Pyrogenic carbon for decontamination of low-level radioactive effluents: Simultaneous separation of 137Cs and 60Co

Abstract Radiocesium (137Cs) and radiocobalt (60Co) represent main dose-significant radionuclides in low-level radioactive liquid effluents released from commercial nuclear power plants (NPPs). Although pyrogenic carbon-based adsorbents (biochars, BC) have been studied for toxic metal removal, the reports of their use in the adsorption of radionuclides are rare. This article focuses on the competitive removal of Cs+ and Co2+ ions from radioactive solutions to waste biomass derived biochar and the multi-component isotherms. BC exhibited a good affinity to both Cs and Co, and in single-component systems the maximal adsorption capacity Qmaxexp reached 97.4 ± 5.0 (Cs+) and 74.5 ± 0.4 μmol g−1 (Co2+). 3D adsorption surfaces obtained by Sheindorf-Rebuhn-Steintuch (SRS) and extended Freundlich models indicate that the sorption of Cs+ ions from the Cs–Co binary system is significantly affected by Co2+ ions and during the adsorption competitive and interaction effects between Cs+ and Co2+ ions occur. Moreover, mono- and divalent cations present in the solution acted as competing ions, decreasing the Kd values. SEM-EDX maps, FTIR and XPS spectra confirmed that both biochar mineral and carbon fraction participated in Cs and Co immobilization. Beside interactions of Cs+ and Co2+ ions with O-containing moieties on the biochar surface (chemisorption), mineral components and porosity of BC (physisorption) were involved in both Cs and Co removal. Finally, the adsorption loading and fast kinetics for both Cs and Co indicate suitability of biochar to decontaminate low-level radioactive effluents contaminated by 137Cs and 60Co.