NATURAL ZEOLITES AND SEPIOLITE AS AMMONIUM AND AMMONIA ADSORBENT MATERIALS

Zeolite clinoptilolite is a natural mineral with ion-exchange and gas-adsorption properties. Ammonium- and ammonia-adsorption processes were studied in the zeolite clinoptilolite and zeolite-like sepiolite minerals. Maximum adsorption capacities of both ammonium and ammonia were determined by fitting the experimental results of the adsorption isotherm to Langmuir and first-order models. Ammonium-adsorption capacities of the zeolites were from 8.149 to 15-169 mg N g-1; up to 10.3 times higher than that of sepiolite. Ammonium-adsorption capacity increased with the surface charge density of the material, due to the readily available exchange sites in the surface. Ammonia-adsorption capacities of the zeolites were between 6.255 and 14.155 mg N g-1. Because of its large surface area, sepiolite had a capacity of ammonia adsorption three times higher than that of the ammonium ion. The complexity of the ammonia-adsorption process meant that no individual characteristics of the materials influenced directly the adsorption capacity. However, ammonia adsorption was enhanced on the ammonium adsorption in zeolites with relatively low surface charge density.