Interaction mechanism of hausmannite and Mn2+ under oxic conditions: Catalytic oxidation of Mn2+ to low-valence manganese oxides and mineral phase transformation

Hausmannite is a common and widely distributed low-valence manganese oxide in soils and sediments. The transformation of this metastable mineral greatly influences the toxicity and geochemical cycling of trace ele-ments. Mn2+ aq can be adsorbed and oxidized by Mn(III)/Mn(IV) oxides and influences the transformation of these minerals, while little attention has been paid on the interaction between Mn2+aq and hausmannite. Here, the interaction process of Mn2+ aq and hausmannite under oxic conditions and the influence of pH, Mn2+aq concentration and oxygen were systematically investigated. Hausmannite was progressively oxidized to manganite in the single hausmannite system. After the addition of Mn2+aq, adsorbed Mn2+ can be slowly catalytically oxidized to manganite by hausmannite and the transformation rate of hausmannite to manganite decreased under oxic conditions. The oxidation rate of Mn2+aq increased with increasing oxygen partial pressure. The generation rate of manganite was the lowest under neutral pH conditions in the reaction system of Mn2+aq and hausmannite. Both hausmannite dissolution at acidic pH and adsorbed Mn2+ oxidation at alkaline pH facilitated manganite for-mation. These findings improve our understanding of the formation and transformation of low-valence man-ganese oxides in natural environments.

Automated summary

The interaction between Mn2+aq and Hausmannite is influenced by pH, Mn2+aq concentration, and oxygen. Under oxic conditions, the transformation of Hausmannite to Manganite can be catalyzed by adsorbed Mn2+, with the generation rate of Manganite being lowest at neutral pH.