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Carbon sequestration in chrysotile mine tailings Wilson, Siobhan Alexandra

Abstract

Active sequestration of atmospheric carbon dioxide (CO₂) is occurring in chrysotile mine tailings at Clinton Creek, Yukon and Cassiar, British Columbia. Hydrated magnesium carbonate minerals develop in mine tailings as a natural consequence of the weathering process within the residues. Magnesium, leached from silicate minerals, reacts with dissolved CO₂ and bicarbonate in rainwater, precipitating carbonates at the surface of tailings upon evaporation of pore fluids and in near-surface environments with possible mediation by photosynthetic microbes. Increased reaction rates are observed in the tailings environment due to fine grain size resulting from mineral processing. Mine tailings may therefore represent the optimal environment in which to pursue mineral sequestration. Stable carbon and oxygen isotopes and radiogenic carbon are used to confirm an atmospheric source for CO₂ in recently-precipitated carbonate efflorescences in mine tailings. X-ray powder-diffraction studies demonstrate that CO₂ is crystallographically bound within the hydrated magnesium carbonate minerals nesquehonite [MgCO₃∙H₂O], dypingite [Mg₅(CO₃)₄(OH)₂∙5H₂O], hydromagnesite [Mg₅(CO₃)₄(OH)₂∙4H₂O], and lansfordite [MgCO₃∙5H₂O]. Quantitative phase analysis with the Rietveld method for X - ray powder-diffraction is used to determine the modal abundance of hydrated magnesium carbonates in mine tailings. Isotopic-fingerprinting and the Rietveld method are an effective verification protocol for carbon sequestration in mine tailings.

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