Kinetics and thermodynamics study of copper ions removal by natural clinoptilolite

Abstract

The process of removal of copper ions by means of clinoptilolite type natural zeolite has been studied as a function of the particle size and temperature. Results indicate that increase in temperature and decrease of particle size improves the removal of copper from aqueous solutions. The parabolic diffusion model is well described process in all examined range of time and it shows that the calculated diffusion coefficient increases with temperature. This increase is more visible at higher particle sizes what assume diffusion through zeolite particle as main mass transfer mechanism. The film diffusion model provides calculation of initial sorption rate (<i style="">k</i>´) and dimensionless parameter proportional to the diffusion film thickness (<i style="">x</i>_i), in relation of particle size and temperature. Diffusion from the surface of zeolite particles through the micro and macro pores is well described with homogenous diffusion model, where change of the calculated overall rate constant is observed at »60 min of the process. This indicates the change of mass transfer rate through porous zeolite particle.

The activation energy (<i style="">E</i>_a), activation enthalpy (<img src='/image/spc_char/delta.gif' border=0><i style="">H</i>), activation entropy (<img src='/image/spc_char/delta.gif' border=0><i style="">S</i>) and free energy of activation (<img src='/image/spc_char/delta.gif' border=0><i style="">G</i>) have been calculated based on kinetic data. These thermodynamic parameters characterize process as diffusion dependent, weakly endothermic and nonspontaneous, where structural changes in structure of natural zeolite particle are not observed.