Acid resistance of goethite in nickel laterite ore from Western Australia. Part I. The relationship between goethite morphologies and acid leaching performance

• Limonitic laterites show varied leaching rates in atmospheric pressure leaching.
• The effect of morphology on leaching rates outweighs that of mineralogy.
• Goethite paragenetically interlaces with silica/kaolinite in slow leach laterites.
• Acicular goethite dominates in fast leach laterite ores.
• TEM imaging is effective in differentiating between fast and slow leach goethite.

Nickel containing goethite in laterite ores shows extreme variability in heap leaching performance. This has been difficult to characterise making utilisation of these ores for heap leaching problematic. The variability of the leaching performance is demonstrated for selected samples using atmospheric pressure leaching. Quantitative mineralogical analysis based on X-ray diffraction, crystallite morphology from transmission electron microscopy imaging and the chemical composition measured by energy dispersive X-ray spectrometry of the pre- and post-leached laterite ore samples suggests acid resistant (slow leaching) goethite is paragenetically interlaced with silica or kaolinite. Caustic digestion is shown to be effective in breaking up cementation frameworks and liberating the goethite interlaced by silica or kaolinite. Large single domain goethite and high chromium substituted goethite are also identified in the slow leaching samples. A better understanding of the microstructure of the acid resistant laterite ores is expected to lead to improvement in the hydrometallurgical processing for these ores.

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