Experimental and simulation studies of iron oxides for geochemical fixation of CO2-SO2 gas mixtures

Iron-bearing minerals are reactive phases of the subsurface environment and could potentially trap CO₂–SO₂gas mixtures derived from fossil fuel combustion processes by their conversion to siderite (FeCO₃) and dissolved sulfate. Changes in fluid and mineral compositions resulting from reactions, involving the co-injection of SO₂ with CO₂ were observed both theoretically and experimentally. Experiments were conducted with a natural hematite (α-Fe₂O₃) sample. A high pressure-high temperature apparatus was used to simulate conditions in geologic formations deeper than 800 m, where CO₂ is in the supercritical state. Solid samples were allowed to react with a NaCl–NaOH brine and SO₂-bearing CO₂-dominated gas mixtures. The predicted equilibrium mineral assemblage at 100 °C and 250 bar became hematite, dawsonite (NaAl(OH)₂CO₃), siderite (FeCO₃) and quartz (SiO₂). Experimentally, siderite and dawsonite, derived from the presence of kaolinite (Al₂Si₂O₅(OH)₄) in the parent material, were present in residual solids at longer reaction time intervals, which agreed well with results from the modelling work.