Birnessite Dissolution at the Mineral–Ligand Interface: A Deferoxamine Pathway

Siderophores are natural chelators produced by microorganisms to increase ferric iron availability. Although interactions between deferoxamine (DEFO) and manganese (hydr)oxides have been widely studied, the mechanism of Mn extraction by DEFO from manganese (hydr)oxides remains unclear. This study investigates the specific interaction between DEFO and birnessite, a layered manganese(IV) oxide. The formation of radical species during the DEFO-birnessite interaction was monitored by some methods, including X-ray diffraction (XRD), ultraviolet-visible absorption spectroscopy (UV-Vis), electron paramagnetic resonance (EPR) spectroscopy, energy-dispersive X-ray (EDX)-mapping analysis, and field-emission scanning electron microscopy (FE-SEM). The transient Mn(III) formed appears to coordinate with DEFO, and is subsequently reduced further to Mn(II), resulting in the formation of a Mn(II)-DEFO complex. These results indicate that DEFO is oxidized while birnessite's manganese is reduced (Mn(IV) → Mn(III) → Mn(II)), with radical intermediates observed.