Abstract: This paper studies mineralogical phase transformations of Indonesia nickel laterite ores during roasting. The influence of pre-roasting temperature on the degree of gas(V (CO) : V (O₂)=50 : 50)reduction is also investigated. Different factors affecting reduction of the laterite ores are tested and analyzed with various means such as differential scanning calorimeter thermal gravimetric (DSC/TG), Brunauer Emmett Teller (BET) specific surface area analysis, X-ray diffraction (XRD) and scanning electron microscope (SEM).The results show that, during the roasting process, goethite is dehydrolyzed at about 300°C. It is then transformed to hematite and serpentine decomposes around 600~700°C leading to formulation of olivine if agglomerating is at higher temperature. Nickel and iron metallization rate increases with the increasing pre-roasting temperature by using gas mixture (V (CO) : V (O₂)=50 : 50). The highest reduction rate can reach 86.81% with the sample being roasted at 700°C. If the calcination temperature exceeds the olivine formation temperature, the nickel metallization rate declines to 66.73%.

Key words: nickel laterite ore, phase transformation, preheating