Comparison of the Cd(II) adsorption processes between boehmite (γ-AlOOH) and goethite (α-FeOOH)

Boehmite and goethite were synthesized and characterized to compare their adsorptive properties for Cd(II) from aqueous solutions. The influences of different parameters, such as contact time, initial cadmium concentration, pH and temperature, on the adsorption processes were investigated. It was found that the Cd(II) adsorption on boehmite was higher than that for goethite, according to the adsorption isotherms. Kinetic studies also showed that the relative adsorption rate of boehmite was similar to that of goethite, and the adsorption processes was described by the pseudo-second-order kinetic model. In both cases, equilibrium was reached within 24 h, and the uptake was affected by intraparticle diffusion. Furthermore, the Cd(II) adsorption behaviors on both of the oxy-hydroxide adsorbents were described reasonably well by the Freundlich isotherm model. For both adsorbents, the Cd(II) adsorption was maximized with basic pH values and was negligible with acid pH values when equilibrium was reached. Lastly, the thermodynamic parameters (ΔH0, ΔG0 and ΔS0) showed that Cd(II) adsorption by both materials was endothermic and spontaneous.

Figure optionsDownload as PowerPoint slideHighlights
► Adsorption capacity of boehmite towards Cd2+ is higher than that of goethite.
► Pseudo second order rate kinetics provided good description of the adsorption data.
► The intraparticle diffusion of Cd(II) in boehmite and goethite was observed.
► Cd(II) adsorption on both minerals was adequately described by Freundlich model.
► Cd(II) adsorption on both adsorbents was spontaneous and endothermic.