TRANSFORMATION OF SYNTHETIC Zn-STEVENSITE TO Zn-TALC INDUCED BY THE HOFMANN-KLEMEN EFFECT

Stevensite-like sauconite, with the general composition: Si(4)(Zn(3-x)square(x))O(10)(OH)(2)R(2x)(+), where square is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li(+) and Zn(2+)) 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 degrees C, respectively, over 30 clays. X-ray diffraction (XRD) analysis confirmed that the samples synthesized were smectites. The number of vacant sites (x) per half unit cell (O(10)(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 Zn(2+)- saturated, and heated overnight at 300 degrees C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on NH(4)(+)-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: Si(4)Zn((3-x))Li(x)O(10)(OH)(2)NH(4x)(+), while after ZnHK treatment, it could be expressed as: Si(4)Zn(3)O(10)(OH)(2). Analysis by XRD and FTIR showed that the samples mooed from a Zn-stevensite-like structure to Zn-talc-likc structure after treatment with ZnHK. These results are interpreted as evidence that Zn(2+) (and Li(+)) migrated into the previously vacant sites under HK treatment.