Reducibility of laterite ores
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I.
INTRODUCTION
T H E R E are two major types of nickel minerals, namely sulfides and oxides. The sulfide minerals, which are amenable to concentration, have been the principal source of metallic nickel. However, with the recent decline in sulfidic nickel reserves, the gamierites and laterites are becoming an increasingly important source of nickel, in spite of their low nickel grade and the fact that oxide ores cannot be upgraded by mineral processing techniques. Garnierite ores have been used primarily for producing ferro-nickel. Lateritic ores could be an attractive future raw material for the production of refined nickel, even though their nickel grades are low and iron assays high as compared to garnierite ores used in ferro-nickel production. Various methods have been developed for the recovery of nickel from lateritic ores. The Moa Bay Process and the Nicaro Process are a few examples of processes currently operated commercially. With the exception of a few entirely hydrometallurgical processes such as the Moa Bay Process, nickel oxide ores are generally selectively reduced at an early stage. Consequently, it is desirable to have an understanding of the reducibility of nickel oxide ores. In the present study, the reducibility was determined for several types of lateritic ores by means of a hydrogen reduction technique followed by a bromine-methanol leach for the determination of the degree of metallization. The fractions of nickel, cobalt, and iron reduced were determined individually from the leach solution with the objective of arriving at a relationship between reducibility and ore composition.
II.
EXPERIMENTAL METHOD
Table I shows the chemical compositions of five ore samples from the Dominican Republic used in this study. There M. KAWAHARA, formerly with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada, is Associate Professor, Department of Metallurgical Engineering, Kumamoto University, Kurokami, Kumamoto, Japan. J. M. TOGUR1, Professor, and R.A. BERGMAN, Adjunct Professor, are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, ON, Canada, M5S 1A4. Manuscript submitted February 12, 1987. METALLURGICALTRANSACTIONS B
are no significant differences among them with respect to the contained nickel and cobalt but large differences exist in the iron, magnesia, and silica content. Sample A is a serpentine type ore similar to gamierite ore, while B and E are limonites. The composition of sample C indicates that this ore lies between that of serpentine and limonite. Sample D is a mixture of the two ore types. The ores were dried ovemight at 393 K; they were then crushed and ground to - 2 0 0 mesh. Dry hydrogen gas was used as the reductant, and dry nitrogen gas for flushing. The flow rate of the hydrogen or nitrogen gas was maintained at 200 ml/min. A 500 mg sample of the desired ore was spread onto an alumina boat which was then heated in a horizontal furnace to the required temperature under a dry nitrogen atmosphere. Aft
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