Natural and pretreated Gördes clinoptilolites for ammonia removal: effect of exchangeable cations (Na+, K+, Ca2+ and Mg2+)

Abstract

Abstract In this study, the effects of two different ammonium-exchange methods to improve the ammonia (NH3) gas adsorption of raw clinoptilolite (CLN) from Gördes (Türkiye) was investigated. The first method involved direct modification of CLN by 0.5 or 1.0 M NH4NO3 solutions at 80°C for 4 and 8 h followed by calcination. In the second method, CLN was converted to the Na+ form prior to modification with ammonium nitrate and calcination under the same conditions. Both methods yielded H+ forms of CLN through the removal of exchangeable cations without damaging the crystal structure. Ammonia adsorption isotherms were determined at 298 K for a total of eight different H+ forms synthetized using both methods. The Na-1.0-8h CLN sample with the highest NH3 adsorption capacity obtained using the second method was selected as the parent CLN. In addition, to determine the effects of doping different cations into the structure on the NH3 adsorption properties of the selected parent CLN sample, cation-exchange processes were carried out using 0.5 and 1.0 M NaNO3, KNO3, Ca(NO3)2 and Mg(NO3)2 solutions at 80°C for 4 h. The raw and modified CLNs were characterized using X-ray diffraction, X-ray fluorescence, scanning electron microscopy and N2 adsorption analyses. Cation-exchanged samples with a wide range of NH3 adsorption capacities (3.61–4.93 mmol g–1) were compared with other zeolites from the literature.