Photoelectron core levels for enargite, Cu₃AsS₄

Abstract

The mineral chemistry of enargite surfaces and near-surfaces prepared by fracture within an ultrahigh vacuum are investigated using XPS and synchrotron radiation XPS (SRXPS). The purpose of the study is to identify surface core-level line positions in high-resolution photoelectron spectra. The XPS spectra obtained using monochromatic Al Ka radiation show that there are near-identical monosulphide line positions in S 2p spectra for the As-S and Cu-S bonds in enargite. The SRXPS spectra for sulphur are remarkably similar to the XPS spectra for sulphur, showing that there is minimal difference in the chemical environment between sulphur atoms at the surface and in the mineral matrix. The Cu 2p XPS data have only cuprous contributions and a minor surface contribution. The surface Cu contribution is observed as a high-binding-energy tail in the Cu 2p 3/2 spectrum. The As 3d data for both XPS and SRXPS show contributions from arsenic atoms at the surface and in the bulk mineral matrix. The surface contribution is distinct and is found 1 eV below the bulk contribution. The results of the study suggest that, following fracture, the enargite surface is reorganized in such a manner that the surface is characterized by protrusions of individual arsenic atoms.

The oxidative dissolution of arsenopyrite (FeAsS) and enargite (Cu3AsS4) by Leptospirillum ferrooxidans

“…2c and Table 3). This is interpreted as monosulphide sulphur (S 2À ) in enargite and is in agreement with enargite analysis by Pratt (2004). A second doublet is required to fit the high binding energy tail at 163.4 ± 0.2.…”

“…The Cu 2p (3/2) peak is positioned at 932.5 ± 0.6 eV with a FWHM of 1.1 eV. The shape and position of this peak are similar to those reported for copper in the cuprous state (Fullston et al, 1999;Pratt, 2004), so is therefore interpreted as Cu(I) bonded to sulphur. On both the high and low binding energy sides of this peak it was not possible to fit the data without under-fitting with respect to the background applied (Fig.…”

“…Peak parameters are given in Table 3. This spectrum is characterised by a minor doublet at 42.1 ± 0.2 eV representing As in the enargite surface and a major doublet at 43.2 ± 0.0 eV interpreted by Pratt (2004) as As in the bulk enargite matrix. Although the binding energy is $3 eV lower than reported for oxygen-bearing As(V) species, As in enargite is formally As(V) (Pratt, 2004).…”

“…Inorganic analytical studies of the surfaces of arsenopyrite and enargite are numerous, particularly using X-ray photoelectron spectroscopy (XPS) (Buckley and Walker, 1988-89;Nesbitt et al, 1995;Fantauzzi et al, 2002;Pratt, 2004). These studies have focused on the inorganic oxidation of mineral surfaces by a variety of reactants chosen to simulate natural acid mine drainage environments.…”

Arsenic Chemistry

“…Substitutions between copper, iron, and zinc are also likely. Unlike most other metallic arsenosulfides, the arsenic in enargite is As 5+ (Pratt, 2004). That is, enargite is an orthorhombic (Pnm2 space group) thioarsenate, where each arsenic atom is coordinated with four sulfur atoms (AsS 4 3− ) (Castro and Baltierra, 2005).…”