CHARACTERIZATION OF ARSENATE (ASV) AND ARSENITE (ASIII) ADSORPTION ONTO HEMATITE IN THE PRESENCE OF NATURAL ORGANIC MATTER (NOM)
Arsenate and arsenite adsorption onto hematite were studied at ca. pH 5.5 with Fourier transform infrared (FTIR) spectroscopy. Using attenuated total reflectance (ATR)-FTIR measurements, arsenate adsorption was detected by bands at ca. 910 cm-1 and ca. 869 cm-1. Arsenite adsorption was indicated by a band at ca. 847 cm-1. Upon contact with Suwannee River NOM, the arsenate and arsenite adsorption peaks decreased, consistent with less As adsorption occurring when NOM was present. ATR measurements, complemented by KBr pellet measurements, also showed a decrease in the stretching (ca. 2700-3600 cm-1 ), bending (ca.1250 1750 cm-1 ), and deformation (ca. 700 1000 cm-1 ) modes of hematite surface hydroxyls in the presence of AsV and AsIII. These results are consistent with AsV and AsIII forming adsorption complexes with hematite by replacing hematite surface hydroxyl groups. More detailed studies will be conducted in order to further elucidate the structure of these complexes. The relative importance of specific NOM functional groups with respect to their influence on arsenic adsorption will also be studied using model compounds such as salicylic acid and citric acid.