Pb²⁺ Adsorption of Spray-Dried Na-FAU Zeolite

Abstract

Pb²⁺ adsorption equilibrium and kinetic of spray-dried zeolites were investigated. Spray-drying of synthesized Na-FAU zeolite (Si/Al ratio=3.2, primary particle size=0.34 µm) obtained spherical agglomerate with hollow structure, preserving the crystal and micropore structures. The geometric mean diameters and tapped densities of the spray-dried zeolite varied with heating temperature and zeolite concentration, ranging from 0.93–1.64 µm and 0.28–0.32 g/cm³, respectively. Spray-dried zeolite showed saturated Pb²⁺ adsorption amount of 385 mg-Pb²⁺/g, consistent to the powder dried in a thermostatic oven at 80°C (Pow-Y). Spray-dried zeolite reached Pb²⁺ adsorption equilibrium in about 10 s, significantly faster than Pow-Y. The Pb²⁺ adsorption kinetics of the samples were analyzed by the film-pore-surface diffusion model. The Biot number, which represents the ratio of external mass transfer to intraparticle diffusion, was higher than 200, indicating that intraparticle diffusion is the rate-limiting step for Pb²⁺ adsorption in spray-dried zeolite. Furthermore, the time for adsorptive removal of Pb²⁺ below the effluent standard (0.01 mg/L) for spray-dried zeolite was estimated to be more than 1000 times shorter than that for Pow-Y, using the film-pore-surface diffusion model.