Electronic structure of the non-equilibrium iron-deficient layer of hexagonal pyrrhotite

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

“…Natural polycrystalline hexagonal pyrrhotite Fe 9 S 10 from a Norilsk ore deposit contained about 2 wt.% impurity of pentlandite, (Fe,Ni) 9 S 8 , as described in detail elsewhere [33][34][35][36]. Plates of approximately 2 × 5 × 6 mm were cut from the massive minerals, abraded on silicon carbide paper, and then cleaned by wet filter paper to remove fine particles.…”

“…3). A narrow Fe 2p 3/2 peak at 707.3 eV, which is attributable to low-spin Fe(II) in the S-rich layer [33][34][35][36], emerges along with a smaller feature conventionally approximated by one maximum located at ∼708.5 eV from high-spin Fe(II)-S and possible Fe(III)-S species. Small changes of these contributions with varying photon excitation energies (when taking into account spectral resolution issues discussed above and some growth of a high-spin Fe(II)-S component) suggest that the state of iron remains nearly constant for profile depths down to ∼30 nm.…”

“…The chemical reactivity of iron sulfides in the environment and during mineral processing, as well as their electronic and optical properties strongly depend on the composition and structure of the real surfaces formed in natural and technological environ-ments. It is known from X-ray photoelectron spectroscopy (XPS) and other surface-sensitive techniques [2][3][4][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] that iron can be easily released from the lattice of these compounds, leaving non-equilibrium metal-deficient surface layers. The resulting surface sulfur enrichment is generally modest for oxidation-resistant pyrite, with intrinsic (fractured) pyrite surfaces possibly even being S-deficient [2][3][4][5][6][17][18][19][20][21][22][23][24][25][26].…”

“…The resulting surface sulfur enrichment is generally modest for oxidation-resistant pyrite, with intrinsic (fractured) pyrite surfaces possibly even being S-deficient [2][3][4][5][6][17][18][19][20][21][22][23][24][25][26]. In contrast, the metal depleted layer incorporates di-and polysulfide species and low-spin Fe(II) and can be as thick as several micrometers at pyrrhotite reacted in acidic solutions under certain conditions [27][28][29][30][31][32][33][34][35]; for example, Pratt and co-workers [30][31][32] have reported Auger depth profiles of several reacted pyrrhotites. It remains, however, unclear how the undersurface species alter with depth, in particular, because Ar + ion sputtering employed in many works could seriously affect the chemical state of Fe and S.…”

“…A number of XANES studies on iron sulfides have been reported previously [33,[43][44][45][46][47][48][49][50][51][52][53][54][55][56], but the difference between TEY and PFY Kedge spectra of air-oxidized and chemically etched materials has not been analyzed yet. Here, samples of each mineral (i.e., pyrite and pyrrhotite) polished in air were compared with those treated with an acidic ferric chloride solution to probe the effect of exposure to the leaching (etching) medium in hydrometallurgy and natural environments, and in materials science.…”