The Freundlich parameters (K F and N ) were calculated using the equation View the MathML source, where q is the sorbed amount per unit weight of sorbent (mg kg−1), Ce is the equilibrium concentration (mg l−1), KF (mg kg−1)/(mg l−1)N is the Freundlich distribution coefficient which represents the affinity of the sorption, and N (dimensionless) is the nonlinearity or site-energy heterogeneity factor.