Of important interest to geochemical processes are the intercalation mechanisms controlling the physical exclusion of charged organic molecules including contaminants within the layers of smectite-type clay minerals. X-ray diffraction analyses imply pH-dependent interstratification but the underlying structures have not yet been resolved. Here, an annealing Monte-Carlo approach was employed to model the adsorption of a tetracycline antibiotic and Na ions within hydrated interlayers of a model montmorillonite and the thermodynamically-favorable geometric coordinates were used to simulate XRD profiles in order to unravel the interstratification patterns from the experimental data. The mixed layered crystals evolve from a random interstratification at low acidic pH to a segregated interstratification as pH increases whereby the theoretical layer stacking sequences illustrate an increased clustering of similar layer types with the exclusion of oxytetracycline intercalation from clay populations enriched in Na. This phenomenon has implications for the dynamics of organo-clay interactions in soils. .

Elucidating pH-dependent structures of interstratified layers in organic cation-smectite clay complexes

245th National Meeting (2013)

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