Large amounts of contaminant metals (such as Mn, Co, Cu, Ni, and Zn) are present in the Fe-rich mining tailings of the Rio Doce estuary (Brazil), after the rupture disaster of the upstream Fundão tailings dam. The Fe oxides from the tailings may undergo reductive dissolution at the redox dynamic estuary and potentially release the associated metals and cause contamination. Aiming to explore the potential mechanisms of metal release in the estuary, we performed a 20-d lab redox oscillation experiment exposing the mining tailings to three different redox conditions that prevail in the estuary (static anoxic, static oxic, and redox oscillation). We collected samples at the beginning and at the end of the experiment for each treatment and performed the sample characterization for Fe and Mn. Our objective is to use µXRF and µXANES to study the adsorption stability and mapping of Mn onto the Fe-rich mining tailings when exposed different redox conditions that naturally occur at the estuary.