Adsorption of Sulfate Ions from Aqueous Solution by Surfactant-Modified Palygorskite

The objectives of this work are to study palygorskite modified by a surfactant, octodecyltrimethylammonium chloride (OTMAC), and to study for the potential use of the surfactant-modified palygorskite (SMP) as an adsorbent for the adsorption of sulfate ions from aqueous solutions. The surface characters of SMP were undertaken by scanning electron microscopy (SEM), FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), and N(2) adsorption. The FTIR spectra and XPS showed that the surfactant (OTMAC) had effectively grafted on palygorskite. A batch technique was carried out to evaluate parameters affecting adsorption including pH, the amount of SMP, treatment time, and initial SO(4)(2-) concentration. The adsorption isotherms of SMP for sulfate ions were described by Langmuir, Freundlich, and Dubinin-Radushkevich equations, and the Freundlich model was best to express the adsorption process. The thermodynamic data indicated that the adsorption was an endothermic and spontaneous process. Results of kinetic experiments showed that the adsorption was best described by the pseudosecond-order kinetics model. Above all, the adsorption of sulfate ions extended the application of palygorskite to the removal of anions and wastewater purification.