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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):
formula
10
where qe is the amount of metal adsorbed at equilibrium (mg/g), qt is the amount of metal adsorbed at a given time t and k1 is the first-order adsorption rate constant (min–1). The plot of log (qe – qt) against time is a straight line with a slope of k1/2.303 and intercept log qe. Figure 6 shows the plot of the pseudo first-order linear model for zinc removal. The values of R2, K1, and qe deduced from the straight line plot are shown in Table 4. The model correlation of determination (R2) 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 qe 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.
Table 4

Pseudo first and second-order reaction rate constants values for zinc adsorption

 Pseudo first-order model
Pseudo second-order model
Zinc initial concentration (mg/L)qe, exp (mg/g)k1 (min–1)qe, cal (mg/g)R2k2 (g /min mg)qe, cal (mg/g)R2
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)qe, exp (mg/g)k1 (min–1)qe, cal (mg/g)R2k2 (g /min mg)qe, cal (mg/g)R2
100 19.14 0.007 4.42 0.82 0.0523 19.12 0.99 

qe, cal = calculated value from model, qe,exp = experimental value.

Figure 6

Pseudo first-order kinetic plot for the adsorption of metal ion zinc.

Figure 6

Pseudo first-order kinetic plot for the adsorption of metal ion zinc.

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