Surface charge characteristics of hydroxyaluminosilicate-clay complexes and reactivity with organic ligands

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The electric charge and surface characteristics of vermiculite or montmorillonite complexes with hydroxy-Al (HA) of hydroxyaluminosilicate (HAS) ions were studied in the pH range of 4 to 8. At pH 4 to 6, the negative charge of vermiculite or montmorillonite was drastically reduced by interlayer formation with HA or HAS ions. At pH 7 to 8, the magnitude of negative charge of these complexes was close to that of montmorillonite or vermiculite, suggesting that HAS or HA ions were excluded from the interlayer spaces of these clays. A significant positive charge was developed on HAS-montmorillonite complexes formed at NaOH/Al molar ratios of 2.0 and 2.5. The fixation of HAS or HA ions on montmorillonite or vermiculite caused significant reduction in total and internal surface areas but a slight increase in external surface area.Hydroxyaluminosilicate-clay complexes fixed a significant amount of phosphate on the interlayer and planar surfaces of these clays by ligand exchange. However, the complextion of HAS ions with vermiculite caused the significant reduction of K fixation.These data suggest that HAS and HA ions fixed on expansible 2:1 layer silicates contribute as active Al components to humus accumulation and phosphate retention in acidic and nonallophanic Andisols and related soils. Our data also indicate that the fixation of HAS and HA ions on 2:1 layer silicates can influence the levels of solution Al species that cause some toxicological problems in terrestrial and aquatic environments.