Removal of Radio and Stable Isotopes of Cobalt and Cesium from Contaminated Aqueous Solutions by Isatin-Derived Ligand

This study investigated the effectiveness of a ligand known as (2-Mercapyo-phenylimino)-1,3-dihydro-indol-2-one-based ligand, in removing stable/radioactive cesium and cobalt from contaminated wastewater. Several parameters, such as contact duration, temperature, adsorbent quantity, pH of the medium, and concentration of adsorbate, have been investigated as primary active parameters impacting the adsorption process. Regarding the stable isotopes, the concentrations of Co2+ and Cs+ were measured before and after the treatment processes using the Optical Emissions Spectroscopy with Inductively Coupled Plasma (ICP-OES) technique. Additionally, kinetic and equilibrium isotherm models were applied to understand the equilibrium data. Both Cs+ and Co2+ were ideally eliminated after 120 and 60 min, respectively. The optimal pH for Cs+ was 6.3, while that for Co2+ was 5. The results indicate that the adsorption process is endothermic for Co2+ and exothermic for Cs+. Three thermodynamic parameters (∆G°, ∆H°, and ∆S°) were calculated. The reported R2 values for the Freundlich and Langmuir models showed that the adsorption process for Cs+ and Co2+ always followed these isotherms, regardless of the temperature used. For Cs+, the maximum single-layer capacity (qmax) was 15.10 mg g−1, while for Co2+, it was 62.11 mg g−1. When the aqueous medium was spiked with both radioisotopes individually, the elimination of 60Co and 134Cs achieved maximum values of 99 and 86%, respectively, within 120 min. It can be concluded that the ligand effectively removed cobalt and cesium from wastewater, with higher adsorption for cobalt.