Basic Nickel Carbonate: Part II. Microstructure Evolution during Industrial Nickel Production from Basic Nickel Carbonat
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INTRODUCTION
PROCESSES involving solid-gas reactions are widely used in metallurgical and materials production. An important application of the solid-gas reactions is in the production of nickel by thermal decomposition of basic nickel carbonate (BNC) and subsequent reduction of the decomposition product, nickel oxide.[1] The elementary reactions and fundamental phenomena occurring in the solid-gas reactions are complex, and they affect the microstructure evolution during processing and thus the final characteristics of the final nickel product. Understanding these phenomena is important for improved process control strategies to obtain highquality final nickel product, e.g., nickel with very low oxygen and sulfur contents. In the first article in this series,[2] a comprehensive literature review and fundamental studies of elemental reactions and phenomena taking place during oxidation and reduction processes in BNC processing were carried out. These studies are intended to provide information on the reactions occurring during industrial production of Ni metal. The modes of occurrences of the residual NiO in the final nickel product from the actual process were carefully investigated, and systematic investigations on the evolution of the phases, surface and internal
M.A. RHAMDHANI, formerly Postdoctoral Research Fellow, Pyrometallurgy Research Centre, The University of Queensland, Brisbane, QLD 4072, Australia, is Lecturer, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia. Contact e-mail: arhamdhani@swin. edu.au E. JAK, Associate Professor, and P.C. HAYES, Professor, are with the Pyrometallurgy Research Centre, The University of Queensland. Manuscript submitted October 18, 2007. Article published online April 12, 2008. 234—VOLUME 39B, APRIL 2008
microstructures of BNC, NiO, and nickel metal during controlled oxidation and reduction in laboratory were also carried out to identify the phenomena occurring during the processes. In the Section III of this paper, the effect of temperature, reduction time, and partial pressure of hydrogen on the extent of oxygen and sulfur removal during BNC processing in laboratory are discussed, extending the systematic investigations described previously. In the Section IV, the microstructure characterizations of industrial samples obtained from various locations along the production line of an industrial scale Ni production plant are presented; and these results are related to the results from the laboratory experiments to identify the actual fundamental phenomena taking place in industrial process and to propose the mechanisms by which the residual NiO microstructures are formed. Finally, the implications of the results for plant practice are described.
II.
EXPERIMENTAL
A. Materials For the laboratory study on the extent of oxygen and sulfur removal, BNC, supplied by BHP Billiton Yabulu refinery (Townsville, Australia), is used for the starting materials. The detailed characteristics of BNC particles used have been descri
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