SILICATE WEATHERING AT PRESSURE, TEMPERATURE, AND AQUEOUS CARBON DIOXIDE CONDITIONS RELEVANT TO GEOLOGIC CARBON SEQUESTRATION

Carbon dioxide storage in deep saline aquifers as part of a carbon mitigation strategy will alter aquifer geochemistry and affect water-rock interactions. While dissolution rates will increase following a decrease in pH, the release of base cations such as magnesium to solution may facilitate precipitation of carbonate minerals. Both dissolution and precipitation processes can affect the reservoir porosity and permeability. Although silicate weathering has been studied for many years, the time-scales and extents of associated reactions are poorly understood for receptor reservoir conditions.

Forsteritic olivine (Fo₉₀) reaction rates, mechanisms, and products are investigated in flow-through and batch laboratory experiments performed at pressure, temperature, and aqueous carbon dioxide conditions relevant to geologic carbon dioxide storage. Olivine is employed as a model mineral because of its congruent and rapid dissolution and potential for secondary precipitation of magnesium and iron(II) carbonates. The effects of pressure, pH, and carbon dioxide concentration on the dissolution rate are investigated using a flow-through reaction apparatus that was designed and constructed at Princeton University. Steady-state macroscopic dissolution rates are quantified by measuring concentrations of magnesium, iron, and silicon in the reactor effluent with inductively coupled plasma optical emission spectroscopy. In batch experiments, aqueous phase analysis is combined with solid phase characterization to identify potential reaction mechanisms and products. Weathered solids and secondary precipitates are characterized with an array of spectroscopic, electron microscopic, physical adsorption, and X-ray diffraction techniques. Complementary geochemical modeling simulations are used to interpret the effect of reaction affinity on the dissolution rate and the extent of supersaturation required for the precipitation of carbonates.