Forsterite dissolution in saline water at elevated temperature and high CO2 pressure

Area of Science:

• Geochemistry
• Environmental Science
• Materials Science

Background:

• Magnesium silicate dissolution impacts aqueous chemistry and carbonate precipitation in geologic carbon sequestration (GCS).
• Understanding dissolution kinetics is vital for predicting CO2 fate and subsurface geochemistry during GCS.

Purpose of the Study:

• To investigate the effects of pressure, temperature, and salinity on forsterite dissolution rates under GCS-relevant conditions.
• To elucidate the mechanisms controlling magnesium silicate dissolution and its influence on GCS.

Main Methods:

• Batch experiments using forsterite (Mg(1.81)Fe(0.19)SiO(4)) powder.
• Varying CO2 pressure (10-100 bar), temperature (25-100 °C), and NaCl salinity (0-50,000 mg/L).
• Analysis of aqueous chemistry, reaction path modeling, and solid-phase characterization (SEM, XRD).

Main Results:

• Dissolution rate initially rapid, then declined due to silica-rich layer formation.
• Dissolution rate increased with temperature and CO2 pressure (via pH influence).
• NaCl enhanced dissolution, potentially by inhibiting silica layer formation.

Conclusions:

• Forsterite dissolution is controlled by surface layer formation and solution chemistry.
• Experimental data inform geochemical models for GCS performance assessment.
• Dissolution kinetics are critical for predicting CO2 behavior and subsurface evolution in GCS.