Comparison of bismuth ferrites for chloride removal: Removal efficiency, stability, and structure

The chloride (Cl − ) ions in wastewater are difficult to remove, since there is a lack of effective and recyclable chloride removal agents. In this study, the bismuth ferrites (BFO) are first explored as chloride removal agents, and their oxidation or precipitation effects on the Cl − removal are studied. In the BFO samples, the crystal phases of BiFeO 3 and Bi 2 FeO 4 have very limited contributions to the Cl − removal, while the enhanced removal ability is exhibited with the increase of Bi 25 FeO 40 . When the mass percentage of Bi 25 FeO 40 reaches 70%, high Cl − removal efficiencies of 80–90% are achieved, which even exceeds 95% for pure Bi 25 FeO 40 . The morphology and structure characterizations reveal that the excellent Cl − removal performance of Bi 25 FeO 40 is determined by its unstable chemical structure due to the sharing of Bi 5+ and Fe 3+ ions in the tetrahedral positions. The density of states and electron localization function of Bi 25 FeO 40 demonstrate that its Fe and O bonding is weaker than those of BiFeO 3 and Bi 2 FeO 4 , resulting in the easier breaking of the Fe 3+ /Bi 5+ -O bonds to release Bi 5+ ions, which have oxidation ability for the formation of OH and Cl radicals to enhance the Cl − removal efficiency.