The kinetics experimental result is shown in Fig. 2. It was found
that 90% of the uptake of tetracycline by the zeolite beta quickly
occurred in 0.25 h, followed by a relative slow process. The adsorption
equilibrium can be established within 3 h. Simulation of tetracycline
sorption kinetics on zeolite beta was conducted by the
intraparticle diffusion model with an assumption of a ‘‘two-step
mass transport mechanism’’. Constant physical properties were assumed.
The mathematical equation and its corresponding initial
and boundary conditions are given as follows [16]: