X-Ray Photoelectron Spectroscopic Investigation of Interactions of Arsenic with Microwave Synthesized Pyrite as a Function of pH

Abstract

Interactions of arsenic with synthesized pyrite were investigated using X-ray photoelectron spectroscopy (XPS) and found to be strongly affected by pH. Under neutral to alkaline conditions, a defective pyrrhotite-like Fe-S phase that resulted from microwave irradiation during synthesis of pyrite dissociated from bulk pyrite to form small particles with a more oxidized surface. Larger particles (bulk pyrite) had surfaces that were almost identical with those of pyrite reacted under acidic conditions. Arsenic was removed by precipitation of an As₄S₄-like phase during reaction with pyrite under acidic conditions. However, under neutral to alkaline conditions, arsenic was found on the surface as As(III)-O and As(V)-O surface complexes as well as an As₄S₄-like precipitate. As pH increased, arsenic removal and formation of an As₄S₄-like precipitate decreased, whereas removal and formation of As(III)-O and As(V)-O surface complexes increased. Under alkaline conditions, a FeAsS-like phase was also detected.