The values of the mean free energy E (kJ mol−1) calculated with Dubinin–Radushkevich isotherm confirm that the lead (II) adsorption process onto allspice residue is controlled by chemisorption. According to some authors [20] if E < 8 kJ mol−1, the adsorption process is of physical nature, but if 8 < E < 16 kJ mol−1 then it is a chemical phenomenon.