Effect of sulphur addition on roasting reduction of saprolitic nickel ores in CO/CO2 gas mixture

The objective of the work presented here was to examine the effect of sulphur on formation of high temperature recrystallised phases and further on reducibility of saprolitic nickel ores. The ores blending with FeS2 were first heated up to 1300 degrees C to investigate the changes that might happen upon heating. As a result of sulphur addition, the exothermic peak, which is evidently associated with crystallisation of new phases, changed in size compared to ores without sulphur addition. In addition, the dehydration and recrystallisation of minerals was also observed to begin earlier, when sulphur is added in the ores. Additionally, the ores were reduced in CO/CO2 atmosphere at temperatures 750 and 900 degrees C, in order to determine the effect of sulphur and temperature on the reducibility. Although sulphur prevented the formation of difficult reducible olivine, as well as pyroxene phases in Colombia-2 and Mirabela, the degree of removable oxygen was not enhanced when increasing the temperature from 750 to 900 degrees C. This is due to low reduction of iron oxides to metalic iron at 900 degrees C. The beneficial effect of sulphur on metallisation degree of the ores was observed by comparison of these results with the experiments carried out with the pellets without sulphur addition. The results obtained in this study clearly indicate that the reduction of saprolitic nickel ores appears to be strongly dependent on the characteristics of the starting materials, amount of additive used and the process conditions.