Equilibrium and kinetic ion exchange studies of Pb²⁺, Cr³⁺, Fe³⁺ and Cu²⁺ on natural clinoptilolite

In the present study ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite is examined at 27±1°C and initial concentration of 10 meq/dm3. Equilibrium is favorable for Pb2+, unfavorable for Cu2+ and sigmoid for Cr3+ and Fe3+. Selectivity series deduced from equilibrium isotherms is Pb2+>Cr3+>Fe3+>Cu2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb2+>Cr3+≅Cu2+⩾Fe3+. Cu2+ manifests the higher value of diffusion coefficient in the clinoptilolite particles among the metals studied, equal to 1.40×10−9 cm2/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 Pb2+ and 1.18 for Cu2+. Flow rate is also influencing the operating capacity, giving values between 0.433 meq/gclinoptilolite for Pb2+ and 0.053 for Fe3+. Breakthrough point values confirm the selectivity order deduced from the equilibrium isotherms, while operating capacity values confirm the selectivity order deduced from MEL experiments.