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  Plectosphaerella cucumerina  DS2psM2a2 + 0.2 mM Mn2+

Plectosphaerella cucumerina DS2psM2a2 + 0.2 mM Mn2+

Metals + Manganese-Oxidizing Fungi

Manganese oxide minerals --which often control trace metal concentrations in the environment-- can undergo structural changes resulting in altered reactivities. Manganese-oxidizing fungi are very important in many natural and metal-polluted systems (such as coal mine drainage remediation sites). I am studying the effect of fungi on the stability of mycogenic manganese oxide precipitates and trace metal speciation, with the goal to better understand the controls on manganese oxide phase and structural transformations and trace metal behaviors over the long term.  


 Mn oxide samples at 5-BM-D at the Advanced Photon Source -ready to collect XAFS spectra!

Mn oxide samples at 5-BM-D at the Advanced Photon Source -ready to collect XAFS spectra!

Ni, Zn,  & Manganese Oxide Structures at Redox Interfaces (i.e., with coexisting Mn(II)aq & Mn(III/IV) solids)

At redox interfaces (i.e., subsurface environments, redoximorphic soils, marine & lacustrine sediment-water interfaces, aquifers, etc.), manganese in both reduced [i.e., dissolved Mn(II)] and oxidized [i.e., Mn(IV/III)--most stable as manganese oxide minerals] forms can coexist. I researched the effects of soluble Mn(II) on solid Mn(IV/III) oxide structures, as well as how such processes can impact trace metals.

  • Hinkle M.A.G., Becker K.G., Catalano J.G. (2017) “Impact of Mn(II)-Manganese oxide reactions on Ni and Zn speciation.” Environmental Science & Technology 51(6), 3187-3196. [link]
  • Hinkle M.A.G., Flynn E.D., Catalano J.G. (2016) “Structural response of phyllomanganates to wet aging and Mn(II).” Geochimica et Cosmochimica Acta 192, 220-234[link]

 Schematic showing an example of ternary complexes between Fe(II) and phosphate/sulfate on a hematite surface

Schematic showing an example of ternary complexes between Fe(II) and phosphate/sulfate on a hematite surface

Oxoanions + Fe(II)(aq)-Fe(III) Oxide Interactions

Fe(II) adsorption onto Fe(III) oxides can involve redox processes, resulting in Fe(II)-catalyzed Fe(III) oxide recrystallization. Oxoanions often alter cation adsorption onto mineral surfaces via ternary complexation, electrostatic interactions, or competitive adsorption processes. Focusing on sulfate and phosphate, two ligands commonly found in natural systems, we investigated their impact on Fe(II) adsorption onto hematite and goethite using a combination of wet chemistry, FTIR spectroscopy, and surface complexation modeling. I found that both phosphate and sulfate enhance Fe(II) adsorption onto both minerals, and that oxoanion adsorption mechanisms are altered in the presence of Fe(II), suggesting that oxoanions form ternary complexes with Fe(II) on Fe(III) oxide surfaces. Surface complexation modeling confirmed the formation of oxoanion-Fe(II) ternary complexes on Fe(III) oxides. These results indicate that phosphate and sulfate may affect processes associated with Fe(II)-catalyzed Fe(III) oxide recrystallization, such as trace metal repartitioning.


 Prepping XAFS samples for beamtime inside the anaerobic chamber

Prepping XAFS samples for beamtime inside the anaerobic chamber

Nickel + Oxoanions + Fe(II)aq-Fe(III) oxide Intearctions

As a natural extension of the oxoanion-Fe(II)(aq)-Fe(III) oxide research, we were interested in the effects oxoanions like phosphate and sulfate may exert on Ni repartitioning (i.e., the redistribution of Ni surface complexes and incorporated Ni) during Fe(II)-catalyzed Fe(III) oxide recrystallization. I found that the effects of phosphate and sulfate are distinct, with phosphate having a more substantial macroscopic impact on Ni uptake than sulfate. Interestingly, Fe(II)-catalyzed Ni repartitioning in goethite and hematite show distinct behavior, with Ni cycling through goethite being either permitted or enhanced by the oxoanions but through hematite being suppressed by both oxoanions (nearly inhibited in the case of phosphate). These results suggest that phosphate may have a particularly large effect on soils and sediments that experience variable redox conditions and are dominated by hematite (e.g., hydrothermal vents, waterlogged (sub)tropical soils).