XPS, DRIFTS, UV spectroscopy and HPLC were used to investigate the nat
ure and spatial distribution of oxidized superficial phases present on
pyrite surfaces. Two pure pyrites with different arsenic contents wer
e used. The surface of the first sample (As = 0.018%) is covered with
an important three-dimensional heterogeneous oxidized phase (Fe2(SO4)3
, Fe(OH)3, FeO) in equilibrium with two two-dimensional phases (metast
able polysulphide (S5S2-) and elemental sulphur (S8)). The superficial
phases present at the surface of the second pyrite (As = 0.309%) have
the same composition. However, their extension is mainly two-dimensio
nal with lower amounts of polysulphide (S5S2-) and elemental sulphur.