Mineralogical and Major Elemental Composition of Karst-Type Bauxite in the Bantimurung Area, Maros Regency of South Sulawesi Province, Indonesia

Abstract

As many as four karst-type bauxite samples from the Bantimurung area of Maros Regency, South Sulawesi, were studied to analyze their mineralogical and major-elemental compositions and to interpret their genesis and processing. Mineralogical characterization was conducted using optical microscopy, X-ray diffraction (XRD), and scanning electron microscope–energy dispersive spectrometry (SEM-EDS), whereas the major elemental composition was determined using X-ray fluorescence (XRF) spectrometry. Results of mineralogical analysis reveal that karst-type bauxite samples contain boehmite and minor gibbsite as the Al-bearing phases. The bauxite samples also comprise other minerals such as calcite, goethite, hematite, and quartz. The results of XRF analysis show that the average chemical composition of this karst-type bauxite consists of 34.04% Al2O3, followed by 18.88% SiO2, 13.85% Fe2O3, and 3.62% CaO. Karst-type bauxite also contains 1.49% TiO2, 27.79% moisture, and 1.93 Al2O3/SiO2. It is indicated that karst-type bauxite within the studied area is categorized as low-grade Al2O3 (<50%), and a lower Al2O3/SiO2 ratio (<10). The bauxite ore is likely formed as a result of the dissolution of silicate minerals overlying the limestone. Further dissolution of limestone leads to the formation of a sinkhole, as bauxite precipitation occurs there due to the immobility of Al and Fe. Based on the mineralogical and chemical composition, the ore can be upgraded using physical method such as washing, scrubbing, and magnetic method.