Synthesized Ettringite for Sequestration of Inorganic 14C from the Waste Solution

Carbon-14 (¹⁴C), a radionuclide generated in a nuclear power plant’s operation, is a serious environmental threat due to its long half-life (5730 years) and potential mobility in the environment. Herein, we present the sequestration behavior of inorganic ¹⁴C as carbonate (CO₃^2–) and bicarbonate (HCO₃^–) species from a simulated waste solution using synthesized ettringite under various experimental conditions. The ettringite was synthesized via the solution route and characterized by XRD, FT-IR, N₂ adsorption/desorption isotherms, and FE-SEM/EDS analyses. Synthesized ettringite exhibited an efficient inorganic ¹⁴C removal capacity (∼92–94%) as compared to CO₃^2– and HCO₃^– anions from the waste solution. The mechanism for the sequestration of CO₃^2– and HCO₃^– anions from the waste solution using ettringite suggested that the removal of CO₃^2– and HCO₃^– anions was achieved via ligand exchange and framework dissolution–precipitation, respectively. To investigate the ¹⁴C retention capacity onto ettringite, the study also performed desorption experiments in simulated groundwater (SGW) and the obtained results suggested that the desorption % of both anions was significantly lowered (7 and 4.5% for HCO₃^– and CO₃^2– anions, respectively) in SGW. We believe that our results will be highly significant in interpreting the immobilization behavior of dissolved inorganic ¹⁴C as bicarbonate and carbonate anions present in alkaline waste solutions/aqueous environments.