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

Abstract In this study, the effects of two different ammonium-exchange methods to improve the ammonia (NH 3 ) 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 NH 4 NO 3 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 NH 3 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 NH 3 adsorption properties of the selected parent CLN sample, cation-exchange processes were carried out using 0.5 and 1.0 M NaNO 3 , KNO 3 , Ca(NO 3 ) 2 and Mg(NO 3 ) 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 N 2 adsorption analyses. Cation-exchanged samples with a wide range of NH 3 adsorption capacities (3.61–4.93 mmol g –1 ) were compared with other zeolites from the literature.