(720b) Kinetic and Mechanistic Studies of Chemical Enhancement of Carbon Mineralization

Carbon mineralization is one of the safest methods of sequestering anthropogenic carbon dioxide. It is based on the reaction of carbon dioxide with the metal ions present in silicate minerals to form geologically and thermodynamically stable mineral carbonates. Thus, this sequestration method allows virtually permanent carbon dioxide containment that does not require the long-term monitoring. Furthermore, the accounting and the certification of the stored carbon would be straightforward. For large scale carbon mineral sequestration processes, magnesium silicates, such as serpentine (Mg3Si2O5(OH)4) and olivine (Mg2SiO4), are the most suitable minerals due to their abundance in nature which far exceeds natural coal reserves. However, the reaction between minerals and carbon dioxide in nature is kinetically limited. This study focuses on the development of two-step (dissolution-carbonation) mineralization process based on the pH swing technology. The main objective of this study is to identify a mixture of chelating agents that can significantly enhance the mineral dissolution while also releasing metal ions during the subsequent carbonation step. First, a series of CO2-mineral-water systems is modeled thermodynamically using Visual MINTEQ software. Based on the thermodynamic studies, a differential bed reactor is used to carry out the kinetic studies of the chemically enhanced dissolution of serpentine using various chelating agents that target both Mg- and Si-rich layers of minerals. Unlike in a batch reactor, this reactor system can capture the fast reaction kinetics during the first few minutes of the dissolution process without the need of a buffer solution. The effects of pH, ionic strength and reaction temperature on the serpentine dissolution are investigated, while various chelating agents are evaluated as the chemical enhancer for the mineral dissolution. The reaction progress is also monitored via a series of XRD analyses of mineral specimens during experiments.