| The surface characteristics of oxidized minerals are very important because oxidation usually takes place on sulfide mineral surfaces prior to flotation. In this thesis, the oxidation and wettability of chalcopyrite and pyrite in aqueous alkaline solutions were studied. The experimental results, using several electrochemical measurements, contact angles, flotation, UV spectra and SEM analysis, are presented. On the basis of these results, mechanisms for oxidation of these materials are proposed which involve layerwise growth of the oxidation products. A metal hydroxide layer may coat the mineral surface as a hydrophilic layer which is formed by hydrolysis of the metal ions released from the mineral. The release of metal ions from the mineral lattice produces a sulfur-rich layer beneath the metal hydroxide layer. This sulfur-rich layer is hydrophobic. Although the mechanisms for formation of layers on chalcopyrite are similar to those for pyrite, the conditions for their formation are quite different. In addition, the layer characteristics, in terms of reactivity, capacity, stability, hydrophobicity and porosity, of chalcopyrite are also different from those of pyrite. Properties of the surface layers affect both the continued oxidation and wettability. The results show that molecular oxygen plays a special role in the oxidation of chalcopyrite. The hydrophilic layer of metal hydroxy complexes/hydroxides can be removed by EDTA (Disodium ethylenediamine tetraacetate), so that the hydrophobic sulfur-rich layer can be exposed to the solution. A part of oxidation products on particles of sulfide minerals may be removed when preconditioned with quartz. If such conditions expose the sulfur-rich layer, collectorless flotation of chalcopyrite occurs. However, without the aid of EDTA, quartz cannot efficiently remove the iron-rich layer from pyrite and the flotation recovery is poor. In a carbonate solution, the ferrous carbonate precipitate grows from isolated sites on the surface of oxidized pyrite, exposing the sulfur-rich layer to the solution. Under these conditions, the surface of pyrite consists of hydrophobic and hydrophilic sites. |
