REVIEW: ADSORPTION OF IONS AND MOLECULES TO SOLID SURFACES IN CONNECTION WITH FLOTATION OF SULPHIDE MINERALS

Valuable sulphide minerals are separated and concentrated from the crude ore by means of flotation. One fundamental step in this process is the selective hydrophobation by a collector of certain sulphide mineral surfaces. The most commonly used collectors are alkylxanthate (O-alkyldithiocarbonate) ions, R-O-CS2 −, O-O-dialkyldithiophosphate ions, (RO)2-PS2 −, and N,N-dialkyldithiocarbamate ions, R2N-CS2 −. The adsorption mechanisms of these collectors on the sulphide minerals sphalerite (ZnS), galena (PbS), chalcocite (Cu2S), acanthite (Ag2S), covellite (CuS), chalcopyrite (CuFeS2), pyrite (FeS2), marcasite (FeS2), pentlandite (Fe, Ni)9S8), pyrrhotite (FeS1−x), troilite (FeS), millerite (NiS), molybdenite (MoS2), realgar (AsS), orpiment (As2S3) and arsenopyrite (FeAsS). A strong correlation between the structure of the sulphide mineral and the adsorption mechanism is found. The studied collectors are adsorbed to the mineral surface according to one or two of the following adsorption mechanisms: a) the collector is oxidized to a very hydrophobic compound physisorbed to the surface, b) the mineral surface is oxidized and the metal ions are dissolved from the surface, which in presence of collector precipitates on the mineral surface as a hydrophobic solid metal collector salt, and c) the collector forms surface complexes chemisorbed to specific atoms/ions in the mineral surface through covalent interactions. The crystal structure of sulphide minerals and some metal collector salts are presented. The most commonly used techniques to study ions and molecules adsorbed on solid surfaces are presented and evaluated.