Reactivity of sandstones under conditions relevant to geosequestration: 1. Hematite-bearing sandstone exposed to supercritical carbon dioxide commingled with aqueous sulfite or sulfide solutions

Reactivity of a red sandstone under conditions relevant to geosequestration was studied experimentally. Crushed Moenkopi sandstone from the lower Triassic was exposed to supercritical CO2 containing commingled aqueous sulfite or sulfide solutions as proxies for SO2 or H2S co-injected along with CO2. Flow-through experiments simulating conditions near the point of injection and batch experiments simulating conditions at the water-side of the edge of the CO2 plume were conducted. Mِssbauer spectroscopy, X-ray diffraction, and Fourier transform infra-red spectroscopy were used to determine changes in iron mineralogy in both types of experiments. However, Mِssbauer spectroscopy, which solely derives its signal from the iron content in the sandstone, provides the most information on the changes in the iron mineralogy. The Moenkopi sandstone showed no change in iron mineralogy in any of the flow-through experiments. Pyrite was formed in batch experiments with supercritical CO2 and aqueous sulfide solutions, while siderite formed in batch experiments with super critical CO2 and an aqueous solution containing both sulfide and sulfite. The lack of reactivity in the flow-through experiments is probably due to the preferential wetting of mineral surfaces by the supercritical CO2 phase. In the batch experiments, the mineral surfaces are submerged in the aqueous phase throughout the experiment, which allows dissolved sulfur species to react with the minerals.