The initial steps of dissolution of gibbsite by salicylate were examined us
ing adsorption isotherms, electrophoresis, infrared spectroscopy, and contr
olled rate thermal analysis. A contact time of 24 h was chosen to avoid alt
eration of the gibbsite platelets. The results clearly show that adsorption
of salicylate takes place only on the edge faces of the gibbsite platelets
, where the OH groups are monocoordinated to Al atoms and bear a half charg
e. Monodentate and binuclear complexes are formed. The consequence is charg
e reversal on the solid surface. The dissolution rate is linearly correlate
d to the surface density of salicylate. These observations demonstrate that
dissolution occurs from the edge faces of the gibbsite platelets. Normaliz
ed dissolution rates should therefore be calculated using the surface area
of the edges of gibbsite and not the total surface area. (C) 2000 Elsevier
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