Removal of Cu(II) from aqueous solutions by using fluidized zeolite A beads: Hydrodynamic and sorption studies

Abstract

This study investigated potentials of fluidized bed systems with zeolite A beads for removal of heavy metal ions from aqueous solutions. Two commercial zeolite bead fractions (0.7 and 2.2 mm in diameter) were used, while Cu(II) served as a model ion. Fluidized bed systems were characterized first regarding the hydrodynamic properties so that the operating regime was determined between the minimum fluidization velocity and the terminal velocity, corresponding to 0.2 and 5.6 cm s(-1), respectively, for smaller beads, and 2.0 and 13.2 cm s(-1), respectively, for larger beads. Cu(II) sorption kinetics was studied next in the fluidized system with recirculation and at the initial Cu(II) concentration of 300 mg dm(-3) at selected superficial velocities of 2.6 and 3.0 cm s(-1), for small and large beads, respectively. In parallel, Cu(II) sorption kinetics was studied in shaken flasks. In both systems and for both zeolite A bead fractions, intra-particle diffusion was shown to be the rate limiting step. Calculated Cu(II) cliffusivities were in the range of (2-15) x 10(-13) m(-2) s(-1) with slightly higher values determined in fluidized bed systems and for larger beads. These slight variations were explained by minor differences in the texture of small and large beads. Still, diffusion through the zeolite lattice was indicated as the slowest step in the process. The maximal sorption capacity of zeolite A beads for Cu(II) at 20 degrees C was predicted as 23.3 mg g(-1) based on the Langmuir model applied to the sorption isotherm. Results from the present study have shown potentials for the use of zeolite A beads in fluidized bed systems for removal of heavy metals from industrial wastewaters.