Dynamics of passive minerals carbonation in ultramafic mining wastes and tailings
|Authors:||Entezari Zarandi, Ali|
|Advisor:||Larachi, Faïcal; Beaudoin, Georges; Plante, Benoît|
|Abstract:||Developing economically feasible strategies for long-term storage of carbon dioxide has become over the past few years a major stake in response to the concerns over global warming. Carbon capture and storage (CCS) is widely believed to be one of the possible scenarios aimed in challenging the global warming phenomenon by targeting the atmospheric CO₂ content. Mineral carbonation – in the platform of CCS – is anticipated to be a premium option for permanent carbon capture and storage owing to the known reactivity of alkaline materials such as magnesium silicates and brucite with carbon dioxide to form stable and environmentally benign carbonates. Passive mineral carbonation of ultramafic mine waste and tailing minerals could be considered as an economically attractive option owing the availability of large amounts of magnesium-rich mining wastes, which are regarded to be virtually free, typically fine grained and highly reactive. Moreover, the energy input of nature is employed in passive mineral carbonation which is likewise free. In this way, CO₂ is mainly dissolved in water resulting from rain and snow season. Metal ions such as Mg²⁺ and Ca⁺ are also leached into the water allowing the formation of metal bicarbonate and consequently formation of metal carbonates. Laboratory experimental works were done in order to identify the dynamics of passive mineral carbonation under environmental conditions prevailing the Quebec region, Canada. A differential diffusion carbonation cell was developed to monitor the kinetics of mineral carbonation under ambient conditions. The kinetic measurements revealed the complex role of water both as reacting medium and moiety in the carbonation pathway. Time-dependent X-ray powder diffraction analysis and scanning electron microscopy reveal formation of transitional, metastable porous, flaky magnesium carbonates which subsequently evolved into less porous nesquehonite layers, which are shown to be responsible for surface passivation despite availability of unreacted brucite. However, surface abrasion was shown to liberate previously carbonated NIMT particles resulting in further carbonation on freshly exposed surfaces. Temperature dependent carbonation tests were performed in the ranges of hot (35 ± 1 °C), laboratory (23 ± 2 °C), low (5 ± 1 °C), and freezing (-5 ± 2 °C) to mimic different seasonal conditions. Temperature had a notable effect on the carbonation kinetics and lowering temperature caused a reaction slowdown despite carbonation is thermodynamically defined as an exothermic reaction. Moreover, it was observed that drying and freeze/thaw cycles were at the origin of a thermomechanical “peel-off” effect which inflicted micro–fractures to the carbonate product layers enabling water and gas to engulf beneath and react with freshly unearthed Mg donor sites. FTIR spectroscopy analysis revealed that hydrated magnesium carbonates such as nesquehonite are being formed parallel to brucite dissolution during mineral carbonation of brucite-rich nickel mining tailings. However, it was observed that nesquehonite is not the ultimate hydrated magnesium carbonate product. Long–term monitoring over 2 years of an already carbonated material revealed that the initial nesquehonite has evolved into dypingite and hydromagnesite depending on age, wetting/drying history and the depth where initial carbonate has been formed. Nonetheless, nesquehonite could maintain its stability over prolonged times if not being subjected to wet/ humid environmental conditions.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||24 April 2018|
|Collection:||Thèses et mémoires|
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