where q is the metal uptake capacity (mg of metal/g dry weight of
biosorbent) and Ce is the concentration of metal ions in the solution
(mg/L) when equilibrium is reached, qmax is the uptake capacity when
the surface is completely covered with metal ions (maximum uptake
capacity), and b is a constant that represents the affinity between the
biosorbent and the metal ion.
The Freundlich isotherm is an empirical expression that takes into
account the heterogeneity of the surface and multilayer adsorption to
the binding sites located on the surface of the sorbent. The Freundlich
[31] model is expressed as follows