Magnesia mixture as a regulator in the separation of pyrite from chalcopyrite and arsenopyrite

Abstract The aim of this paper is to find an effective method for the separation of the undesirable constituents, namely, chalcopyrite and arsenopyrite from pyrite used for the production of H 2 SO 4 . A new effective method is developed for co-depressing chalcopyrite with arsenopyrite by AsI 3 , followed by the addition of magnesia mixture. This method has been shown to be based on the fact that iron sites exist in the three minerals, whereas copper and arsenic sites exist only in chalcopyrite and arsenopyrite, respectively. This is coupled with the ability of both Cu(I) and Cu(II) to precipitate As(III) in the form of insoluble copper arsenides, namely Cu 3 As, Cu 3 As 2 . In contrast, neither Fe(II) nor Fe(III) form stable arsenides. Consequently, As 3+ ions are selectively adsorbed onto the surface of chalcopyrite. The facility for oxidizability of As(III) is well known and hence it adsorbs oxygen from the pulp and changes to As(V) of higher valency and smaller size, with ionic potential over 10. Accordingly, it yields a stable complex anion with covalent bonding, namely, [AsO 4 ] 3− . These newly created arsenate sites on the surface of chalcopyrite, as well as the corresponding original arsenate sites on the surface of arsenopyrite combine with magnesia mixture to form cations leading to the formation of tightly abutting strongly hydrophilic layers of … AsO 4 NH 4 Mg.6H 2 O. The spread of this hydrophilic film on arsenopyrite and chalcopyrite surfaces leads to the screening of their surfaces, making them difficult of access for the collector, ethyl xanthate. Since the pK a of xanthic acid occurs at pH below 3, xanthate species predominate at pH above 8 and are adsorbed selectively on the pyrite surface in sufficient quantity for its selective flotation and hence for its separation to take place in the pH range 8–9.