Text

theses

This dissertation examines Mn(II)-birnessite interactions to improve understanding of the geochemical cycling of manganese, their influence on other elemental cycles, and the fate and solubility of trace metals through three studies that determined: (1) the influence of pH on Mn(II)-birnessite interactions under oxic and anoxic conditions, (2) how Zn(II) impacts Mn(II)-birnessite interactions, and (3) how Ni(II) impacts Mn(II)-birnessite interactions. UV-Vis spectroscopy and flame AAS were used in conjunction with XRD, XAS, ATR-FTIR and SEM to determine changes in solution chemistry concomitant with the reaction substrate in batch sorption experiments. Birnessite reacted at pH < 7.0 exhibited no bulk mineralogical transformation products. At pH 7.0-8.5, reaction with Mn(II) under anoxic conditions caused reductive transformation of birnessite into different end products contingent upon pH, the concentration of Mn(II) and/or the presence of either Zn(II) or Ni(II). For binary Mn(II)-birnessite systems, formation of feitknechtite (β-MnOOH) and manganite (γ-MnOOH) were observed at pH 7-8. At pH 8.0-8.5, Mn(II)-birnessite interactions produced hausmannite (Mn3O4). In oxic systems, reductive transformation of birnessite is complemented by surface catalyzed oxidation of Mn(II) by O2. Mn(II) was found to compete for sorption sites with Zn(II) at pH 6.5. At pH 7.5, Zn(II) and Mn(II) sorption were observed to be enhanced relative to the corresponding experiments where only one aqueous divalent metal was present. The speciation of Zn(II) was different than at pH 6.5 and XAS results in combination with XRD data demonstrate formation of spinel Zn(II)1-xMn(II)xMn(III)2O4. When Mn(II) is present in systems containing Ni(II)-birnessite at pH 6.5, Ni(II) edge-sharing surface complexes form. At pH 7.5, Mn(II) has a distinct impact on Ni(II) speciation. Transformation of Ni(II)-birnessite, following introduction of Mn(II), to a feitnechtite-like phase containing Ni(II) was evident by XRD and ATR-FTIR analyses; further conversion to manganite was inhibited. XAS, FTIR, and XRD analyses suggest that Ni(II) is incorporated into the feitknechtite-like structure. The results of this dissertation suggest that aqueous Mn(II) is an important control on the mineralogy and reactivity of natural Mn-oxides, as well as the fate and solubility of trace metals, particularly in aqueous geochemical environments with neutral to alkaline pH values.

ETD_6954

Ph.D.

Includes bibliographical references

by Joshua Lefkowitz

doi:10.7282/T3TX3HM8

ETD doctoral

The author owns the copyright to this work.