Macroscopic and X-ray photoelectron spectroscopic investigation of interactions of arsenic with synthesized pyrite.

Interactions of arsenic with synthesized pyrite were investigated using macroscopic (solution phase experiments) and microscopic (X-ray photoelectron spectroscopic investigation) approaches. Arsenic removal by pyrite was strongly dependent on pH and arsenic species. Both arsenite (As(III)) and arsenate (As(V)) had a strong affinity for the pyrite surface under acidic conditions, but As(III) was more effectively removed than As(V). A BET isotherm equation provided the best fit to arsenic removal data, suggesting that surface precipitation occurred at a high arsenic/pyrite ratio. The addition of competing ions did not substantially affect the ultimate distribution of arsenic between the pyrite surface and the solution, but changing the pH affected arsenic stability on pyrite. X-ray photoelectron spectroscopy (XPS) revealed that under acidic conditions, arsenic was removed by reaction with pyrite to form solid phases similar to As2S3 and As4S4. However, under neutral to alkaline conditions, arsenic was removed by sorption and precipitation to form solid phases that are similar to FeAsS and As2S3/As4S4.