Hydrothermal synthesis, between 75 and 150°C, of high-charge, ferric nontronites

High-charge nontronites were synthesized at 75, 90, 100, 110, 125, and 150 degrees C from a silico-ferrous starting gel with Si(2)FeNa(2)O(6)center dot nH(2)O Composition. This gel was oxidized in contact with air and then hydrothermally treated, for a period of 4 weeks, under equilibrium water pressure. The synthesized nontronites were similar to each other, regardless of the synthesis temperature. Their structural formula, obtained from chemical analysis, X-ray diffraction (XRD), and Fourier transform infrared (FTIR), Mossbauer, and X-ray absorption fine structure spectroscopies is: (Si(3.25)Fe(0.75)(3+))Fe(2)(3+) O(10)(OH)(2)Na(0.75). A strictly ferric end-member of the nontronite series was therefore synthesized for the first time. The uncommon chemistry of the synthesized nontronites, notably the high level of Fe-for-Si substitution, induced particular XRD, FTIR, and differential thermal analysis-thermogravimetric analysis data. The ethylene glycol expandability of the synthetic nontronites was linked to their crystallinity and depended on the nature of the interlayer cation, moving from smectite to vermiculite-like behavior. As the synthesis temperature increased, the crystallinity of the synthesized clays increased. The nontronite obtained at 150 degrees C had the 'best crystallinity', which cannot be improved by increasing synthesis time or temperature.