SURFACE CHARACTERIZATION OF PENTLANDITE, (FE,NI)(9)S-8, BY X-RAY PHOTOELECTRON-SPECTROSCOPY

Near-pristine surfaces of natural pentlandite have been characterized for the first time by X-ray photoelectron spectroscopy (XPS). The Fe 2 p, Ni 2p, S 2p and O 1s spectra are discussed, The main feature of int erest is found in the S 2p spectrum where two major doublers are found , one with a S 2p(3/2) binding energy of 161.44 eV and the other at 16 2.19 eV. These doublers are interpreted as being due to sulphur in a 4 -coordinate environment and a 5-coordinate environment, respectively, We have obtained a ratio of 1:2.5 for these two species, in reasonable agreement with the theoretical ratio of 1:3 predicted from the pentla ndite structure. Natural pentlandite samples have been exposed to de-i onized water for periods of 1.5 and 6 h. The pentlandite surfaces were oxidized to give surfaces that were rich in iron oxyhydroxide species and depleted in nickel and sulphur. (C) 1997 Elsevier Science B.V.