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 (CO32–) 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 CO32– and HCO3– anions from the waste solution. The mechanism for the sequestration of CO32– and HCO3– anions from the waste solution using ettringite suggested that the removal of CO32– 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 CO32– 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.