The thermal decomposition sequence of hydrous nickel-magnesium silicates from Colombia and Brazil was studied under air/Ar atmosphere from room temperature up to 750uC by differential scanning calorimetry-thermogravimetry followed by X-ray diffraction and scanning electron microscopy analyses. Differential scanning calorimetry curves of the samples obtained showed three endothermic peaks at 100, 250 and 600uC due to the release of free water, the dissociation of goethite and the release of crystalline water respectively. To determine the mineral species and microtexture, the ores were studied by scanning electron microscopy. Scanning electron microscopy-energy dispersive spectroscopy analyses showed that the ores are rich in Mg and Mg-Fe silicates, Cr spinel, Mn oxide, goethite and silica and exhibit complex alteration texture. Xray diffraction analyses of Colombia-2 and Mirabela (Brazil) after the experiments showed that the dehydroxylation produces an amorphous intermediate phase, which is supposed to be due to the exsolution of silica. However, Colombia-1 sample, which was confirmed to contain antigorite mineral, was observed to undergo dehydration and recrystallisation simultaneously.

The aim of the work reported here was to examine the effect of mineralogy on reducibility of three different nickel saprolite ores originating from Brazil (Mirabela deposit) and from Colombia (Cerro Matoso S.A. deposit) as well as find the optimal reduction conditions for the ores. The reduction experiments were carried out in a thermobalance furnace at constant temperatures 600, 750 and 900uC in H 2 /N 2 (72%/28%) gas mixture, followed with scanning electron microscopy (SEM-EDS) and chemical analyses. The results clearly indicate that the reducibility of the ores depends on the initial mineralogy of the ore and on the phases formed during heating, before the reduction stage. The presence of antigorite in Colombia-1 ore results in a simultaneous dehydroxylation and transformation of magnesium silicate to olivine and pyroxene during heating. Due to the recrystallisation, the degree of removable oxygen R t is decreased when increasing the temperature from 750 to 900uC. The low reducibility at 900uC was also confirmed by chemical analysis. Colombia-2 and Mirabela do not, however, contain antigorite and heating the samples resulted in formation of an easily reducible intermediate phase. Thus, the recrystallisation is not initiated at 750uC like in Colombia-1 and their R t values were also enhanced at 900uC. According to SEM-EDS results, a complex series of phase and microstructure changes has been observed along with the formation of Fe-Ni alloy particles.

The aim of this work was to explore the effect of mineralogy and gas reductant on the reduction of nickel laterites. Three different nickel saprolitic ores reduced by carbon monoxide were examined, and the results were compared with hydrogen reduction of the same ores. The reduction experiments were carried out in a thermobalance furnace which allows continuous measurement of mass change. The ores were reduced in CO/CO 2 (72% : 28%) at 750 and 900uC for 90 min. Chemical analysis was utilised to determine the degree of metallisation of the reduced pellets. It was found that the reduction rate and degree of removable oxygen at 750 and 900uC in CO/CO 2 was lower compared to reduction experiments in H 2 /N 2 (72% : 28%). The reducibility of the samples seems to depend on mineralogy and their modes of decomposition and recrystallisation. The results clearly indicate that using various reducing gases has an impact on the reduction behaviour and generation of metallics of nickel saprolitic ores.

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