Thermodynamics of ammonium exchange by clinoptilolite

An investigation was conducted to study the effect of temperatures from 298 to 328 degrees K on the kinetics of NH4+ exchange by clinoptilolite using a batch technique, and to elucidate the exchange process using thermodynami c and pseudothermodynamic parameters formulated from experimental data. The rate constants for both adsorption and desorption processes, calculated us ing the modified Freundlich model, increased with increasing temperature. C hanges in rate constants with a 10 degrees K rise in temperature (Q(10)) we re slightly greater than 1, suggesting a diffusion-controlled process. Acti vation energies for adsorption (E-a) and desorption (E-d) were 2.32 and 5.6 5 kJ mol(-1)', respectively. The higher E-d value indicated that more energ y was needed to desorb NH4+ than to adsorb it. The standard enthalpy change (Delta H degrees) for NH4+ exchange was negative, which indicated strong b inding of NH4+ on the exchange sites of the zeolite. The change in free ene rgy (Delta G degrees) values for NH4+ exchange ranged from 50.58 to 269.27 J mol(-1) and increased with increasing temperature.