Sequestration of non-pure carbon dioxide streams in iron oxyhydroxide-containing saline repositories

Iron oxyhydroxide, goethite (α-FeOOH), was evaluated as a potential formation mineral reactant for trapping CO₂ in a mineral phase such as siderite (FeCO₃), when a mixture of CO₂-SO ₂ flue gas is injected into a saline aquifer. Two thermodynamic simulations were conducted, equilibrating a CO₂-SO₂ fluid mixture with a NaCl-brine and Fe-rich rocks at 150 °C and 300 bar. The modeling studies evaluated mineral and fluid composition at equilibrium and the influence of pH buffering in the system. Results show siderite precipitates both in the buffered and unbuffered system; however, the presence of an alkaline pH buffer enhances the stability of the carbonate. Based on the model, an experiment was designed to compare with thermodynamic predictions. A CO₂-SO₂ gas mixture was reacted in 150 ml of NaCl-NaOH brine containing 10 g of goethite at 150 °C and 300 bar for 24 days. Mineralogical and brine chemistry confirmed siderite as the predominant reaction product in the system. Seventy-six mg of CO₂ are sequestered in siderite per 10 g of goethite.