Hydrothermal transformation of kaolinite to illite at 200 and 300^ºC

Abstract

The hydrothermal reaction of kaolinite in the system Na2O-K2O-(MgO)-Al2O3-SiO2- H2O has been investigated at 200 and 300ºC. The study of the solid products indicates that, at 200ºC, disordered illite was the first phase formed, which evolved at increasing run times towards well ordered illite and analcime. After longer reaction times illite and kaolinite were the sole phases identified by XRD. The b parameter of the illites increased at longer reaction times, from 9.05 to 9.08 Å. Study by TEM/AEM revealed the presence of surface chlorite-like layers, covering the illite packets, however. The trend observed in the products of the reaction at 300ºC was similar, except for the presence of boehmite or pseudoboehmite at the higher temperature. The values of the bparameter of illite, of the order of 9.12 –9.16 Å, indicate that illites formed at 300ºC have a more trioctahedral character. The results obtained also indicate that Mg determines which product will be formed, Kand Na-zeolites and Al-rich illites being the phases formed in the absence of Mg.

Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle Toarcian in the Paris Basin

“…On the Paris Basin borders, the ~2 km burial depth and the very low thermal maturity of the organic matter suggest unsubstantial to moderate illitisation and chloritisation (Debrabant et al, 1992;Delavenna et al, 1989). If these burial temperatures may introduce discrete diagenesis as illitisation of smectite-rich clay minerals (Lanson et al, 2009), they cannot affect kaolinite, whose dissolution and transformation into illite occurs at higher temperatures (Bentablo et al, 2003;Chamley, 1989;Lanson et al, 2002;Mantovani et al, 2010). The absence of direct control of the lithology on the kaolinite content is supplementary evidence that diagenesis and fluids have not significantly affected the primary signature of clay minerals.…”

Characterization of the expandable clays formed from kaolinite at 200ºC

“…Accordingly, the kaolinite to K-mica transformation was observed in laboratory experiments, reacting kaolinite with alkaline solutions (e.g. Huang, 1993;Bauer et al, 1998;Bentabol et al, 2003a) or through the formation of serpentine-like phases, which reacted with KCl to form dioctahedral mica (Frank-Kamenetskii et al, 1990). The formation of Nabearing phases from kaolinite has also been studied (e.g.…”

Evaluation of rare earth on layered silicates under subcritical conditions: Effect of the framework and interlayer space composition

“…1b) did not alter the structure, crystallinity, or the collapsed state of the layers, which maintained the basal spacing of the starting material. The emergence of a new reflection at 14.6 º 2θ was observed in the XRD pattern corresponding to boehmite (PDF 76-1871), which was previously observed as a product of hydrothermal treatment of pyrophyllite under aqueous acidic conditions at 300ºC (Alba et al, 2010), thus indicating that this structure shows some stability under hydrothermal conditions (Bentabol et al, 2003). The whole set of reflections for the Lu 2 Si 2 O 7 phase was also evident alongside some minor reflections for the H 2 Si 2 O 5 phase.…”