Decontamination of actual radioactive wastewater containing 137Cs 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 Cs-137 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 degrees K). The adsorption experiments showed a decontamination removal efficiency of about 95.66% of Cs-137. A Freundlich adsorption isotherm model was approved for the adsorption of Cs-137, with a coefficient of determination R-2 = 0.998. A pseudo-second-order model fitted well with the adsorption of Cs-137, with R-2 = 0.983. The positive value of Delta H degrees in the thermodynamic results indicated that the adsorption process was endothermic physisorption (Delta H degrees = 15.01 kJ mol(-1)), spontaneous and favorable (Delta G degrees = -7.66 kJ mol(-1) K-1), with a very low degree of disorder (Delta S degrees = 0.076 kJ mol(-1) K-1).

Automated summary

Batch adsorption using Iraqi bentonite as a natural adsorbent showed a high removal efficiency of about 95.66% for Cs-137 decontamination from radioactive wastewater. The Freundlich adsorption isotherm and pseudo-second-order models were found to be suitable for Cs-137 adsorption. Thermodynamic analysis revealed that the adsorption process was endothermic, spontaneous, and favorable.