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A systematic investigation has been carried out to determine the effects of temperature, reduction/oxidation time, and partial pressure of hydrogen on the extent of the oxygen and sulfur removal during basic nickel carbonate (BNC) processing under laboratory conditions. It has been shown that increasing the temperature and reduction time increases the extent of oxygen and sulfur removal. Decreasing the hydrogen partial pressure tenfold lowers the extent of oxygen removal and results in the formation of residual NiO (incomplete reduction). The microstructure characteristics of industrial plant samples are correlated with the results obtained from the laboratory studies to identify the underlying elementary reactions and phenomena occurring and to understand the mechanisms of formation of the residual NiO in the final nickel product during industrial processing. As a result of these studies, it is recommended that the actual process is carried out at temperatures below 600 °C to avoid the formation of this residual NiO.
DOI: 10.1007/s11663-008-9139-5
© The Minerals, Metals & Materials Society and ASM International 2008
I. 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 high-quality 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 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.
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