▪ Abstract Manganese(IV) oxides produced through microbial activity, i.e., biogenic Mn oxides or Mn biooxides, are believed to be the most abundant and highly reactive Mn oxide phases in the environment. They mediate redox reactions with organic and inorganic compounds and sequester a variety of metals. The major pathway for bacterial Mn(II) oxidation is enzymatic, and although bacteria that oxidize Mn(II) are phylogenetically diverse, they require a multicopper oxidase-like enzyme to oxidize Mn(II). The oxidation of Mn(II) to Mn(IV) occurs via a soluble or enzyme-complexed Mn(III) intermediate. The primary Mn(IV) biooxide formed is a phyllomanganate most similar to δ-MnO2 or acid birnessite. Metal sequestration by the Mn biooxides occurs predominantly at vacant layer octahedral sites.

Biogenic manganese oxides: Properties and mechanisms of formation

Iron and manganese in lakes

Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1

Heavy metals (Cd, Pb, Zn, Ni, Cu and Cr(III)) removal from water in Malaysia: Post treatment by high quality limestone

X-ray diffraction (XRD) and Mn K-edge extended X-ray absorption Þ ne structure (EXAFS) spectroscopy were combined to elaborate a structural model for phyllomanganates (layer-type Mn oxides) lacking 3D ordering (turbostratic stacking). These techniques were applied to a sample produced by a common soil and freshwater bacterium (Pseudomonas putida), and to two synthetic analogs, δ-MnO2 and acid birnessite, obtained by the reduction of potassium permanganate with MnCl2 and HCl, respectively. To interpret the diffraction and spectroscopic data, we applied an XRD simulation technique utilized previously for well-crystallized birnessite varieties, complementing this approach with single-scattering-path simulations of the Mn K-edge EXAFS spectra. Our structural analyses revealed that all three Mn oxides have an hexagonal layer symmetry with layers comprising edgesharing Mn 4+ O6 octahedra and cation vacancies, but no layer Mn 3+ O6 octahedra. The proportion of cation vacancies in the layers ranged from 6 to 17%, these vacancies being charge-compensated in the interlayer by protons, alkali metals, and Mn atoms, in amounts that vary with the phyllomanganate species and synthesis medium. Both vacancies and interlayer Mn were most abundant in the biogenic oxide. The diffracting crystallites contained three to six randomly stacked layers and have coherent scattering domains of 19–42 A in the c* direction, and of 60–85 A in the a-b plane. Thus, the Mn oxides investigated here are nanoparticles that bear signiÞ cant permanent structural charge resulting from cation layer vacancies and variable surface charge from unsaturated O atoms at layer edges.

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D.W. Thompson

Papers

Oxidation products of Mn(II) in lake waters