Investigation of Nickel Product Structures Developed during the Gaseous Reduction of Solid Nickel Oxide
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NICKEL metal has been used for many purposes and applications because of its high melting point, its resistance to corrosion, and its catalytic properties.[1] The principal source of primary nickel metal at present is sulfide ore; however there is an increasing trend in the further use of laterite ores. Nickel hydroxides, nickel carbonate, and nickel oxide are produced industrially as intermediate products in nickel laterite processing. To obtain a high grade nickel metal from this intermediate product, effective and controlled reduction processes need to be carried out. The reduction of solid NiO by using hydrogen gas is one of the options. The ability to conduct the process at a rapid rate, generate final product with high purity, and avoid the emission of greenhouse gases, as would be produced by other reducing agents, are some of the positive features of the hydrogen reduction process.[2] The overall reduction reaction of solid NiO with hydrogen gas can be expressed as follows: NiOðsÞ þ H2 ðgÞ ! NiðsÞ þ H2 OðgÞ
½1
The level of residual oxygen in the nickel metal product depends on the effectiveness of the hydrogen reduction process in the final stages of nickel processing. Since NiO is a known carcinogen, new regulations limiting oxygen contents of nickel products have been introduced by the European Union.[3] Careful control and T. HIDAYAT, Postgraduate Research Student, E. JAK, Director, and P.C. HAYES, Xstrata Professor of Metallurgical Engineering, are with the Pyrometallurgy Research Centre, The University of Queensland, Brisbane, QLD 4072, Australia. M.A. RHAMDHANI, formerly Postdoctoral Research Fellow, with the Pyrometallurgy Research Centre, The University of Queensland, is Lecturer, the Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Melbourne, VIC 3122, Australia. Contact e-mail: [email protected] Manuscript submitted August 24, 2008. Article published online May 27, 2009. 462—VOLUME 40B, AUGUST 2009
further improvements are needed to ensure these new targets are achieved in industrial practice. Many experimental studies have been carried out to investigate the gaseous reduction of nickel oxide with hydrogen;[4–13] however, there are only a limited number of investigations providing the information on the product structures formed during the reduction process. The detailed investigation of the product microstructure is certainly important, since it is associated with the overall reduction rate and the residual NiO in the final reduction product, as demonstrated in recent publications by Rhamdhani et al.[14,15] To ensure continued safe production of nickel using this process, further fundamental studies on the product structures formed during the reduction process need to be carried out.
II.
EXPERIMENTAL TECHNIQUES
Details of the experimental technique have been described in a previous publication by the authors.[16] Dense nickel oxide sheets were prepared by oxidizing 10 9 10 mm pure nickel metal sheet with starting thickness of 0.5 mm (99.98 pct Ni, Sigma-Al
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