Dissolution and phase transformation processes of hausmannite in acidic aqueous systems under anoxic conditions

Hausmannite dissolution is initiated and promoted by protons. At pH ≤ 3.0, hausmannite is first disproportionated to layer-structured birnessite (δ-MnO2), which is then transformed to tunnel-structured Mn(IV) oxide through the transfer of electrons from adsorbed Mn(II) to structural Mn(IV). The presence of K+ promotes the transformation from δ-MnO2 to cryptomelane.210