Effect of pressure, temperature, and aqueous carbon dioxide concentration on mineral weathering as applied to geologic storage of carbon dioxide

CO2 mediated dissolution of silicate minerals and subsequent precipitation of carbonates in deep saline aquifers may allow permanent trapping of carbon dioxide. However, the time-scales and extents of the reactions are poorly understood for CO2 receptor formation conditions. To address these shortcomings, experiments were conducted to investigate the effects of pressure, temperature, and aqueous solution composition on rates and mechanisms of silicate mineral dissolution and carbonate precipitation. A high pressure/high temperature flow-through reactor system was used to derive steady-state dissolution rates of crushed forsteritic olivine. The system allowed continuous monitoring of temperature, pressure, and pH, and periodic sampling of effluent fluids for dissolved ion concentration analysis. Preliminary measurements of dissolution rates indicate good agreement with previously published measurements at ambient conditions. Increasing the pressure from 1 to 100 bar under constant CO2 conditions increased the dissolution rate by similar to80%. The same reactions were studied in batch systems using an array of analytical techniques to investigate dissolution mechanisms and secondary precipitate formation. The extent of olivine dissolution in the batch reactors increased with temperature, P-CO2 and surface area. Precipitation of magnesium-rich carbonates on reacted olivine was observed at initial magnesite saturation indices greater than 1.6.