EFFECT OF SALICYLATE ON DISSOLUTION OF COLLOIDAL ALUMINA PARTICLES

The interaction of chelate forming salicylic acid with alumina (bayeri te and boehmite) surfaces has been investigated at different pH and io nic strength. The adsorption of salicylate changes the adsorbent struc ture and strongly influences the aggregation stare of the aqueous disp ersions. Destructuring effect of salicylate on the adsorbents, similar to the weathering process in soils was observed, being more pronounce d for bayerite. Theoretical adsorption isotherms calculated on the bas is of the triple layer electrostatic adsorption model have strongly de viated form the experimental isotherms for the more soluble bayerite i n 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 c an 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 i s a function of pH and ionic strength. Weathering is likely to dominat e over the ionic strength effect. It is supposed that during weatherin g the Al-salicylate complexes weaken the neighbouring Al-O bonds in th e crystal lattice which results in loosening of the solid structure ne ar the surface. The latter effect has been detected by transmission el ectron microscopy.