Challenges with Characterizing and Processing Goethite-Rich Jamaican Bauxites

Low-temperatureLow temperature aluminaAlumina plants in Jamaica traditionally process hematiteHematite-rich ores with manageable concentrations of mineral impurities. As these ores become scarce, the new bauxiteBauxite mines have lower available aluminaAlumina, higher goethiteGoethite, and higher concentrations of phosphorus, chromium, and manganese contaminants. Since the minerals associated with some of the minor impurities have not been identified, this paper explores whether the contaminants accumulate in the coarse or fine bauxiteBauxite fractions. Samples of hematiteHematite-rich bauxiteBauxite from the traditional mining areas and also goethitic ores from the new mines were wet-sieved into three size fractionsSize fraction (+200, −200/+325, and −325 mesh). Each fraction was investigated using X-ray fluorescence (XRF)XRF and X-ray diffraction (XRD)XRD spectroscopies. Following digestion, their caustic soluble concentrations of phosphorus, chromium, and zinc were also determined. The traditional bauxitesBauxite had no correlation between size fractionSize fraction and the aluminaAlumina, ironIron, calcium, or phosphorus concentrations in the ore, however larger particles had slightly more manganese impurities. In contrast, larger particles from the new mines had higher concentrations of ironIron” and chromium impurities while smaller particles contained marginally more aluminaAlumina”. During digestion, the new bauxitesBauxite” gave higher caustic soluble P, Zn, and Cr and will be more challenging and costly to process into aluminaAlumina that meet the required specifications.