SURFACE-LAYERS IN BASE-METAL SULFIDE FLOTATION

Three surface-sensitive techniques, i.e. XPS (ESCA), scanning Auger microscopy and analytical scanning electron microscopy, have been used to study the surface layers on metal sulphides as single minerals, mixed minerals, synthetic ores and real ores from eight Australian concentrator operations. Validation of a sampling methodology to introduce a slurry, from the pulp after inhibition of oxidation, dissolution and removal of slimes, without air exposure of the mineral surfaces, to the instruments has shown that these procedures allow correlation of the measured surface chemistry with the process pulp. The techniques and methods are briefly reviewed with examples illustrating the correlation with process conditions. Evidence of the following characteristics of sulphide surfaces, derived from this study, is presented, namely: relatively thick carbonaceous, hydrophobic layers on some specific ores giving naturally flotable pyrite and chalcopyrite contrasted with normal hydrocarbon contamination of other sulphide surfaces; substantial hydroxide content in three forms as thin (approximately 5-80nm) layers, oxidised fine particles (approximately 0.1-5-mu-m) attached to larger sulphide particles and colloidal, spheroidal iron hydroxide floccs precipitated from solution; carbonate and sulphate species in surface layers; exposure of clean pyrite, chalcopyrite and pyrrhotite surfaces, metal deficient sulphide and polysulphide species; effects of E(h) variation on exposure of clean pyrite; partial removal of hydroxide and exposure of clean pyrite and chalcopyrite in xanthate addition and steam cleaning processes; and adsorption of Cu(I) on pyrite surfaces with possible implications for flotation by formation of specific xanthate complexes.