Real-Time Manganese Phase Dynamics during Biological and Abiotic Manganese Oxide Reduction

Abstract

Manganese oxides are often highly reactive and easily reduced, both abiotically, by a variety of inorganic chemical species, and biologically during anaerobic respiration by microbes. To evaluate the reaction mechanisms of these different reduction routes and their potential lasting products, we measured the sequence progression of microbial manganese(IV) oxide reduction mediated by chemical species (sulfide and ferrous iron) and the common metal-reducing microbe Shewanella oneidensis MR-1 under several endmember conditions, using synchrotron X-ray spectroscopic measurements complemented by X-ray diffraction and Raman spectroscopy on precipitates collected throughout the reaction. Crystalline or potentially long-lived phases produced in these experiments included manganese(II)-phosphate, manganese(II)-carbonate, and manganese(III)-oxyhydroxides. Major controls on the formation of these discrete phases were alkalinity production and solution conditions such as inorganic carbon and phosphate availability. The formation of a long-lived Mn(III) oxide appears to depend on aqueous Mn2+ production and the relative proportion of electron donors and electron acceptors in the system. These real-time measurements identify mineralogical products during Mn(IV) oxide reduction, contribute to understanding the mechanism of various Mn(IV) oxide reduction pathways, and assist in interpreting the processes occurring actively in manganese-rich environments and recorded in the geologic record of manganese-rich strata.

Nucleation and growth of feitknechtite from nanocrystalline vernadite precursor

“…1). Steady-state was thus reached in less than 1 d of contact time, consistent with previous observations showing that feitknechtite is formed in less than 20 min (Johnson et al, 2016) and that sorption of Mn 2þ at the d-MnO 2 surface is completed within less than 1 s (Fendorf et al, 1993).…”

Anoxic photogeochemical oxidation of manganese carbonate yields manganese oxide

“…Indeed, Postma and Appelo (63) showed that reduction of manganite by sulfide and ferrous iron could reach completion within 10 h under ambient conditions. Johnson et al (64) showed rapid reduction of MnO x by sulfide and ferrous iron also within 10 h. In addition, microorganisms can also facilitate reduction of MnO x using organic matter. This is a major process of the Mn cycle in modern seawater.…”

Speciation and sorption of phosphorus in agricultural soil profiles of redoximorphic character

“…In soil, P generally is chemically bound within minerals (e.g., apatite) and organic substances (e.g., phospholipids), is sorbed to the minerals or organic surfaces predominantly as phosphate ion and occurs in the equilibrium soil solution as H 2 PO 4 − or HPO 4 2− . Under oxic conditions, phosphate ions might be sorbed to binding sites of clay minerals and/or Al, Fe and Mn (hydr)oxides with which they can form insoluble complexes (Lijklema 1980 ; Penn et al 2005 ; Johnson et al 2016 ). However, if controlled drains are closed, increased water content may lead to reducing conditions in soil.…”