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

Abstract

The heterogeneous nucleation and growth of aluminum (oxy)hydroxide films in aqueous environments 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 AlCl 3 solutions was investigated as a function of pH using in situ X-ray reflectivity. The growth of well-ordered gibbsite films was observed at pH between 3 and 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. The gibbsite films formed on the muscovite surface dissolved more than two orders of magnitude faster than bulk gibbsite in pH 4 HCl solution, indicating that they can be described as a metastable phase. In contrast, no film growth was observed at pH between 9 and 12 where the solutions were supersaturated with respect to gibbsite. These results indicate that adsorption and accumulation of aqueous Al(III) species (i.e., Al 3+ and AlOH 2+ at acidic pH) is a critical step for the formation of secondary minerals on the negatively charged muscovite surface.

Epitaxial Growth of Gibbsite Sheets on the Basal Surface of Muscovite Mica

“…We infer that the laterally registered material grown in the present experiment is primarily gibbsite-like as surmised by Lee et al, 14,15 has its octahedra aligned with those of the substrate (in contrast to the alignment presented by Lee et al, 14 who could not determine this with specular data alone), is a single sheet thick, and contains antiphase domains, possibly coexisting with adsorbed Al ions, small oligomers and clusters, and/or Al atoms in a small fraction of the sheet vacancies. The atomic arrangements of domains A and B presented here (Figure S2) are spatially similar to those found in the interlayers of the Alchlorite minerals donbassite 43 and the "r" structure of cookeite.…”

Ion correlations drive charge overscreening and heterogeneous nucleation at solid–aqueous electrolyte interfaces

“…Here, the correlations between monovalent ions is enhanced at elevated ion concentration (i.e., low water content) near the highly charged surface. In natural waters, these ion–ion correlations are expected to be influenced by the presence of other ions, including hydronium and hydroxyl ions in acidic and alkaline solutions, via either competition for sorption sites on the mica surface or changes in ion speciation (e.g., ion pair formation and hydrolysis) in solutions ( 28 , 29 , 44 ). These interactions are expected to be more pronounced and more complex for multivalent cations due to stronger ion–ion correlations ( 2 – 4 ) and the increased role of ion hydration ( 5 – 8 ).…”

Aluminum Stress Induces Irreversible Proteomic Changes in the Roots of the Sensitive but Not the Tolerant Genotype of Triticale Seedlings

“…All minerals containing aluminum are insoluble at a neutral pH (6.5-7.0); hence, aluminum ions in such soils are biologically passive, non-available and thus non-harmful to plants. In acidic (pH 5.0-6.0) or very acidic (pH 4.0-5.5) soils, aluminum containing minerals can become soluble, releasing hydroxyl complexes of Al-ions in trivalent cationic forms, which are complexed in humus soils but picked up by plant roots from acidic sandy soils [1]. Since acidic soils constitute 30-40% of the world's arable land, with a constantly growing share due to anthropogenic impact, crop plants' aluminum tolerance is one of the features that affect higher/stable yielding in changing environments [2].…”