CHARACTERIZATION AND SURFACE REACTIVITY OF CORUNDUM IN AQUEOUS NACL MEDIA

The mineral-water interface plays an important role in geochemical processes such as ion adsorption and desorption, redox reactions, and the mobility and transport of metals and contaminants. The present study examines the mineral-water interface reactivity of corundum (α-Al₂O₃), to better understand the role of aluminum-oxide phases in natural aqueous environments. Corundum was selected for study because it is stable over a broad range of environmental conditions. In this study 6 α-Al₂O₃ phases were characterized extensively, then the surface charging behavior of the samples were evaluated by potentiometric titration. Characterization included BET surface area measurements, XRD, electron microscopy imaging (i.e, SEM and TEM), thermogravimetric analysis, and digestion for LA-ICP-MS analyses. Characterization confirmed that the samples were pure (> 99 %), crystalline a-Al₂O₃. The particle morphology was platy, and the surface area varied from 0.37 to 9.75 m²/g. The potentiometric titrations were performed at 25 ºC (± 0.1 ºC), in NaCl media, and ionic strengths from 0.03 to 0.3 m. All titrations were performed from acid to base, over an extensive pH range of 2.5 to 10. The surface charging behavior of all samples was similar. The pH of zero net proton charge (pH_znpc) for the samples was approximately 9.0. A notable feature of all experimental results was an inflection in the slope of the titration curves near pH 5. This presentation will highlight the interface reactivity of α-Al₂O₃ surface, which may influence the sequestration and degradation of various aqueous contaminants.