The
adsorption capacity increased gradually by time, indicating the
successive adsorption of Cu(II) ions on the adsorbent surface. That
indicates the strong bond formed between the adsorbent and metal
ions [30]. The intercepts (C) in Fig. 5a–d are not equal to zero
(Table 3), which indicates that the intraparticle diffusion model is
the controlling model to determine the kinetics of the adsorption
process [2].