the biosorption of Cd (II) onto dried biomass of Aphanothece sp may be carried out as chemisorption process involving valence force through sharing or exchange of electron between sorbent and sorbate.
3.7. Thermodynamic Parameter
Thermodynamic behavior of Cd (II) biosorption onto dried biomass of Aphanothece sp was described by using three thermodynamic parameter including of free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0). Estimation of thermodynamic parameter is shown in Figure 3.
Figure 3. Plot of ln Kd against 1/T for the estimationof thermodynamic parameter for biosorption of Cd (II) onto dried biomass of Aphanothece sp.
The free energy change (ΔG0) was calculated to be -9.82, -9.15, -8.70 kJ/mol for the biosorption of Cd (II) at 37, 42 and 47 ⁰C, respectively. Negative values indicated thermodynamically feasible and spontaneous nature of biosorption. The decrease in ΔG0 value with increasing temperature show a decrease in feasibility at higher temperature.
The ΔH0 was found to be -46.24 kJ/mol. The negative ΔH0 is indicator of exothermic nature of biosorption and its magnitude can give information on the type of biosorption which can be either physical or chemical. In this study, biosorption proceeded in chemisorption process because falls into 20.9-418.4 kJ/mol. The ΔS0 parameter found to be -141.90 J/mol K for Cd biosorption. The negative ΔS0 value suggests a decrease in the randomness at a solid/solution interface during the biosorption process.
ACKNOWLEDGEMENT
The authors would like to acknowledge the Indonesian Institute of Sciences and Dept. of Chemical Engineering-FTI Institut Teknologi Bandung for the support of this work.
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