Kinetics and adsorption behaviour of salicylate on α-alumina in aqueous medium

The adsorption of salicylate on α-alumina was studied in aqueous medium over the pH range 4–9. Kinetics of adsorption of salicylate on α-alumina was studied at pH 5 and 25, 30 and 40 °C. The state of equilibrium was obtained after 2.5 h. The adsorption density of salicylate on α-alumina increases with the increase of temperature due to increase in surface loading and decreases with the increase of pH and ionic strength of the system. The decrease in adsorption density is attributed to decrease of the positive surface charge and the double layer thickness. The rate constant for adsorption of salicylate on α-alumina was found to increase with the increase in temperature and the thermodynamic parameters were estimated. The FTIR spectra of salicylate after adsorption on the α-alumina surfaces were recorded for obtaining the bonding properties of salicylate. The phenolic group is not deprotonated as evident by the presence of the characteristic band at 1266 cm−1. The shifting of the characteristics peak frequencies of COO− and appearance of a new band at ≈1710 cm−1 due to >CO indicate that the salicylate is coordinated monodentally with respect to the carboxyl group.