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Abstract:There is considerable interest in the development of new processes to extract the nickel from the oxidic nickeliferous laterite deposits, as the global nickel sulphide resources are rapidly becoming more difficult to access. In comparison to sulphide ores, where the nickel-containing mineral can be readily concentrated by flotation, nickel laterites are not amenable to significant upgrading, due to their complex mineralogy. In this paper, firstly, a brief overview of the conventional techniques used to process the nickeliferous limonitic laterites is given, as well as a review of current research in the area. Secondly, a thermodynamic model is developed to simulate the roasting process and to aid in the selection of process parameters to maximize the nickel recovery and grade and also to minimize the magnetite content of the concentrate. Thirdly, a two-stage process involving reduction roasting and thermal growth in either a tube furnace or a rotary kiln furnace, followed by magnetic separation, was investigated. Thermogravimetric, differential thermal and mineral liberation analyses techniques were utilized to further understand the process. Finally, the nickel grades and recovery results were compared to those available in the literature.

An increasing amount of nickel is currently being extracted from the nickeliferous laterite ores, rather than from the sulfide deposits. Consequently, new processes are being developed to extract the nickel from these ores and selective reduction is one possibility. In these processes, it has been shown that the addition of sulfur can improve the grade and/or the recovery. In the current work, the mechanism of the carbothermic reduction of a sulfurcontaining nickeliferous limonitic laterite ore was investigated by utilising TGA/DTA and both thermodynamic and kinetic analyses. It was found that, in addition to dehydroxylation and reduction, the reaction sequence also consisted of the following major stages: (1) conversion of pyrite to pyrrohtite and (2) subsequent desulfurisation. Analyses of the reacted samples showed that both the particle size and the amount of ferronickel increased with both particle growth temperature and retention time at temperature. The thermodynamic predictions were in general agreement with the experimental findings and were consistent with the postulated formation of an iron-sulfur-oxygen solution.

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