| The mechanisms of roasting, reduction and smelting of Ni-Cu concentrates were investigated. This was done by: (i) quantifying the variation in chemical composition of the concentrate particles during roasting, (ii) quantifying the reactivity profiles to air and CO;The behaviour of pyrrhotite, pentlandite and chalcopyrite particles in a fluid bed roaster are discussed. The rate of roasting under industrial conditions is much higher than under laboratory conditions. The oxidation rate of pyrrhotite is greater than that of pentlandite and chalcopyrite. The rate of partial roasting of concentrate particles may be limited by the diffusion of oxygen through the oxide rims which were formed upon oxidation.;Coke gasification rates were unified in a single relationship. The differences in the rates of coke-CO;Reduction and smelting tests of calcine/coke mixtures were carried out using (i) nonisothermal and isothermal thermogravimetric methods, and (ii) continuous measurements of the SO;The variations in chemical composition of Ni-Cu calcines roasted at various degrees of sulphur elimination were successfully quantified by implementing image analysis techniques. The results are in good agreement with those of the chemical analysis.;Laboratory simulation of the reduction and smelting process and characterization of the fusion zone samples allowed the formulation of schematic models representing the process mechanisms. The sequence of events comprising the interplay of oxysulphide formation, oxysulphide reduction, matte coalescence, matte/slag separation and slagging reactions leading to changes in the reduction medium was analyzed. Trends in variations of the reduction mechanisms when using mixtures of 65 and 80% roast calcines with different coke sizes were discussed. |
