Thermal pre-treatment of refractory limonite ores to enhance the extraction of nickel and cobalt under heap leaching conditions

A low grade Western Australian slow-leaching limonite ore (Ore G) was selected to investigate the effect of thermal pre-treatment (roasting) upon the extraction kinetics of nickel and cobalt. The optimised thermal treatment conditions were established using batch roasting and bottle roll leaching tests to determine the effectiveness of each treatment relative to the leach performance of the untreated Ore G. The optimum treatment conditions were then applied to Ore G on a larger scale to provide a bulk sample for subsequent column leach tests. The faster leaching kinetics of both nickel and cobalt of the roasted ore were believed to be partially due to extra surface area created through water escape from goethite during the dehydroxylation process. Interestingly, however, the roasted ore consumes essentially the same amount of acid compared to untreated ore per unit of nickel extracted. Thus roasting of selected ores prior to heap leaching is a pre-treatment that could be applied to the vast WA resource of refractory goethitic ores which are currently not economic to process. The economics, however, would need to be assessed on a case by case basis with the additional processing costs needing to be at least off-set by the value of the recovered value metals.