UBC Theses and Dissertations
Carbon mineralization in ultramafic mine tailings via CO₂ injection Wynands, Eric
As CO₂ emissions continue to rise, the threat posed by anthropogenic climate change grows. To combat this crisis, technologies are needed to capture and store CO₂. Carbon mineralization is one approach, which reacts cations with CO₂ to form stable carbonate minerals. Ultramafic mine tailings are one cation feedstock that could be used to advance this strategy at scale. CO₂ injection into the porous medium is required to accelerate the mineralization rates. Ultramafic mine tailings vary widely in their reactivity to CO₂. One important mineral, brucite, reacts rapidly with CO₂. Thermogravimetric analysis was used to identify and quantify brucite abundances. The developed method improved brucite detection limits and could quantify brucite when phases, which interfere with identification by X-ray diffraction, are present. Centimetre-scale injection experiments were conducted on well-graded tailings grain size distributions on serpentinite (brucite-rich) and kimberlite (brucite-poor) samples. Well-graded grain size distributions enabled the permeability to inject into the porous medium. Reactive fine-grained brucite released most of its Mg, while lizardite leached a minority of its Mg in the brucite-poor samples. 0.1 to 1 wt.% CO₂ was sequestered into major hydromagnesite and minor nesquehonite. Metre-scale experiments in kimberlite tailings increased the scale and designed methods to achieve mine-scale injection. Compaction testing evaluated the relationship between the dry density and moisture content of the tailings. 6-metre-long pipe experiments replicated the reactivity of the centimetre scale. Scalable pad experiments injected CO₂ through a perforated pipe into a layer of mixed coarse and fine tailings. Plume development throughout the pad led to homogeneous reactivity. Heterogeneity and low abundances of sequestered carbon made confirming the gas-phase mass balance on the injected CO₂ using total inorganic carbon difficult. A similar magnitude of carbon was sequestered in PK, as observed at the centimetre-scale, varying from 0.1 to 0.2 wt.% CO₂. Carbon mineralization in mine tailings via CO₂ injection has been shown to be effective in accelerating passive sequestration rates. This observed reactivity equates to a minor reduction in mine emissions at carbon-intensive mines while being enough capacity to make low-carbon mines carbon neutral.
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