CO2 mineralization of kimberlite residues from the Gahcho Kué Diamond Mine, Northwest Territories, Canada

Abstract

Kimberlite residues generated at diamond mines have the potential to substantially reduce net greenhouse gas emissions and contribute towards carbon-neutral mining. As part of the De Beers CarbonVault™, we conducted experiments using fine kimberlite residues from the Gahcho Kué Diamond Mine, Northwest Territories, Canada, to assess the mine's potential for CO₂ sequestration. Batch CO₂ leach tests indicate a CO₂ sequestration potential of 12 kg CO₂/t based on easily extractable cations from non-carbonate sources. However, an evaluation of the short-term reactivity of the residues post-deposition revealed the ability to sequester 0.86 kg CO₂/t when residues were allowed to dry through optimal water saturation (30–40 %). Furthermore, year-long weathering columns determined a CO₂ removal rate of 0.63 kg CO₂/t/yr, primarily through mineral trapping. Extrapolating these rates to current annual residue production and emissions indicates that 7 % of the mine's estimated CO₂e emissions could be sequestered over the life of mine. These rates are based on optimal storage conditions that keep residues exposed for long periods, which should be a consideration of residue management practices during the operating life of the mine and post closure. Further on-site investigations are necessary to refine rates and account for climatic conditions. Assessments conducted in this study affirm the suitability of Gahcho Kué residues for CO₂ sequestration and present strategies for optimizing this process.