Effect of Process Variables on Ni Extraction from Ultramafic Ores in the Thermal Treatment Method

The traditional high-grade sulfide mineral reserves are depleting, shifting the research focus towards ultramaficUltramafic resources since they are available in copious amounts and could meet the growing nickelNickel (Ni) demandDemand. Even though ultramaficUltramafic ores were discovered in the early 1920s, they have remained a resource due to the unavailability of economically viable methods for upgrading them. The ultramaficUltramafic ores are characterized by low-grade (0.4–0.8 wt.% Ni) and asbestos materials, posing safety, health, and environmentalEnvironmental risks. Moreover, their high MgO has detrimental effects on subsequent processes. The MgO affects flotationFlotation by slime coating, leachingLeaching by consuming a portion of the acidAcid, and smeltingSmelting by forming a viscous slagSlag, negatively affecting furnace integrity. In this work, our research group investigates a promising thermal upgradingThermal upgrading method for ultramafic concentratesUltramafic concentrate, which involves the addition of an iron (Fe) source to the concentrate, followed by heating the mixture to approximately 920 °C. During this heating process, the added Fe reacts with sulfur (S) to form nonmagnetic FeS, while Fe and nickelNickel (Ni) form magnetic FeNi. The key benefits of the process are the use of lower operating temperatures compared to conventional methods and a product suitable for subsequent physical separation based on magnetism differences. Our initial findings suggest that higher temperatures promote the formation of large FeNi particles, which enhance subsequent magnetic recovery. Although we have conducted extensive experimental investigations on the FeNi growth mechanism as a function of temperature in our previous work, further experiments are necessary to correlate Ni extractionNi extraction with FeNi growth to strike a balance between high Ni extractionNi extraction and magnetic recovery.