Dye adsorption on a heterogeneous surface is assumed not to be restricted to a monomolecular layer, leading to the proposed Freundlich model (Balarak *et al.* 2015). The Freundlich equation was used to examine equilibrium data for MR adsorption onto AC from orange peels. The straight line with an intercept of ln *K*_{F} and a slope of 1/*n* can be seen in the plot of ln *q*_{e} vs. ln *C*_{e} which is shown in Figure 11. The Freundlich model correlation coefficients (*R*^{2}) suggest that experimental data fitted to the model, and *n* > 1 indicates that dye adsorption onto orange peel AC is a favorable adsorption process. When compared with the Langmuir isotherm models, the *R*^{2} value suggests that the Freundlich isotherm is less relevant. Table 3 shows the Freundlich isotherm constants.

Table 3

Temperature (°C) . | Constants . | Magnitude . |
---|---|---|

60 °C | K_{F} (mg g^{−1}) (mg^{3}/g)^{1/n} | 8.07 |

n | 1.96 | |

R^{2} | 0.966 |

Temperature (°C) . | Constants . | Magnitude . |
---|---|---|

60 °C | K_{F} (mg g^{−1}) (mg^{3}/g)^{1/n} | 8.07 |

n | 1.96 | |

R^{2} | 0.966 |

Figure 11

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