Due to their high reactivity, iron and aluminum (hydr)oxides present in natural and engineered systems often dictate contaminant fate and transport in the environment. As a result, numerous studies have examined the formation and reactivity of these phases and highlighted the impact of background water chemistry. For example, previous studies have documented effects of adsorbing and complexing ligands on both the rates and extent of precipitation and adsorption processes. In this study, we consider the adsorption and co-precipitation of multiple anions (e.g., F-, SO42-, and Cl-), heavy metals (e.g., As(III) and As(V)), and natural organic matter (NOM) to amorphous iron and aluminum oxides. The effects of these ligands on the morphology of the precipitates and their adsorption properties is explored by characterizing the physical floc characteristics (size, volume, etc.) and the ligand-oxide metal bonding environment. Batch reactor experiments (jar tests) were performed by simultaneously adding Al or Fe salt and one or more of the selected ligands to the reactor, adjusting the pH to promote precipitation, and allowing amorphous precipitates to form over short periods of time (i.e., 20 minutes). Different combinations of ligands were tested to study their interactions within the system. X-ray photoelectron spectroscopy (XPS) and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) were utilized to identify the ligand binding mechanisms and a Coulter counter was utilized for characterizing floc diameter and volume. The results showed varying impacts of the ligands on physical floc characteristics and reactivity of the amorphous phases. For example, the presence of fluoride reduced floc diameter and increased aluminum and iron bond energies. Both competition and co-adsorption affected removal of particular ligands. For example, the presence of NOM had opposite effects on adsorption of As(III) and As(V). These results were consistent with differences in As binding to the amorphous aluminum hydroxide surface.

Ligand effects on amorphous iron and aluminum hydr(oxide) precipitate characteristics

253rd National Meeting (2017)

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