Nickel laterites part I: microstructure and phase characterisation during reduction roast and leaching processes

Detailed microstructure and phase characterisations of processed nickel laterite ore feed, reduced ore and leached ore have been carried out using scanning electron microscope, synchrotron X-ray powder diffraction and electron probe X-ray microanalysis as a part of study aimed to increase Ni recovery from the laterite ores. The majority of the nickel in the ore feed were found to be associated with fine grained goethite (Fe rich matrix of limonite composite) and serpentine particles. These phases were transformed to magnetite and olivine respectively upon reduction roasting. Nanosize metallic particles were also observed on the free surface of limonite composite particles following reduction roasting. Upon leaching, >90% of the nickel in the Fe rich matrix was leached out, while <50% was removed from the olivine and its composites. The characterisation results from this study were used to assist the analysis of thermodynamic and phase changes during reduction roasting and leaching described in Part 2 of the paper.