Recent work has shown that Mn(II) interactions with birnessite may have important environmental implications particularly in terms of Mn mineralogy.  At pH 7.5, Mn(II) induces transformation of birnessite into metastable feitknechtite and the more stable manganite polymorph. This investigation seeks to elucidate how these Mn(II) interactions affect Zn(II), an important trace metal whose geochemical cycling in soils and aquatic environments is affected by sorption reactions with naturally occurring Mn oxides. The dynamics of a ternary system containingaqueous Mn(II) and Zn(II) in the presence of a suspension of K-birnessite was examined at pH 7.5 under anoxic conditions. The 0.1 g/L suspension of birnessite was equilibrated with 50-400 �M of Zn for 2 days followed by injection of 1000 �M Mn(II). The system was sampled over a time period of 1-2 weeks and compared to binary systems that contained only aqueous Zn(II) or Mn(II) in contact with birnessite, and to control experiments that did not contain any added divalent metal. Solutions were monitored for dissolved Mn(II) and Zn(II) concentrations, while sample solids were analyzed by infrared (IR) spectroscopy, X-ray absorption spectroscopy (XAS), and scanning electron microscopy (SEM). Binary experiments containing Zn(II) and birnessite showed a maximum removal of approximately 300 �M Zn(II). Binary experiments containing Mn(II) showed a maximum removal of approximately 800 �M Mn(II). In the ternary systems, enhancedremoval of both Mn(II) and Zn(II) is observed relative to the binary samples. Zn K edge XAS data indicate major changes in the speciation of sorbed Zn in the ternary experiments as compared to the binary experiments, showing evidence for Zn incorporation into secondary Mn-oxidephases. These findings have important implications for predicting the fate of Zn(II) in environments that are characterized by both appreciable amounts of Mn and variable redox conditions.

Investigation of the synergistic effects of a ternary system containing Zn(II) and Mn(II) interacting with K-birnessite

247th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.