slope and intercept, respectively. The values of standard Gibbs
free energy change (DG8), standard enthalpy change (DH8) and
standard entropy change (DS8) are presented in Table 5. The
overall free energy changes during the adsorption process at 25,
35 and 45 8C are negative, corresponding to a spontaneous and
thermodynamically favorable process of adsorption of Cu(II) and
Co(II) ions by the synthesized biosorbents. The positive values of
the enthalpy changes indicate that the adsorption is endothermic
in nature. Endothermic adsorption of Cu(II) and Co(II) ions
biosorbents has been reported [34]. The negative and infinite