Removal of manganese in batch and fluidized bed systems using beads of zeolite a as adsorbent

Abstract

In this study the uptake capacity of Mn(II) ions by zeolite A beads was investigated for different initial Mn concentration (100–400 mg Mn dm−3) in batch mode at 25–55 °C. The obtained adsorption capacity varying from 30 to 50 mg Mn g−1 demonstrated a high affinity of zeolite A towards Mn(II) present in solutions. Kinetic studies indicated the intra-particle diffusion as the rate limiting step up to 45 °C with apparent diffusivities in the range (1.2–2.0) × 10−13 m2 s−1 and the activation energy of 21.9 kJ mol−1, which implies strong interactions between the zeolite A and Mn ions. At 55 °C ion-exchange became the rate limiting step. The adsorption isotherms were studied at 25 °C showing that the Mn adsorption is the best described by the Langmuir model suggesting a homogenous zeolite surface. XPS analysis of the Mn-loaded beads showed that there is no surface accumulation of Mn but an almost uniform Mn distribution inside zeolite A, whereas XANES and EXAFS suggested that the adsorption of Mn(II) was followed by the Mn(II) oxidation and oxide formation. Regeneration of the spent zeolite was examined in 8 adsorption/desorption cycles by a chelating Na2EDTA in a fluidized column. It has been found that zeolite A beads could be reused for at least 4 cycles with satisfactory Mn(II) adsorption efficiencies of about 70%.