Amorphous Fe-oxyhydroxide phases are important in many environmental systems. Their structure and stability are greatly influenced by the presence of light-element anions, which can coordinate to growing Fe-oxyhydroxide surfaces.  Our IR and XAS studies indicate that the stability of amorphous Fe-oxyhydroxides formed in the presence of Cl-, NO3-, SO42-, CO32-, and SiO44- vary significantly with the strongest effect in the case of Cl-, which delayed conversion to a crystalline phase until 245 days at pH 5.5.  We found that a significant fraction of Cl- associated with the amorphous phase exhibits inner-sphere binding with iron.  In comparison, CO32- destabilizes the amorphous phase within days at pH 8, while sulfate shows intermediate behavior.  The addition of SiO44- also stabilizes the amorphous phases, even at 170�M SiO44-.  Over time, the ligand concentrations in amorphous Fe-oxyhydroxides decrease, indicating that the ligand expulsion is tied strongly to the structural reorganization to the more crystalline phases.

Role of light-element anions on the stability of amorphous Fe-oxyhydroxides

245th National Meeting (2013)

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