3.4. Adsorption kinetics
The equilibrium time for adsorption of CIP and NOR on prepared carbon has been determined as 90 and 60 min, respectively. The kinetics data within this range of contact time for each compound are fitted with pseudo-first order, pseudo-second order and intraparticle diffusion models, Eqs. (8)–(10). The results are summarized in Table 3 showing the low R2 values of the pseudo-first order equation for both CIP and NOR. Also, for this model, there is a large difference between the experimental and calculated adsorption capacity for both adsorbates represented by Dq (%), indicating a poor pseudo-first order fit to the experimental data. The linear plot of t/qt versus t (Fig. 5a) for pseudo-second order equation is of high R2 values, as shown in Table 4. The better representation of adsorption kinetics was by the pseudo-second order kinetic model and the calculated qe values agree well with the experimental qe values for both FQs antibiotics (Table 3). This suggests that the adsorption of CIP and NOR on prepared carbon follows second-order kinetics. Several authors showed the successful application of pseudo-second order model for repre- sentation of experimental kinetics data of both CIP and NOR adsorption on agricultural wastes-based carbons [8,10]. From Table 3, the values of rate constant K2 for CIP and NOR decrease with increasing initial concentration.