| Abstract |
Scorodite is an important mineral not only for arsenic (As) removal from industrial wastewaters but also in the mobility and final fate of As in waste rocks, contaminated soils and sediments, and mine tailings. Because of the mineral's high As-loading capacity and stability, numerous studies have been done to understand its formation. Unfortunately, most of these studies were limited to elevated temperatures (>70芒聙炉脗掳C), so the processes involved in scorodite formation under ambient conditions remain unclear. This study provides evidence of the catalytic effects of hematite on the formation of scorodite at 25芒聙炉脗掳C in a pyrite-rich natural geologic material. Scorodite peaks were detected in the XRD patterns of the leaching residues with and without hematite, but those in the former were stronger and more pronounced than the latter. These results suggest that the formation of scorodite was catalysed by hematite, a generalisation that is further supported by strong characteristic IR absorption bands of scorodite at 819 cm芒聙聯1 (As芒聙聯O bending vibration), 785 and 725 cm芒聙聯1 (As芒聙聯O stretching vibrations), and 2990芒聙炉cm芒聢聮1 (OH-vibration) as well as the distinct XPS binding energies of Fe(III)芒聙聯As (709.7芒聙炉eV), As(V)芒聙聯O (44.8, 44.31 and 43.7芒聙炉eV), O2芒聢聮 (530.5芒聙炉eV) and coordinated water (531.3芒聙炉eV) in scorodite. This phenomenon could be attributed to three possible mechanisms: (1) more rapid precipitation promoted by the 芒聙聹seeding芒聙聺 effect of hematite particles, (2) additional supply of Fe3+ from hematite dissolution under acidic conditions, and (3) enhanced oxidations of Fe2+ to Fe3+ and As(III) to As(V) on the surface of hematite. |
Mindanao State
University - Iligan Institute of Technology