Removal of gases by thermal-acid leached kaolinitic clays: Influence of mineralogical composition

Natural and modified kaolinitic clays were used as retention for gas adsorptions. The kaolinitic clays containing different mineralogical compositions were used. The modifications were carried out by heating the clays at 600 °C and then by acid treatment with 2.5 mol/L sulphuric acid solution at boiling temperature for 180 min. Equilibrium adsorption was measured using a volumetric apparatus, at 25 °C and 0.1 MPa. The gases tested were N2, O2, CO, CO2, CH4, C2H2 and SO2. The samples were characterised by chemical analysis, BET surface area, X-ray diffraction and infrared spectroscopy. The thermal-acid modifications on kaolins improved the capacity of the clays for gas adsorptions. Retention of SO2 (0.914-1.242 mmol/g), C2H2 (0.450-0.721 mmol/g) and CO2 (0.437-0.602 mmol/g) by modified clays were higher than the other gases previously mentioned. The external surface area and amorphous silica developed by modified clays, due mainly to presence of kaolinite in raw clays, improved the capacity for gas retention. Whereas the main cause for gas retention by raw kaolinitic materials was the presence of the illite phase in raw kaolin clays. The thermal-acid kaolins could be potential solids for separations of gases mixtures.