Mineralogical transformation and Ni enrichment through reduction roasting of limonite ore from the Tinanggea area, South Konawe, Southeast Sulawesi

Abstract

Abstract A limonite ore sample from the Tinanggea Area of Southeast Sulawesi has been investigated via the reduction roasting method using coal as a reducing agent. This study aimed to discover the mineralogical and chemical characteristics of the ore and analyze the effect of heating temperatures and dosages of reductants on mineral transformation and the upgrading of nickel. Mineralogical and chemical characterization of the sample was performed using optical microscopy, X-ray diffraction (XRD), and X-ray fluorescence (XRF) methods. Reduction roasting of limonite was done at different temperatures (750°C, 850°C, 950°C, 1050°C) and coal as reducing agent (5%, 10%, and 15%) with a heating duration of 60 minutes. The microscopic and XRD analysis showed that limonite ore contains goethite, talc, quartz, lizardite, and maghemite. The chemical composition of limonite ore determined using XRF was dominated by Fe2O3 (56.74%) followed by SiO2 (19.70%), Al2O3 (6.43%), MgO (4.05%), Cr2O3 (1.59%), MnO (0.67%), and Ni (1.43%). Roasting of limonite at 750°C - 850°C has led to the transformation of goethite into hematite [Fe2O3], and maghemite [γFe2O4]. Further temperature raising at 950°C caused the formation of magnetite [Fe3O4], whereas talc and lizardite were altered to forsterite [Mg2SiO4]. At the temperature of 1050°C, the minerals such as fayalite [Fe2SiO4], spinel [MgAl2O4], and tridymite [SiO2] were formed. The result of the reduction roasting experiment indicated that Ni could be upgraded up to 1.90% from the initial value in the ore of 1.43%, which was achieved at the roasting temperature of 1050°C with an addition of 15% coal reductant.

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