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Mechanical activation of ultramafic mine waste materials for enhanced mineral carbonation Li, Jiajie


The potential success of integrating mineral carbonation, as a pathway to CO₂ sequestration, in mining projects, is dependent on the mineralogical composition and characteristics of its waste rock and tailings. Ultramafic rocks have proven the best potential substrate for mineral carbonation and their ability to alter and to convert CO₂ into its carbonate mineral form is dependent on the original mineralogy and particle surface area. CO₂ conversion kinetics is complex and with the application of appropriate comminution technologies, its efficiency can be enhanced. The objective of this research is to evaluate mechanical activation to enhance the carbonation storage capacity of mine waste material. Three approaches were taken in this research. The first approach was to characterize the microstructure of the mechanically-activated mineral olivine, a predominant mineral constituent of ultramafic rocks, using X-ray diffraction patterns and line profile analysis methods with full pattern fitting method. The second approach was to compare the structural and chemical changes of mine waste with pure olivine, both of which were activated by various mechanical forces under both wet or dry conditions and subsequently carbonated in a direct aqueous carbonation process. Regardless of milling conditions, forsterite (Mg₂SiO₄), the olivine mineral variety in the mine waste, was found to be the main mineral being mechanically-activated and carbonated. It was determined that lizardite (Mg₃(Si₂O₅)(OH)₄), a hydrated magnesium silicate also common in ultramafic hosted mineral deposits, acted as catalyzer assisting forsterite reaching high levels of activation. This condition generated a greater CO₂ conversion to carbonate than that of pure olivine with the equal specific milling energy input. The stirred mill proved to be the most efficient form of mechanical activation vis-a-vis the direct aqueous carbonation process, followed by the planetary mill and the vibratory mill. The third approach analyzes the feasibility of mechanical activation in an integrated mineral carbonation process in a nickel mine considering the life cycle of the process. The minimum operating cost for 60% CO₂ sequestration efficiency was 105-107 $/t CO₂ avoided. At this point, the Turnagain project can potentially sequester 238 Mt/y CO₂ using its waste during the 28-year life of mine.

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