Hydrothermal (200°C) synthesis and crystal chemistry of iron-rich kaolinites

In order to study Al-Fe substitution, Fe-kaolinites were synthesized at 200°C from glasses (Si/(Al + Fe) = 1) with varying Fe content. XRD and IR spectroscopy showed that kaolinites with increasing Fe contents could be synthesized, and Mössbauer spectroscopy indicated that the iron is strictly ferric. Chemical analyses (STEM) of kaolinite particles determined up to almost 7% Fe 2 O 3 , which probably does not represent a structural limit. The effect of Fe 3+ content is evident on growth kinetics and particle size of kaolinites, both decreasing with % Fe 2 O 3 . However, it is not possible to establish a general correlation between Fe content and percentage of structural defects. Acccording to IR spectroscopy, some synthesized Fe-rich kaolinites can have relatively good crystallinity.