Ore mineralogy of nickel laterites: controls on processing characteristics under simulated heap-leach conditions

The mineral phases in more than 50 Ni laterite ores were determined before and after the ores were acid-leached in columns for more than 120 days. The selected ore samples have wide variations in initial chemical and mineralogical compositions and other properties, and their behaviour during treatment, including the proportions of Ni and Co extracted, exhibit similar extreme variations. Ores contain up to 13 quantifiable phases, including iron, manganese and chromium oxides, carbonates, kaolinite, serpentine, talc, chlorite, smectite, albite, hornblende and quartz. The highest Ni and Co concentrations were in the Mn-oxide phases that comprised <10 wt% in all test ores. Ores with high Ni grades (1.4-2.1 wt%) contained mainly smectite or chlorite, with low abundances of goethite and a variety of poorly crystalline phases. High Ni extractions (88-96%) during leaching were achieved mainly from low-goethite ores, but goethite abundance was not the only factor that influenced Ni extraction. Examination of the elements substituted in goethite indicated that greater Ni extraction was achieved from ores in which the Fe was partly replaced by Ni or Co. The cobalt grade in ores was related to the abundance of Mn-oxide phases, but the percentage of Co extracted during leaching did not correlate strongly with the abundance of any particular mineral phases. Cobalt extractions of >80% were achieved for only 12% of the ores tested in this study. While mineralogy ultimately determines the acid consumption of an ore, the mineral matrix in this suite of Ni laterites was sufficiently complex to prevent a simple predictive estimate.