Abstract
AbstractEnargite surface reactivity in acidic ferric solutions simulating the acid mine drainage (AMD) environment has been investigated by X‐ray photoelectron (XPS) and X‐ray excited Auger electron spectroscopy (XAES) surface analysis. Natural enargite samples from a Peruvian mine with close to the nominal composition Cu3AsS4 have been analysed after cleavage and a 24 h exposure to 0.025 mol/l ferric acidic solutions.The results, based on the calculated modified Auger parameter α′, show that the chemical state of copper and arsenic in enargite does not change during immersion in acidic, oxidising solutions. The sulfur S 2p spectrum of enargite is characterized by two components, one at 162.0 ± 0.2 eV and the other at 163.5 ± 0.2 eV. The lower binding energy component (162.0 eV) is attributed to the sulfur atoms in enargite. Immersion does not change the chemical state of this compound. XPS/ARXPS measurements show the intensity of the higher binding energy component (163.5 ± 0.2 eV), located at the outermost surface of the reacted enargite, to increase after immersion in solutions. The chemical state plot suggests that this sulfur compound might be associated with the formation of a copper‐deficient enargite surface layer and not with elemental sulfur.Based also on the quantitative XPS determinations, the surface of the reacted enargite can be described as a layered structure: a thin copper‐deficient enargite layer (up to 0.7 nm) is formed on a slightly sulfur‐enriched enargite surface, the arsenic content remaining constant. Copyright © 2007 John Wiley & Sons, Ltd.
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