Amorphous and poorly crystalline phases are common and influence the biogeochemistry and transport of contaminants and nutrients in the environment. We examined the stability of amorphous ferric oxides formed in the presence of different anionic and cationic impurities using different spectroscopy (X-ray absorption, X-ray photoelectron, and FT-IR spectroscopies), and microscopy (TEM) methods. We also used calorimetry to evaluate the relative stabilities of these impurity containing phases. Our study showed that the nucleation of goethite from the amorphous ferric oxides was significantly influenced by the nature of impurity ion present during Fe(III) hydrolysis: faster nucleation of goethite at pH 5.5 in the case of SO42- and slower in the presence of Cl- among the examined anions. However, an increase in goethite fraction in the solid phase was greater in the case of NO3- and Cl-. At pH 8.1, we found the opposite effect and the amorphous ferric oxide with SO42- took longer time to nucleate goethite. Although strongly complexing ligands, such as phosphate, were shown to influence the nucleation and growth of minerals, our results suggest that even weakly complexing ions can play an important role in these processes. In the presence of Al3+, we found that the nucleation of goethite was not observed at Al concentrations studied in 1300 days. The differences in these patterns are attributed to the nature of interactions between these anions and cations with Fe-polyhedra. A discussion of these interactions and how they influence the nucleation of goethite will be presented.

Impact of anionic and cationic impurities on the nucleation and growth of nano-Goethite

253rd National Meeting (2017)

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