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

This study investigated methane (CH) 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 AgNO, 1 M Cu(NO)∙3HO, 1 M Fe(NO)∙9HO, and 1 M HCl solutions at 80 °C for 6 h, respectively. The natural and modified sepiolite samples were characterized by using X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TG-DTG), differential thermal analysis (DTA), and the nitrogen adsorption method. Quantitative XRD analysis showed that the sample consisted primarily of sepiolite clay mineral and dolomite as an impurity in small amounts. It was found that acid and heavy metal treatments caused apparent changes in the structure and microporosity of the sepiolite samples. CH 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 CH adsorption capacities of sepiolite samples increased at both temperatures according to the following sequence: CuS < AgS < HS < S < FeS. CH adsorption values of sepiolite samples varied between 0.084 mmol/g and 0.299 mmol/g. It was observed that the CH adsorption capacities of heavy metal cation-exchange clay samples were related to the surface area.