Thermodynamic parameters of TI+, Ra2+, Bi3+ and Ac3+ adsorption onto polyhydroxyethylmethacrylate-hydroxyapatite composite
In this research, a new composite, poly (hydroxyethylmethacrylate-hydroxyapatite) [P(HEMA-Hap)], was synthesized and its adsorptive features for natural radionuclides (TI+, Ra2+, Bi3+ and Ac3+ in a leaching solution) were investigated at differing initial pH, concentration and temperature ranges. The natural radionuclides were counted by gamma spectrometer using a type NAI (Tl) detector. The adsorption data obtained were well represented by Langmuir and Freundlich type isotherms. The magnitude of determined monolayer adsorption capacities (X-L) for the adsorbed radionuclides were TI+ = Ac3+ > Ra2+ = Bi3+. These results demonstrated that P(HEMA-Hap) had high affinity to the natural radionuclide. The thermodynamic parameters indicated that the adsorption mechanisms were spontaneous (Delta G < 0) in terms of adsorption free enthalpy, and changes in the enthalpy and entropy values showed that the overall adsorption process was endothermic (Delta H > 0), thus increasing entropy (Delta S > 0).