Surface complexation adsorption of Tl(III) by Fe and Mn (hydr)oxides

Abstract

Thallium(III) (Tl(III)) is mobile in acidic environments and under ligand complexation, posing a potential threat to the environment and human health. The adsorption of Tl(III) on manganese and iron (hydr)oxides will affect its environmental mobility and engineering removal efficiency. However, the adsorption behavior and interfacial reaction mechanism of Tl(III) remain largely unknown. This study is the first to elucidate the surface complexation mechanism of Tl(III) on Fe/Mn (hydr)oxides and to investigate the adsorption behavior of Tl(III) under the influence of typical environmental ligands. Deprotonation of surface hydroxyl groups contributes to the increase in adsorption capacity for Tl(III) (δ-MnO2, 1619.93 mg g−1; α-FeOOH, 48.25 mg g−1; and α-Fe2O3, 58.66 mg g−1 from Langmuir thermodynamic fitting). Surface complexation modeling reveals tridentate complexation of Tl(III) on birnessite and monodentate complexation on iron (hydr)oxides. The anionic ligand strongly inhibits the adsorption of Tl(III) (up to 16.0 %–40.0 %) by complexing with Tl(III) and occupying the adsorption sites. In addition, HA also reduces the adsorption of Tl(III) by 8.2 %–23.2 % by exacerbating the aggregation and surface coating of the adsorbent particles. New insights into the binding mechanism of Tl(III) on Fe/Mn oxides can help to guide the development of efficient Tl(III) removal adsorbents.