Zinc






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