The interaction of chelate forming salicylic acid with alumina (bayerite and boehmite) surfaces has been investigated at different pH and ionic strength. The adsorption of salicylate changes the adsorbent structure and strongly influences the aggregation state of the aqueous dispersions. Destructuring effect of salicylate on the adsorbents, similar to the weathering process in soils was observed, being more pronounced for bayerite. Theoretical adsorption isotherms calculated on the basis of the triple layer electrostatic adsorption model have strongly deviated form the experimental isotherms for the more soluble bayerite in the whole concentration range, while qualitative agreement has been found between the model and experiment for the more stable boehmite at lower salicylate concentrations. As shown in literature, adsorption can be described by complex formation due to ligand exchange reactions with surface aluminum. On the other hand, the salicylate concentration near the solid surface depends on the electrostatic field, i.e., it is a function of pH and ionic strength. Weathering is likely to dominate over the ionic strength effect. It is supposed that during weathering the Al-salicylate complexes weaken the neighbouring Al-O bonds in the crystal lattice which results in loosening of the solid structure near the surface. The latter effect has been detected by transmission electron microscopy.
|Number of pages||11|
|Journal||ACH - Models in Chemistry|
|Publication status||Published - Dec 1 1997|
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