Structural study of Fe(II) adsorption on hematite ( 1 1 ¯ 02 )

The structure of α - Fe 2 O 3 ( 1 1 ¯ 02 ) reacted with Fe(II) under anoxic conditions was studied using crystal truncation rod (CTR) diffraction. The CTR results show the crystalline termination of α - Fe 2 O 3 ( 1 1 ¯ 02 ) is modified due to adsorption of Fe(II) at crystallographic lattice sites. In addition, the binding sites for adsorbed Fe are similar for all studied conditions: reaction for 2 h at pH 5.0, for 34 d at pH 5.0, and for 5.5 h at pH 7.0. The occupancy of adsorbed Fe increases with both reaction time and pH, which is consistent with typical cation adsorption behavior on iron (hydr)oxide surfaces. The metal–oxygen bond lengths of the (ordered) surface Fe atoms are characteristic of Fe(III), which provides indirect evidence for oxidation of adsorbed Fe(II) and is consistent with recent studies indicating that Fe(III)-hydroxides are effective oxidants for dissolved ferrous iron. Grazing-incidence X-ray diffraction measurements indicate that no crystalline surface reaction products formed during the course of Fe(II) reaction. Overall, the structural characterization of the Fe(II) adsorption reaction results in an enhanced understanding of how reduced iron affects the structure, stability and reactivity of hematite.