KINETICS OF OLIVINE CARBONATION AT 60oC AND 100 BAR

The climatic effects associated with increasing emissions of carbon dioxide (CO₂) from various point sources, such as coal-fired power plants, necessitate the development of methods to sequester CO₂ over geological time periods. One potential method is mineral carbonation, specifically the thermodynamically favored reaction of CO₂ with Mg-silicate minerals to produce Mg-carbonate minerals. Large, near-surface deposits of Mg-silicates are relatively abundant in the US and other parts of the world. Despite a considerable number of experimental studies addressing olivine ((Fe,Mg)₂SiO₄) dissolution kinetics, relatively few experiments have been carried out under conditions relevant to CO₂ sequestration. The present study seeks to examine the kinetic behavior of the dissolution of Mg-rich olivine and subsequent precipitation of magnesite (MgCO₃) in a unique batch reactor at 60°C and 100 bar, both with and without 1g/L salicylic acid solution. The reaction occurs inside a flexible, gold bag that is secured within a rotating autoclave. Liquid and gas samples are withdrawn throughout the experiment in order to monitor reaction progress without altering the pressure inside the reaction vessel. Liquid samples are analyzed for cation concentration, alkalinity, and carbon content; solids are analyzed following completion of the run, and reactions are modeled using CrunchFlow. Initial results show incongruent dissolution for the first 20-30 hours of reaction, followed by congruent dissolution in agreement with some previous experimental studies. Amorphous silica reaches thermodynamic saturation quickly, resulting in a layer on the olivine grains on the order of 100 nm thick. Despite this coating, quantitative XRD analysis revealed that 10% of the initial olivine was converted to magnesite over the duration of the experiments (44 days). The addition of 1g/L salicylic acid accelerated the rate of cation release into solution. In future studies, serpentinite will replace olivine as the feedstock material in order to investigate the carbonation kinetics of the more chemically complicated (and abundant) rock.