Thermal chemistry of H₂S and H₂O on the (100) plane of pyrite; unique reactivity of defect sites

Abstract

The interaction of a natural face of FeS 2 (100), cleaned in ultra-high vacuum (UHV), with H 2 O and H 2 S has been investigated with X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and the photoemission of adsorbed xenon (PAX). PAX is sensitive to the short-range order of the surface and allows the effects of defects on the surface reactivity of FeS 2 (100) to be studied. PAX results suggest that both H 2 S and H 2 O bind most strongly to defect sites that we propose are, at least in part, sulfur anion vacancy sites. Whereas the majority of H 2 O adsorbate desorbs from these sites in the temperature interval of 200-300 K, H 2 S dissociates upon heating to 500 K into adsorbed surface hydrogen, S, and SH. This dissociation occurs on defect sites that then release part of the dissociation fragment, which is thought to be surface hydrogen, onto other regions of the pyrite surface that are proposed to be stoichiometric FeS 2. Heating to 600 K causes further reaction of S containing dissociation fragments with sulfur-deficient sites to form new surface sites that resemble FeS 2. The results also suggest that surface hydrogen dissolves into the pyrite bulk upon heating to 600 K.

Uptake of uranium and trace elements in pyrite (FeS2) suspensions

“…The low pH PZC suggests that sulphide groups, not Fe-bound hydroxyls, control then surface charge (Sun et al, 1991;Dekkers and Schoonen, 1994;Vaughan et al, 1997;Bebié et al, 1998;Guevremont et al, 1998;Rosso et al, 1999). This assumption is supported by the S-enrichment observed for pyrite surfaces for all common {1 0 0}, {1 0 1} and {1 1 1} crystallographic orientations (Elestinov et al, 2000).…”

Pyrite (FeS2) oxidation: A sub-micron synchrotron investigation of the initial steps

“…Surface defect sites that contain Fe dangling bonds (S deficient) have been widely suggested to play a critical role during the initial stages of the oxidation process (Rosso et al, 1999a,b;Guevremont et al, 1997Guevremont et al, , 1998bKendelewicz et al, 2004). Indeed, non-stoichiometric S sites (such as S 2À ) have been shown to be the most reactive of all surface S species (Schaufuß et al, 1998a).…”

“…What is known is that pyrite oxidation tends to occur upon exposure to atmospheric gasses such as O 2 and H 2 O and that on exposure to the atmosphere S 2À is the most reactive of the sulfur species followed by S 2 2À (surface) and S 2 2À (bulk) (Schaufuß et al, 1998b). Fresh pyrite surfaces have also been shown to undergo different degrees of oxidation upon exposure to either O 2 or H 2 O with oxidation being most aggressive when both these gases are present together (Guevremont et al, 1998b;Kendelewicz et al, 2004;Nesbitt and Muir, 1994;Schaufuß et al, 1998a). Sulfate has been recognised as the final product of atmospheric pyrite oxidation; however, there is disagreement as to the existence and role of S and Fe intermediates and products.…”

Functionalisation of Colloidal Transition Metal Sulphides Nanocrystals: A Fascinating and Challenging Playground for the Chemist

“…This has been ascribed to the difference between pyrite surfaces obtained by crystal fracturing and those grown and cleaned in vacuum. In fact, whereas the former is found to react with O 2 [188], the latter is non-reactive [189][190][191]. Arsenic is a common contaminant of pyrite, which may rise concerns about the environmental impact of this mineral.…”