Highly efficient removal of antimonite (Sb (III)) from aqueous solutions by organoclay and organozeolite: Kinetics and Isotherms

Clays modified by cationic surfactants have been widely used for the removal of organic and inorganic anionic contaminants. However, their suitability for the removal of antimonite from aqueous solutions has not been systematically studied. In this study, hexadecylpyridinium chloride modified montmorillonite (HDPy⁺-M) and hexadecylpyridinium bromide modified zeolite (HDPy⁺-Z) were used to measure Sb(III) uptake from solutions containing 0.5–2.5 mM antimonite. Adsorption isotherms of antimonite were studied using the Langmuir and Freundlich equations. Adsorption kinetics were investigated using pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models. The results of X-ray diffraction showed a large interlayer expansion for HDPy⁺-M, whereas the X-ray patterns of HDPy⁺-Z remained unchanged. Uptake of Sb(III) by both HDPy⁺-M and HDPy⁺-Z could be fitted well to the Langmuir isotherm, while the kinetics of adsorption could be described well using the pseudo-second-order model. Maximum adsorption capacities for Sb(III) uptake by HDPy⁺-M and HDPy⁺-Z were calculated to be 108.7 and 61.34 mg g⁻¹, respectively. The results of the kinetic studies revealed that Sb(III) adsorption to HDPy⁺-Z was found to be quite fast and the reaction reached equilibrium in 8 h, whereas for HDPy⁺-M equilibration was attained within 24 h. The adsorption of antimonite onto both HDPy⁺-M and HDPy⁺-Z was found to be selective in the presence of Cl⁻¹ and SO₄⁻² competitive anions. Considering the high affinity for Sb(III) uptake from solutions containing high concentrations of antimonite, both HDPy⁺-M and HDPy⁺-Z could be used as promising adsorbents for environmental applications.