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Lagergren’s first-order kinetic model

The pseudo-first-order kinetic model of Lagergren is more suitable for lower concentration of solute and its linear form is: log〖(Q_e-Q_t )=log〖Q_e- k_1/2.303 t〗 〗 .................................7

Where, Qt (mg g-1) is the amount of adsorbate adsorbed at time t (min); Qe (mg g-1) is the adsorption capacity in the equilibrium; k1 (min-1) is the rate constant of pseudo-first-order

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The values of k2 for removal of iron by Tribulus Terrestris adsorbents was calculated from the slopes of the respective linear plots of t/Qt vs. t (Figure.10).The correlation coefficients, R2 was 0.994 for Tribulus Terrestris respectively suggest a strong relationship between the parameters and also explain that the process follows pseudo second order kinetics (Table 6 ).

Elovich kinetic model

Elovich model suggests that the chemisorptions, i.e. a chemical reaction, is probably the

Mechanism that controls the rate of adsorption. This model can be applied with success in liquid solution and the linear form of the Elovich equation is: Q_t= 1/β lnαβ+ 1/β lnt ..................................8

Where, α (mg g-1) is the initial sorption rate and β (g mg-1) is the desorption constant. The values of α and β can be calculated from the slope and intercept of the plot of Qt versus ln t