| Abstract: |
Stevensite-like sauconite, with the general composition: Si (Znx , where is a vacant site, was synthesized. The objective was to study the possible migration of some cations (Li and Zn) within such trioctahedral smectites, under heating, following the so-called 'Hofmann-Klemen' (HK) effect. The initial gel wasdivided into five aliquotsand placed in teflon-coated hydrothermal reactorswith 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 (O(OH)) 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-saturated, and heated overnight at 300°C (HK treatment). Cation exchange capacity measurements were made by Fourier transform infrared spectroscopy (FTIR) on NH-saturated samples. After LiHK treatment, the structural formula of samples could be expressed as: SiZnLix1024x, while after ZnHK treatment, it could be expressed as: SiZnO(OH). 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 asevidence that Zn (and Li) migrated into the previously vacant sites under HK treatment. |
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