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 (R²) 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 R² value suggests that the Freundlich isotherm is less relevant. Table 3 shows the Freundlich isotherm constants.