ADSORPTION OF H2S AND SO2 ON BIGADIC CLINOPTILOLITE

H2S and SO2 adsorption isotherms of Bigadic clinoptilolite and its Na-, K-, Ca-, and H-enriched forms were determined in the 0 to 100 kPa range at 25 degrees C by using a constant volume adsorption system. Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Dubinin-Astakhov (D-A) models were applied to the isotherm data. Higher adsorption capacities and a larger increase in the amount adsorbed at higher pressures were observed for SO2, in agreement with its higher permanent dipole moment, resulting in stronger ion-dipole and dipole-dipole interactions for this molecule. The Ca-form exhibited a molecular sieving behavior for both gases, originating from the channel blockage caused by the cation locations in the sample. The highest capacities for both gases were obtained with the sample in its H-form, followed by the Na- and K-forms for SO2, parallel to the decrease in the electronegativity and ionic potential and the increase in the polarizability of the cation. In the case of H2S, the H-form was followed by the K-form, but the Na form yielded very low adsorption capacities. Initial dissociative adsorption of H2S on certain Na sites to yield SH and OH species is thought to contribute to a more effective blocking of the channels, which were already partially blocked in this sample. Of the isotherm models tested, the D-A model explained the variations in the data better than either the Freundlich or D-R models. For the cation-gas combinations with a lower extent of channel blockage though, the Langmuir model was somewhat more representative. Lower E and n values were obtained from the D-A model for H2S on the Na-form, which may be related to the lower extent of micropore adsorption and to the presence of blocked, almost dead-end shorter channel segments in the sample. Pore volumes close to the theoretical value were estimated from the D-A parameters for SO2 adsorption.