An experimental study on the effect of the acid and heavy metal treatments on the adsorption of CH₄ by sepiolite

Abstract

This study investigated methane (CH₄) adsorption by natural sepiolite—obtained from Eskisehir in Turkey—and its Ag-, Cu-,Fe-, and H-exchanged forms by using a volumetric gas adsorption method. Sepiolite was modified with 1 M AgNO₃, 1 MCu(NO₃)₂∙3H₂O, 1 M Fe(NO₃)₃∙9H₂O, and 1 M HCl solutions at 80 °C for 6 h, respectively. The natural and modified sepiolitesamples were characterized by using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transforminfrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), differential thermal analysis (DTA), and the nitrogenadsorption method. Quantitative XRD analysis showed that the sample consisted primarily of sepiolite clay mineral and dolomiteas an impurity in small amounts. It was found that acid and heavy metal treatments caused apparent changes in the structure andmicroporosity of the sepiolite samples. CH₄ adsorption isotherms of clay samples were examined at temperatures of 0 °C and 25 °C and pressures up to 100 kPa. It was determined that the CH₄ adsorption capacities of sepiolite samples increased at bothtemperatures according to the following sequence: CuS < AgS < HS < S < FeS. CH₄ adsorption values of sepiolite samples variedbetween 0.084 mmol/g and 0.299 mmol/g. It was observed that the CH₄ adsorption capacities of heavy metal cation-exchangeclay samples were related to the surface area.