Effect of pH on the Formation of Gibbsite-Layer Films at the Muscovite (001)−Water Interface


Effect of pH on the Formation of Gibbsite-Layer Films at the Muscovite (001)−Water Interface

Lee, S. S.; Schmidt, M.; Sturchio, N. C.; Nagy, K. L.; Fenter, P.

Aluminum (oxy)hydroxide films play an important role as sorbents of toxic elements in aqueous environments, where their heterogeneous nucleation and growth can be controlled by the speciation of dissolved Al species and the charge and structure of underlying mineral surfaces. The structure of gibbsite films nucleated at the interface between the muscovite (001) surface and 1 mM AlCl3 solutions was investigated as a function of pH using in situ X-ray reflectivity. Growth of well-ordered gibbsite films was observed at pH 3–4, even when the solutions were undersaturated with respect to gibbsite. The ordering of these gibbsite films likely resulted from the structural similarity (i.e., epitaxy) between the basal planes of gibbsite and muscovite. In contrast, no film growth was observed at pH 9–12 where the solutions were supersaturated with respect to gibbsite. These results indicate that adsorption and accumulation of aqueous Al(III) species (i.e., Al3+ and AlOH2+ at acidic pH) is a critical step for the formation of secondary minerals on the negatively-charged muscovite surface.

Keywords: Mica, Nucleation, Epitaxy; AFM; CTR/RAXR; X-ray Reflectivity

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Publ.-Id: 28458