N2 and O2 adsorption properties of an Iranian clinoptilolite-rich tuff in the original and pre-exchanged forms

The adsorption characteristics of an Iranian clinoptilolite-rich tuff from the Semnan region, both in the unmodified and K+, Na+, Ca2+ and Mg2+ exchanged forms has been investigated. The effect of zeolite agglomerate particle size (d < 45 mum, and d = 4 mm) on the adsorption isotherms has been studied. Large ion-exchanged particles exhibit significant less saturation adsorption because of less nanopore connectivity due to minimal residues of unwashed salts. Using the Dubinin-Astakhov model, the optimum values of the structural parameter, characteristic energy, saturation capacity and pore volume have been evaluated. K-cp possesses the largest structural parameter (n = 2.3 for coarse and n = 2.5 for the fine powder). Also, this form has the highest selectivity (amount N-2 adsorbed/amount O-2 adsorbed), i.e., 1.61 and 1.98 for the fine and coarse powders, respectively. The confinement effect is significant in O-2 adsorption for the ion-exchanged forms, resulting in considerable smaller calculated pore volumes. The K+ exchanged Iranian clinoptilolite could be a potential candidate for O-2/N-2 separation while the Ca form is the least appropriate due to eventual blocking of the perpendicular 8 and 10 member-ring channels. (C) 2004 Elsevier B.V. All rights reserved.