Alteration and carbonation of calcium and magnesium silicatesImplications on capture, storage and use of CO2

Résumé

The overall results of this experimental study for such different systems and process parameters (type of silicate phase(s), pH, T, pCO2, background electrolyte, dissolved inorganic carbons, DIC, carbon source) show that both natural Ca-Mg-Fe primary silicates, and aluminosilicate-rich industrial wastes (coal fly ash), can be safely and effectively used for CCS. Moreover, key parameters that control de dissolution-carbonation process resulting in secondary silicate phases formation, along with carbonates are identified. It is observed that mineral passivation can have a direct impact on silicate dissolution, hampering carbonation. Conversely, reaction-driven fracturing due to crystallization pressure exerted by secondary silicate phases is key for the successful progress of the carbonation reaction. However, it is also shown that formation of secondary silicates including divalent metals is a strong handicap for an effective mineral carbonation. But such detrimental effects could be by passed by selecting appropriate mineral feed and reaction parameters during ex situ mineral carbonation. Conversely, these experimental results show that enhanced mineral carbonation can be achieved during in situ GCS if pore waters include alkali metal ions that can favour the precipitation of secondary Na or K silicates. Finally, it is shown that zeolites along with carbonates are formed under hydrothermal condition during coal fly ash carbonation. This process is not only effective for CO2 mineral sequestration, but also results in the trapping and immobilization of potentially toxic elements such as heavy metals present in coal fly ash. Ultimately, these results show that mineral carbonation is not only and effective CCS strategy, but also have direct environmental applications for toxic element trapping, while at the same time resulting in the production of valuable minerals such as zeolites and calcite, with numerous industrial and technical uses. The latter ensures that recycling of alkaline industrial wastes is an economic and effective way to deal with the increasing problem associated with anthropogenic CO2 emission to the atmosphere.