Investigation of the reduction roasting of saprolite ores in the Caron process: microstructure evolution and phase transformations

ABSTRACT

Fundamental studies have been undertaken to determine the microstructural and phase transformations occurring during the reduction roasting of saprolite ores. Laboratory studies have been undertaken to simulate the conditions occurring during the reduction roast step of the Caron Process. Selected serpentine samples have been treated at temperatures between 500°C and 800°C in H₂/N₂ gas mixtures, and leaching tests on the reduced samples have been undertaken. Phase and microstructural changes have been characterised using X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) techniques.

A series of complex physical, microstructure and phase changes has been shown to occur during reduction roasting involving: (i) the dehydration of serpentine, (ii) the formation of a high-silica amorphous phase, (iii) the formation of Ni-Fe nanoparticles, and (iv) the nucleation, growth and recrystallisation of the forsterite (olivine) phase. The principal mechanism of removal of nickel from the reduced ore has been shown to occur through the selective leaching of the Ni-Fe alloy nano-particles from the surfaces in the product oxide.

KEYWORDS:

• Saprolite
• reduction roasting
• ferronickel alloy
• Caron process

Acknowledgements

The authors would like to acknowledge financial support for this research from the Australian Research Council Linkage program and our industry sponsor, QNI Yabulu, Townsville, Queensland, Australia. Particular thanks to John Fittock, QNI for his invaluable assistance in obtaining mineral samples for the research, and for providing valuable insight into the principles and industrial operation of the Caron process used at QNI. Thanks to the staff of The University of Queensland’s Centre for Microanalysis and Microscopy (CMM) for their support for sample analysis undertaken in the Centre. The authors also would like to acknowledge that some of the materials used in this manuscript have been previously published in COM2009 conference [8] and would like to thank Canadian Institute for Mining and Metallurgy (CIM) for allowing the use of these materials.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Australian Research Council Linkage [grant number LP0562201].