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The kinetic data determined for each model and the correlation coefficient (r2) are shown in Table 2. As can be shown from the results, the two models exhibit a reasonably good agreement with the experimental data, but comparison between the r2 values, indicates that the pseudo-second-order model gives the perfect overall fit. Furthermore, the adsorbed amounts at equilibrium calculated (qe,cal) by this model are also a good fit with the experimental values (qe,exp). The good fit with experimental data for all samples confirm that the velocity control mechanism of adsorption is chemical adsorption. Similar results for chemical adsorption of removal of dye contaminants onto LDHs were found by Zhu et al. (2005).

Table 2

Pseudo-first-order model and pseudo-second-order model parameters for MO adsorption by LDHs

Pseudo-first-order model
Pseudo-second-order model
Adsorbentqexp (mg/g)qe, cal (mg/g)k1 (1/min)r2qe, cal (mg/g)k2 (g/mg·min)r2
Zn-Al-Cl 211.55 204.63 0.0859 0.973 217.36 0.00062 0.998 
Mg-Al-Cl 166.23 155.78 0.0249 0.949 174.89 0.00019 0.985 
Ni-Al-Cl 124.68 115.64 0.0460 0.910 126.57 0.00054 0.972 
Pseudo-first-order model
Pseudo-second-order model
Adsorbentqexp (mg/g)qe, cal (mg/g)k1 (1/min)r2qe, cal (mg/g)k2 (g/mg·min)r2
Zn-Al-Cl 211.55 204.63 0.0859 0.973 217.36 0.00062 0.998 
Mg-Al-Cl 166.23 155.78 0.0249 0.949 174.89 0.00019 0.985 
Ni-Al-Cl 124.68 115.64 0.0460 0.910 126.57 0.00054 0.972 

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