THE SELECTIVE SULPHIDATION AND PHYSICAL UPGRADING OF NICKEL FROM A NICKELIFEROUS LATERITIC ORE
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The processing of nickeliferous laterites to produce nickel metal is both complex and energy intensive. Since most laterites are found in remote regions, the capital costs for the infrastructure can exceed those for the process itself. The low temperature sulphidation of lateritic ores to produce an intermediate nickel concentrate for further processing offers a number of potential advantages, such as lower energy consumption and a relatively simple flowsheet. In this research, the sulphidation of a nickeliferous lateritic ore was investigated between the temperatures of 450-1100oC and sulphur additions of between 25-1000 kg of sulphur per tonne of ore. The experiments demonstrated that the nickel oxide within the ore can be selectively sulphidized to a nickel-iron sulphide. It was found that both the grade and the sulphidation degree largely depended upon the temperature and the sulphur additions, with temperatures above 550oC exhibiting the highest nickel sulphidation extents and grades. A DTA/TGA with mass spectrometer was used to further elucidate the nature of the phase transformations that occur upon heating of the ore, in the presence of sulphur. It was found that the Fe-Ni-S phase formed at low temperatures was submicron in nature and heating to temperatures of 1050oC-1100oC allowed for the growth of the sulphides to a d80 of up to 14 µm due to increased sulphide mobility, associated with the formation of a liquid sulphide matte with dissolved oxygen. Flotation studies conducted on 60 g samples showed that the sulphides formed respond to flotation with maximum grades of up to 6-7 wt% nickel being achieved and average grades of between 4-5 wt% nickel. Recoveries were approximately 50% on a sulphide basis and it was determined that the low nickel grades were due to the entrainment of magnetite fines.