As high grade nickel sulphide ores are being depleted and the challenges in economically processing nickel laterite ores continue, it appears that the future of nickel extraction lies with low grade ultramafic-hosted ores. Canada has been endowed with large resources from the low grade ultramafic nickel sulphide ores, particularly, in the Thompson nickel belt. Most of the deposits are large tonnage and open pittable but with low Ni grade and high MgO content. The common MgO-containing minerals are amphibole, olivine, chlorite, talc and serpentine. While chlorite and talc are floatable, they can be effectively depressed with carboxymethyl cellulose. The main challenge in processing the low grade ultramafic ores is serpentine which has three polymorphs: chrysotile, lizardite and antigorite. Chrysotile is the most common form of asbestos and this poses a serious health challenge in processing this type of ore due to the hazardous nature of the fibrous minerals. In addition, low grade ultramafic nickel ore may also contain brucite or hydrotalcite, which cause slurry viscosity to increase substantially and make grinding and flotation only possible at a very low solids percentage. This paper discusses the mineralogy and how it affects the recovery of nickel from low grade nickel sulphide ultramafic deposits in terms of grinding, flotation and rheological properties.
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