Surface Complexation Adsorption of Tl(Iii) on Fe and Mn (Hydr)Oxides: Effects of Anions and Organic Ligands

Thallium(III) (Tl(III)) is mobile in acidic environments and under ligand complexation, posing a potential threat to the environment and to human health. Scavenging of Tl(III) by environmental manganese and iron (hydr)oxides will severely affect its reactivity, mobility and bioavailability. However, the adsorption behavior and interfacial reaction mechanism of Tl(III) remain largely unknown. This study is the first to reveal the surface complexation mechanism of Tl(III) on Fe/Mn minerals and to investigate the adsorption behavior of Tl(III) under the influence of typical environmental ligands. The degree of of surface hydroxyl deprotonation significantly affected the adsorption capacity of Tl(III) (δ-MnO2, 1619.93 mg g-1; α-FeOOH, 93.25 mg g-1; and α-Fe2O3, 176.66 mg g-1 from Langmuir thermodynamic fitting). The surface complexation model was applied to reveal tridentate complexation of Tl(III) on birnessite and monodentate complexation on iron (hydr)oxides. The anion ligands significantly inhibited the formation of Tl(III) complexes on mineral surfaces by complexing Tl(III) and occupying mineral adsorption sites. In addition, HA may attenuate the binding of Tl(III) to mineral adsorption sites by partially reducing Tl(III) and coating the mineral surface. New insights into the binding modes and mechanisms of Tl(III) on Fe/Mn minerals contribute to the understanding of environmental Tl(III) transport and transformation.