Characteristics of Granular Boehmite and Its Ability to Adsorb Phosphate from Aqueous Solution

Abstract

In this study, we investigated the surface properties of granulated boehmite with vinyl acetate (G-BE20) and measured the amount of phosphate it adsorbed and the effect of contact time and solution pH on the adsorption process. The specific surface area (144.9 m(2)/g) and the number of surface hydroxyl groups (0.88 mmol/g) of G-BE20 were smaller than those of virgin boehmite (BE), which gave a specific surface area and number of surface hydroxyl groups of 297.0 m(2)/g and 1.08 mmol/g, respectively. The amount of phosphate adsorbed increased with the temperature. The isotherm model of Langmuir was used to fit experimental adsorption equilibrium data for phosphate adsorption onto G-BE20. The calculated thermodynamic parameters show the spontaneous and endothermic nature of the adsorption process. The equilibrium adsorption onto G-BE20 was reached within 16 h and the amount of phosphate adsorbed was 8.4 mg/g. The kinetic mechanism of phosphate uptake was evaluated with two different models: the Largergren pseudo first- and pseudo second-order models. The data obtained showed a better fit to the pseudo second-order model (0.991) than to the pseudo first-order model (0.967), as indicated by the r values. The rate constants for the adsorption of phosphate onto G-BE20 were calculated as 0.481 1/h and 0.029 g/mg h. The adsorption of phosphate onto G-BE20 was the maximum in the pH range 3.0-4.0.