A two-stage thermal upgrading process for nickeliferous limonitic laterite ores

Sulphide ore deposits are becoming increasingly less viable as a source of nickel, driving recent interest in the development of nickel laterite deposits. The difficulties with the current methods of nickel metal production from these oxide ores arise mainly from the inability to produce a concentrate analogous to that obtained in the flotation of sulphide ores, resulting in high production costs. In this work, a two-stage reduction and thermal growth process is proposed for the treatment of the nickeliferous limonitic laterite ores to produce a ferronickel product, recoverable by magnetic separation. An initial reduction roast of the ore with 6% coal and 4% sulphur additions at 600 degrees C for 1 h, followed by particle growth for 1 h at 1000 degrees C, produced a ferronickel concentrate with a nickel grade of 4% and a nickel recovery of 93.2%. The impact of particle growth temperature and retention time at temperature on the ferronickel particle size was also studied. For the control conditions, typical ferronickel particles produced were 10-20 mm in size. The particle size did not significantly change at temperatures higher than 1200 degrees C or for retention times beyond 60 min.