Amorphous Fe-oxyhydroxide phases are common in the environment. Their structure and stability are greatly influenced by the presence of anions and cations acting as coordinating or substituting impurities.  Our IR and XAS studies indicate that the stability of amorphous Fe-oxyhydroxides formed in the presence of Cl-, SO42-, and CO32- vary significantly with the strongest effect in the case of Cl-, which stabilizes these phases for over a year 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 8.1, while SO42- shows intermediate behavior.  Over time, these ligand concentrations in amorphous Fe-oxyhydroxides decrease, indicating significant structural reorganization.  Different Al3+ concentrations alter the short-range order in amorphous Fe-oxyhydroxides and hinder their transformation.  These results are useful in predicting the long-term stability and reactivity of amorphous Fe-oxyhydroxides in the environment.

Role of selected anions (Cl-, SO42-, CO32-) and cations (Al3+) on the stability of amorphous Fe-oxyhydroxides

244th National Meeting (2012)

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