Interactions of aqueous Mn(II) with hexagonal birnessite were examined in the pH range 5.5-8.5 under anoxic and oxic conditions.  Transformation of birnessite into feitknechtite is observed at pH 6.5-8.5. Subsequent transformation of metastable feitknechtite into other Mn-phases is influenced by pH and Mn(II) concentration.  Analysis by ATR-FTIR, XRD, XANES and EXAFS demonstrates the formation of hausmannite at pH 8.0-8.5 and formation of manganite at pH<8.0, particularly at higher Mn(II) inputs.  Intermediate Mn(II) inputs exhibit a mixture of phases.  At pH<6.5, interaction with Mn(II) leads to modification of the initial birnessite substrate through adsorption and oxidation of  Mn(II), but does not cause bulk mineralogical transformation.  Oxic experiments show enhanced removal of Mn(II) solution at higher pH, indicative  of surface-catalyzed oxidation of Mn(II) by O2. The  mechanisms operational in these systems may have strong implications for the fate of pollutants and toxins, such as trace metals, commonly found in the environment.

Effects of pH on Mn(II) interactions with birnessite under oxic and anoxic conditions

245th National Meeting (2013)

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