Abstract
We present a tandem carbonation-assisted-flotation of nickel from low-grade ores, which conventionally faces challenges during nickel flotation due to its high process economics thereby deeming nickel unrecoverable on an industrial scale. Based on the fundamentals of CO2 sequestration in minerals, we explored the impact of carbonating a real low-grade untreated serpentine ore under extreme conditions and attained conversion of serpentine to magnesite at 22% and 16% in the presence and absence of inorganic salts, respectively. We then studied salt-free carbonation of untreated serpentine at moderate conditions of 70 °C, 1 MPa for 24 h and 1 h. Post-carbonation, we studied the carbonated particles using a scanning electron microscope, elemental mapping and energy dispersive X-ray spectroscopy and observed rhombohedral structures that suggested the formation of magnesium carbonate. We also found that Ni-Fe existed as sulfides which were confirmed as pentlandite through X-ray diffraction measurements. Finally, we performed Denver cell froth flotation experiments to test the real flotation behaviour of the carbonated and uncarbonated ores and found that carbonation in the presence of inorganic salts showed an improved nickel recovery of 7 wt.% than the uncarbonated ore and an improved nickel grade of 0.2 wt.%. This is the first study of its kind on extracting non-recoverable metals while sequestering CO2 successfully and will pave way for future research directions for combining mineral carbonation with the existing industrial processes.