Scanning photoelectron microscopy studies of freshly fractured chalcopyrite exposed to O2 and H2O
Date
2014
Authors
Li, Y.
Chandra, A.P.
Gerson, A.R.
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Geochimica et Cosmochimica Acta, 2014; 133:372-386
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In order to better understand chalcopyrite oxidation processes surface speciation has been investigated using high-spatialresolution scanning photoelectron microscopy (SPEM). S2 , S2 2 and Sn 2 were detected on the chalcopyrite surface fractured under ultra-high vacuum, as have been observed by previous studies. No evidence for the formation of sulfoxy species was found on exposure of the surface to O2. Minor sulfoxy species were observed on exposure of surfaces to a mixture of O2/ H2O vapour, indicating H2O is necessary for their formation. Thus S oxidation may occur via two pathways. Under the condition examined S2 2 and Sn 2 species formation dominated and their formation did not require the presence of H2O. Species containing Fe(III)-O were detected on surfaces exposed to O2 only. On exposure to O2/H2O, the relative surface concentration of Fe(III)-S decreased significantly, due to the increased formation of species containing Fe(III)-O/OH/SO. It is possible that the mechanism of SO4 2 formation on chalcopyrite is similar to the electrochemical mechanisms proposed for pyrite involving attack by O2 at surface Fe sites resulting in formation of Fe-O species (cathodic reaction) and electron withdrawal from neighbouring surface sites (anodic reaction). This induces dissociation of H2O attached at adjacent Fe sites resulting in the release of H+, and nucleophilic attack of the resultant OH group onto the electron depleted surface S, to form SO moieties. The oxidation state of Cu on freshly fractured and moderately oxidised chalcopyrite surfaces examined in this study remains as +1, no evidence for the formation of Cu2+ was found.
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Crown copyright 2014 Published by Elsevier
Access Condition Notes: Postprint available 15 May 2016.