Adsorption behavior of Sb(III) on iron-functionalized attapulgite in aqueous solution

Sb, a toxic metal, exists widely in water and thus poses a serious environmental problem. This study presented the development of a novel and efficient iron-functionalized attapulgite (Fe-ATP) adsorbent, on which the adsorption behavior of antimony (Sb) from aqueous solutions was investigated. A variety of techniques, such as scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier-transform infrared spectroscopy, were used to characterize Fe-ATP. The influence of pH, temperature, and coexisting ions on adsorption was discussed. The results showed that the adsorption process reached equilibrium within 180 min at an initial Sb(III) concentration of 10 mg/L. The pH critically affected adsorption; the removal percentages were 92% and 62% at pH 4 and 13, respectively. The adsorption principles fitted the Freundlich model (R-2 > 0.990) and the pseudo-second-order model (R-2 > 0.999) well, indicating that the process was predominantly controlled by chemical processes. The enthalpy change of 6.5 kJ/mol and negative Gibbs free energy change indicated that adsorption was endothermic and spontaneous. It was also proven that the Fe-ATP was a recyclable adsorbent based on desorption experiments using ethylenediaminetetraacetic acid and NaOH solutions. The findings of the present work highlight the potential applicability of Fe-ATP as an effective sorbent for the selective removal of Sb(III) in water treatment processes.