Adsorption of Pt(IV) and Pd(II) by calcined dried aluminum hydroxide gel from aqueous solution system

Abstract

In this study, calcined dried aluminum hydroxide gels (Gs) were prepared at 300–1000°C (G300–G1000) as adsorbents. The properties of the adsorbents (i.e., XRD patterns, SEM images, specific surface areas, and number of hydroxyl groups) were investigated. The adsorption of Pt(IV) and Pd(II) onto Gs at different temperatures was evaluated. Calcination transformed virgin G into γ- and α-alumina. G600 had the largest specific surface area (107.2m2/g) and number of hydroxyl groups (1.12mmol/g) of the Gs. G600 also adsorbed the greatest amount of Pt(IV) and Pd(II). The amount of Pt(IV) and Pd(II) adsorbed was more closely related to the number of hydroxyl groups than the specific surface area. The adsorption mechanism of Pt(IV) and Pd(II) onto G600 mainly involved ion exchanges. The optimal pH for the adsorption of Pt(IV) and Pd(II) onto G600 was ∼5.0, which suggests that [PtCl5(OH)]2− and [PdCl3(OH)]2− species are suitable for adsorption. Pt(IV) and Pd(II) compete with chloride ions for adsorption sites on G600 in the aqueous solution system. The adsorption of Pt(IV) and Pd(II) onto G600 reached equilibrium within 24h. The experimental data fit the pseudo-second-order model (correlation coefficient: 0.986–0.995) better than the pseudo-first-order model (correlation coefficient: 0.879–0.973). Moreover, the Weber–Morris plot also was evaluated. The adsorption isotherms of Pt(IV) and Pd(II) onto G600 fit the Freundlich and Langmuir models, respectively. Thus, G600 is useful for the adsorption of Pt(IV) and Pd(II) in aqueous solution.