The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace Elements: Implication for Soil Remediation

Bujdoš

Polák

et al. 2021

JoF

This work aimed to examine the bioleaching of manganese oxides at various oxidation states (MnO, MnO·Mn2O3, Mn2O3 and MnO2) by a strain of the filamentous fungus Aspergillus niger, a frequent soil representative. Our results showed that the fungus effectively disintegrated the crystal structure of selected mineral manganese phases. Thereby, during a 31-day static incubation of oxides in the presence of fungus, manganese was bioextracted into the culture medium and, in some cases, transformed into a new biogenic mineral. The latter resulted from the precipitation of extracted manganese with biogenic oxalate. The Mn(II,III)-oxide was the most susceptible to fungal biodeterioration, and up to 26% of the manganese content in oxide was extracted by the fungus into the medium. The detected variabilities in biogenic oxalate and gluconate accumulation in the medium are also discussed regarding the fungal sensitivity to manganese. These suggest an alternative pathway of manganese oxides’ biodeterioration via a reductive dissolution. There, the oxalate metabolites are consumed as the reductive agents. Our results highlight the significance of fungal activity in manganese mobilization and transformation. The soil fungi should be considered an important geoactive agent that affects the stability of natural geochemical barriers.

Section: Discussionsupporting

confidence: 56%

Bioleaching of Manganese Oxides at Different Oxidation States by Filamentous Fungus Aspergillus niger

Bujdoš

Polák

et al. 2021

JoF

“…Since its discovery in 1956 at Birness, Scotland, the layered manganese oxide birnessite has been recognized as the most abundant manganese oxide in the Earth surface environment and a key reactive mineral that regulates the geochemical cycling of trace metals. , Metal-containing birnessite has been documented in soils, mineral and rock coatings, sediments, and marine ferromanganese crusts and nodules. − Birnessite also features promising electrochemical energy storage performance and catalytic capabilities when fabricated under appropriate conditions, − and its high sorption capacity can be used in waste water treatment. − Birnessite is a phyllomanganate, meaning a layered compound composed of edge-sharing Mn(IV)O 6 octahedra, with ideal chemical formula MnO 2 . However, birnessite is never stoichiometric.…”

Section: Introductionmentioning

confidence: 99%

Nature of High- and Low-Affinity Metal Surface Sites on Birnessite Nanosheets

Manceau

Steinmann

2021

ACS Earth Space Chem.

Birnessite nanosheets (δ-MnO2) are key reactive nanoparticles that regulate metal cycling in terrestrial and marine settings, yet there is no molecular explanation for the sorption selectivity of metals which controls their enrichment. This fundamental question was addressed by optimizing the structure of the Ni, Cu, Zn, and Pb surface complexes on δ-MnO2 and by calculating the Gibbs free energy change (ΔG) of the sorption reactions with density functional theory. The sorption selectivity follows the order Pb > Cu > Ni > Zn, in good agreement with experimental data. Cu, Ni, and Zn bind preferentially to layer edges at low surface coverage forming double-edge-sharing (DES) complexes, whereas Pb binds extensively with high selectivity over the three transition metals to both layer edges (DES bonding) and to basal planes forming triple-corner-sharing (TCS) complexes. Pb has similar affinity for the DES and TCS sites at pH 5 and a higher affinity for the TCS sites at circumneutral pH. The Pb DES and TCS complexes are both dehydrated at the δ-MnO2-water interface and feature a trigonal pyramidal geometry with three surface O atoms. The high stability of the two new complexes arises from the hybridization between the Pb 6s/6p and the O 2p states, forming a strongly covalent Pb-O/OH bond at the δ-MnO2 surface. The quantum chemical results provide mechanistic and energetics insight on metal uptake on δ-MnO2 that extends what extended X-ray absorption fine structure (EXAFS) spectroscopy alone can provide.

“…The radicals undergo rearrangement, and manganese oxides could further oxidize more stable intermediates [145]. Thus, the transformation of organic compounds can lead to a depletion of manganese oxides of higher valences, and the concentration of dissolved Mn(II) increases simultaneously [146].…”

Section: The Role Of Manganese In Geochemical Barriersmentioning

confidence: 99%

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact

Vojtková

et al. 2023

IJMS

Manganese oxides are considered an essential component of natural geochemical barriers due to their redox and sorptive reactivity towards essential and potentially toxic trace elements. Despite the perception that they are in a relatively stable phase, microorganisms can actively alter the prevailing conditions in their microenvironment and initiate the dissolution of minerals, a process that is governed by various direct (enzymatic) or indirect mechanisms. Microorganisms are also capable of precipitating the bioavailable manganese ions via redox transformations into biogenic minerals, including manganese oxides (e.g., low-crystalline birnessite) or oxalates. Microbially mediated transformation influences the (bio)geochemistry of manganese and also the environmental chemistry of elements intimately associated with its oxides. Therefore, the biodeterioration of manganese-bearing phases and the subsequent biologically induced precipitation of new biogenic minerals may inevitably and severely impact the environment. This review highlights and discusses the role of microbially induced or catalyzed processes that affect the transformation of manganese oxides in the environment as relevant to the function of geochemical barriers.