Equilibrium and kinetic ion exchange studies of Pb 2+, Cr 3+, Fe 3+ and Cu 2+ on natural clinoptilolite

Abstract

In the present study ion exchange of Pb 2+, Cu 2+, Fe 3+ and Cr 3+ on natural clinoptilolite is examined at 27±1°C and initial concentration of 10 meq/dm 3. Equilibrium is favorable for Pb 2+, unfavorable for Cu 2+ and sigmoid for Cr 3+ and Fe 3+. Selectivity series deduced from equilibrium isotherms is Pb 2+>Cr 3+>Fe 3+>Cu 2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb 2+>Cr 3+≅Cu 2+⩾Fe 3+. Cu 2+ manifests the higher value of diffusion coefficient in the clinoptilolite particles among the metals studied, equal to 1.40×10 −9 cm 2/s. According to the fixed bed experiments the upflow rate (5–15 Bed Volumes (BV)) is influencing the breakthrough point for all metals studied. The breakthrough point varies between 12.3 BV for Pb 2+ and 1.18 for Cu 2+. Flow rate is also influencing the operating capacity, giving values between 0.433 meq/g clinoptilolite for Pb 2+ and 0.053 for Fe 3+. Breakthrough point values confirm the selectivity order deduced from the equilibrium isotherms, while operating capacity values confirm the selectivity order deduced from MEL experiments.