The structure of amorphous copper sulfide precipitates: An X-ray absorption study

• Published in: Geochimica et cosmochimica acta Vol. 61; no. 10; pp. 2023 - 2036
• Main Authors: Pattrick, R.A.D., Mosselmans, J.F.W., Charnock, J.M., England, K.E.R., Helz, G.R., Garner, C.D., Vaughan, D.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.05.1997
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(97)00061-6

X-ray absorption (XAS) and X-ray photoelectron spectroscopy (XPS) analysis of copper sulfide precipitated from aqueous solution at ambient temperatures reveals the existence of a metastable primitive structure that ages to a structure with the characteristics of amorphous covellite; XAS provides direct structural information on the structure of these amorphous copper sulfides. Extended X-ray absorption fine structure (EXAFS) analysis of the primitive structure demonstrates the presence of disulfide (S 2-groups) and a Cu S interaction of 2.8Å: the latter is not found in covellite. Copper K-edge X-ray absorption near-edge structure (XANES) indicates the dominance of 3- over 4-coordinate Cu in the primitive phase, while Cu L 3-edge spectra reveal only Cu(I) to be present in all precipitates formed. XPS data confirm the presence of only Cu(I) and reveal that three types of S are present. Upon ageing, the primitive structure transforms to one with the characteristics of covellite, and this transformation involves the reordering of the S 2- and Cu 3S CuS 3-layers. Development of the primitive phase from either a wurtzite-like structure or planar Cu 3S CuS 3-layers is possible, with the structural evolution driven by the antipathy of Cu(II) for tetrahedral coordination and anomalous electron densities in the metastable structures.