| Increased environmental pressures concerning SO{dollar}sb2{dollar} emissions have necessitated improved rejection of pyrrhotite, Fe{dollar}sb{lcub}rm 1-x{rcub}{dollar}S, in the processing of Ni/Cu ores. Froth flotation remains an important method for separating sulphide minerals from the gangue, and improved pyrrhotite rejection at this stage is desirable. A greater understanding of the surface chemistry of pyrrhotite and pentlandite, (Ni,Fe){dollar}sb9{dollar}S{dollar}sb8{dollar}, is required.; Detailed surface studies of pentlandite were undertaken using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and secondary electron microscopy (SEM). Analyses of pristine and oxidized millerite, NiS, were also carried out.; Near pristine pentlandite surfaces are characterized for the first time. XPS spectra reveal two S 2p doublets (at 161.4 and 162.2 eV) which arise from 4 and 5-coordinate S, respectively. Nickel and iron, occupying 4 and 6-coordinate sites in pentlandite, also result in two peaks in the Ni 2p{dollar}sb{lcub}3/2{rcub}{dollar} (852.8 and 853.8 eV) and Fe 2p{dollar}sb{lcub}3/2{rcub}{dollar} (706.7 and 707.5 eV) spectra. Pristine millerite gives rise to XPS peaks at binding energies of 161.7 eV (S 2p) and 853.1 eV (Ni 2p{dollar}sb{lcub}3/2{rcub}{dollar}) and oxidizes to give Ni(OH){dollar}sb2{dollar} and NiSO{dollar}sb4{dollar} surface species, when reacted in water and in air.; Pentlandite and pyrrhotite samples were reacted in solutions of pH 9.3, and the effects of potassium amyl xanthate (PAX), dissolved oxygen and diethylenetriamine (DETA) were studied. At pH 9.3, both minerals are covered with a thin FeOOH overlayer, and their surfaces are quite similar. Violarite, FeNi{dollar}sb2{dollar}S{dollar}sb4{dollar}, forms in the pentlandite subsurface, and at prolonged reaction times ({dollar}>{dollar}60 min), Ni oxidation products (Ni(OH){dollar}sb2{dollar} and NiSO{dollar}sb4{dollar}) begin to form and also accumulate in the subsurface. The paragenesis of pentlandite alteration products is discussed. When DETA is added, the rate of oxidation tends to increase. Oxidation is slowed, however, especially at the pentlandite surface, when PAX is added. Results indicate that pyrrhotite oxidizes-more rapidly than does pentlandite, especially when dissolved oxygen is in limited supply. At approximately 0.01-0.03 ppm dissolved oxygen, and in the presence of PAX, the pyrrhotite surface is heavily oxidized, while the pentlandite surface is almost entirely free of oxidation products. This remarkable result could prove an interesting avenue to explore for improving pentlandite/pyrrhotite separation by flotation. |
