Decontamination of actual radioactive wastewater containing (137)Cs using bentonite as a natural adsorbent: equilibrium, kinetics, and thermodynamic studies

Batch adsorption treatment using Iraqi bentonite as a natural adsorbent was adopted in this study to decontaminate actual (137)Cs radioactive wastewater from the Al-Tuwaitha Nuclear Research Center, located south of Baghdad. The bentonite characterization was applied before and after treatment, using chemical compositions analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) surface area analysis and Fourier-transform infrared spectroscopy (FT-IR). The batch adsorption mode was applied with the initial radioactivity concentration (1440.5 Bq/L), solid/liquid ratio (1 g/L), pH (6–8), contact time (1.5 h), and temperature (298°K). The adsorption experiments showed a decontamination removal efficiency of about 95.66% of (137)Cs. A Freundlich adsorption isotherm model was approved for the adsorption of (137)Cs, with a coefficient of determination R(2) = 0.998. A pseudo-second-order model fitted well with the adsorption of (137)Cs, with R(2) = 0.983. The positive value of ΔH° in the thermodynamic results indicated that the adsorption process was endothermic physisorption (ΔH° = 15.01 kJ mol(−1)), spontaneous and favorable (ΔG° = −7.66 kJ mol(−1) K(−1)), with a very low degree of disorder (ΔS° = 0.076 kJ mol(−1) K(−1)).