The experimental data obtained was tested using pseudo first and second-order kinetic models. The two models are used to investigate the adsorption mechanisms and the potential rates regulating the steps involved, such as chemical reaction and mass transport processes. The adsorbents, physical and chemical characteristics play a vital role in determining its adsorption mechanism. The pseudo first-order kinetic model can be expressed in the form of Equation (10) (Taty-Costodes *et al.* 2003):where *q*_{e} is the amount of metal adsorbed at equilibrium (mg/g), *q*_{t} is the amount of metal adsorbed at a given time *t* and *k*_{1} is the first-order adsorption rate constant (min^{–1}). The plot of log (*q*_{e} – q_{t}) against time is a straight line with a slope of *k*_{1}/2.303 and intercept log *q*_{e}. Figure 6 shows the plot of the pseudo first-order linear model for zinc removal. The values of *R*^{2}, K_{1,} and *q*_{e} deduced from the straight line plot are shown in Table 4. The model correlation of determination (*R*^{2}) was found to be 0.82. This shows that the model has a poor correlation value to fit the data best. It can also be seen that the experimental value of *q*_{e} did not go along with the computed value obtained from the plot. Thus, it could be resolved that the first-order kinetic model does not have an adequate value to be projected as an appropriate model. Mishra & Patel (2009) have reported a similar phenomenon on the removal of lead and zinc ions from water by low cost adsorbents.

10

Table 4

. | Pseudo first-order model . | Pseudo second-order model . | |||||
---|---|---|---|---|---|---|---|

Zinc initial concentration (mg/L) . | q_{e}_{, exp} (mg/g)
. | k_{1} (min^{–1})
. | q_{e}_{, cal} (mg/g)
. | R^{2}
. | k^{2} (g /min mg)
. | q_{e, cal} (mg/g)
. | R^{2}
. |

100 | 19.14 | 0.007 | 4.42 | 0.82 | 0.0523 | 19.12 | 0.99 |

. | Pseudo first-order model . | Pseudo second-order model . | |||||
---|---|---|---|---|---|---|---|

Zinc initial concentration (mg/L) . | q_{e}_{, exp} (mg/g)
. | k_{1} (min^{–1})
. | q_{e}_{, cal} (mg/g)
. | R^{2}
. | k^{2} (g /min mg)
. | q_{e, cal} (mg/g)
. | R^{2}
. |

100 | 19.14 | 0.007 | 4.42 | 0.82 | 0.0523 | 19.12 | 0.99 |

*q _{e, cal}* = calculated value from model,

Figure 6

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