Improvement of the Stability of IO₃^–-, SeO₃^2–-, and SeO₄^2–-Coprecipitated Barite after Treatment with Phosphate

Abstract

Coprecipitation of radionuclides with barite has been studied to remove radionuclides from radioactive liquid waste because of its excellent removal efficiency; however, little information exists concerning the stability of the ions coprecipitated with barite. This study systematically investigated the stability of iodate, selenite, and selenate coprecipitated with barite via leaching tests. These oxyanions were gradually leached from the oxyanionbearing barite into ultrapure water over time. Leaching of the oxyanions significantly increased in leaching solutions containing NaCl (pH 5.3), NaNO 3 (pH 5.9), and Na 2 SO 4 (pH 5.7). Conversely, leaching of the oxyanions was suppressed in KH 2 PO 4 solution (pH 8.5), indicating that phosphate stabilized the oxyanion-bearing barite. The effect of phosphate treatment on oxyanion-bearing barite was further investigated. The results showed that the barite surface was modified with phosphate, and a thin surface layer of a barium phosphate-like structure was formed. The amount of oxyanions leached from the phosphate-treated samples into leaching solutions containing NaCl or NaNO 3 was much lower than the amounts leached from the untreated barite samples into ultrapure water. The barite coprecipitation combined with subsequent phosphate treatment may be a promising method to efficiently remove iodate, selenite, and selenate from wastewater and stabilize them as barite coprecipitates.

Thermodynamic insights into selenium oxyanion removal from synthetic flue gas desulfurization wastewater with temperature-swing solvent extraction

“…For instance, nano-Al 2 O 3 embedded in chitosan beads were reported to be able to combine photooxidation with adsorption to synergistically remove selenate and selenite; however, their performances were moderately thwarted with the presence of competing sulfate ions (Pincus et al, 2019). Co-precipitation of selenium oxyanions with barite followed by a phosphate post-treatment step to minimize selenium leakage in different aqueous environments was also reported (Tokunaga et al, 2023). Other common practices for the concurrent removal of selenate and selenite involve the use of nanosized zero-valent iron (nZVI).…”