3.6 Sorption isotherms
The experimental adsorption equilibrium data were analyzed using Langmuir, Freundlich, Temkin and D-R isotherms. The sorption data was analyzed using linear form of all the isotherm equations Models having high correlation coefficient (R2 ) values are considered best fit to represent the sorption data.
The Freundlich isotherm holds for multilayer non-ideal adsorption on heterogeneous surface and is represented by the following empirical equation: qe = KF Ce 1/n
Where,
KF = adsorption equilibrium constant (mg/g)
1/n= adsorption intensity of dye onto the adsorbent
Ce = equilibrium concentration of dye (mg/L) qe = the amount of dye adsorbed per gram of the adsorbent at equilibrium (mg/g)
The linear form of Freundlich equation[25] is given below: log qe = log KF +1/n log Ce
The constant KF is an approximate indicator of adsorption capacity of adsorbent and n is a function of the intensity of adsorption. Magnitude of n indicates favorability of …show more content…
The constant b is related to the heat of sorption.
The values of constants A and B are derived from the intercept and slope of plot between ln Ce and qe respectively. It can be seen from the results that the temkin isotherm has a low R2 value so the experimental data do not follow this model. Values of A and B derived from the temkin plot are as follows: A= 0.866 L/g, B=0.855 J/ mol. This model is not applicable for present work as the R2 value is low (0.827). [Table 1]
The Dubinin – Radushkevich (D–R) isotherm model was used to estimate porosity, apparent free energy and characteristic of adsorption. The D–R isotherm does not suppose a homogeneous surface and constant sorption potential and it is shown in the following equation [27]: qe= Qm exp (-KƐ2)
The linear form of D-R isotherm is as: ln qe=ln Qm-KƐ2
The experimental adsorption equilibrium data were analyzed using Langmuir, Freundlich, Temkin and D-R isotherms. The sorption data was analyzed using linear form of all the isotherm equations Models having high correlation coefficient (R2 ) values are considered best fit to represent the sorption data.
The Freundlich isotherm holds for multilayer non-ideal adsorption on heterogeneous surface and is represented by the following empirical equation: qe = KF Ce 1/n
Where,
KF = adsorption equilibrium constant (mg/g)
1/n= adsorption intensity of dye onto the adsorbent
Ce = equilibrium concentration of dye (mg/L) qe = the amount of dye adsorbed per gram of the adsorbent at equilibrium (mg/g)
The linear form of Freundlich equation[25] is given below: log qe = log KF +1/n log Ce
The constant KF is an approximate indicator of adsorption capacity of adsorbent and n is a function of the intensity of adsorption. Magnitude of n indicates favorability of …show more content…
The constant b is related to the heat of sorption.
The values of constants A and B are derived from the intercept and slope of plot between ln Ce and qe respectively. It can be seen from the results that the temkin isotherm has a low R2 value so the experimental data do not follow this model. Values of A and B derived from the temkin plot are as follows: A= 0.866 L/g, B=0.855 J/ mol. This model is not applicable for present work as the R2 value is low (0.827). [Table 1]
The Dubinin – Radushkevich (D–R) isotherm model was used to estimate porosity, apparent free energy and characteristic of adsorption. The D–R isotherm does not suppose a homogeneous surface and constant sorption potential and it is shown in the following equation [27]: qe= Qm exp (-KƐ2)
The linear form of D-R isotherm is as: ln qe=ln Qm-KƐ2