Adsorption Properties of Calcined Modified Sepiolite on SO₄ ²⁻ and Cl⁻

Abstract

Three different kinds of sepiolite (Type A, Type B and Sepiolite fiber) were processed by calcination and analyzed by thermogravimetric analysis (TG), X-ray diffraction diffractometer (XRD), scanning electron microscopy (SEM), BET (specific surface area from N2 adsorption isotherms), mercury intrusion porosimetry (MIP), and infrared spectroscopic analysis (IR), respectively. The results show that the adsorption performance of sepiolite can be changed by calcination and environment temperatures, especially for calcination. The adsorption capacity of sepiolite fiber is bigger than that of Type A and B, and adsorption capacity of each sepiolite to sulfate is smaller than that of the chloride ions. Especially, the maximum value for adsorption of the sepiolite fibers, calcined at 600 ℃ and water bath at 60 ℃, to chlorine ion and sulfate are 5.95 and 5.71 mg/g, respectively (mg/g: the ions quantity adsorbed by a unit of sepiolite weight). The minimum adsorption of calcined sepiolite fiber to sulfate ions increased from 5.02 to 5.55 mg/g. While microstructure analysis of sepiolite by TG indicated that its structure was, for temperature not exceeding 700 ℃, was not changed significantly. Sepiolite has a porous structure, especially for sepiolite fiber, which can be observed by SEM. BET indicates that sepiolite fiber has a larger pore volume than others and this can be increased by calcination. IR shows that the adsorption of sepiolite to Cl- and SO4 2- belongs to physical absorption, instead of chemisorption.

Keywords

adsorption / chloridion / sepiolite / sulfate ion / temperature