From: Fe(II) reduction of pyrolusite (β-MnO2) and secondary mineral evolution
Mn-oxide substrate | Fe-oxide formed | Conditions | Notes | References |
---|---|---|---|---|
Birnessite [δ-MnO2] | FeOOH | pH 3–6 | Fe(III) stays in solution for pH < 4 and XRD inconclusive | [18] |
Birnessite [δ-MnO2] | Lepidocrocite and trace goethite | pH 4–6 | Higher pH produces more goethite, noncrystalline Fe-oxide | [32] |
Hexagonal birnessite | Lepidocrocite and goethite | pH 4–7 | Less goethite under anoxic conditions compared to oxic | [48] |
Cryptomelane [KMn8O16] | Akaganeite-FeOOH | pH 3–6 | – | [20] |
Hausmannite [Mn3O4] | Magnetite Fe3O4 | pH 3–6 | – | [20] |
MnO2 | Fe(OH)3 | – | – | [15] |
MnO2 | Fe(OH)3; 6-line ferrihydrite | Column pH 2.5–6 | Natural Mn-oxide coated sand | [19] |
Pyrolusite [β-MnO2] | Fe-oxyhydroxide, lepidocrocite | pH 3–6 | – | [20] |
Pyrolusite coated silica sand | 2-line ferrihydrite and jacobsite (MnFe2O4) | pH 3 | Fe(III) precipitates inhibit reductive dissolution of pyrolusite by Fe(II) | [16] |
Pyrolusite coated quartz | Schwertmannite or sulfate-substituted ferrihydrite | pH 3 | – | [17] |
Poorly crystalline MnO2 (similar to birnessite) and freshwater sediment | Amorphic Fe(III) oxide | pH 7 | – | [49] |
Vernadite [δ-MnO2] | Fe2O3 | pH 7.4 | Fe phase proposed in equation but not characterized | [50] |