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 10meq/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^-9cm²/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 12.3BV for Pb²⁺ and 1.18 for Cu²⁺. Flow rate is also influencing the operating capacity, giving values between 0.433meq/g_{clinoptilolite} 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.