Fixed-Bed Catalytic Oxidative Removal of Dissolved Iron by Manganese Oxide-Coated Clinoptilolite: Enhanced Activity in the Presence of Aqueous Mn2+ Cations

Abstract

The kinetics for the fixed-bed catalytic oxidative removal of Fe2+ from aqueous feeds with and without the presence of Mn2+ cations by manganese oxide-coated clinoptilolite zeolite granules has been investigated for the first time. The feed flow rate under study were 40, 60 and 80 cm3 min−1. The initial Fe2+ or Mn2+ concentrations were 50 ppm. The continuous operation system exhibited two peculiarities: (1) In the absence of Mn2+ cations, the catalyst undergoes gradual and continuous deactivation but assumes a finite value of activity at long times (steady-state activity); (2) In the presence of Mn2+ in the liquid phase, the deactivation rate increases substantially while the final activity of the catalyst increases significantly. The gradual deactivation in the absence of Mn2+ is mainly due to the blinding of the active sites by Fe(III) species precipitates. In the presence of Mn2+ cations, the deactivation rate is highly enhanced due to the physical adsorption of these ions on the catalyst exposed surface. The increase in the permanent activity in the presence of Mn2+ cations in the liquid phase has been attributed to the creation of new active sites, mediated by the presence of the precipitated iron (III) species on the composite catalyst surface. The deductions are supported by Raman, XPS and XRD analysis of the catalysts.