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Posted: Apr 16, 2013

New tools reveal morphology, growth mechanisms of precipitates from supercritical CO2 storage

(Nanowerk News) Capturing carbon dioxide and storing it in underground rock formations is one proposed solution to mitigate climate change. New knowledge about the chemical reactions between CO2 and the mineral forsterite (Mg2SiO4) is helping determine how much confidence can be placed in using igneous rocks with magnesium-rich olivines as a solution for long-term CO2 sequestration.
To store CO2 waste, such as from industrial processing, it would need to be captured, condensed under high pressure and high temperature, and converted to supercritical CO2 (scCO2)—a fluid with both gas and liquid properties that could then be injected deep underground.
Researchers mimicked these deep underground conditions, incubating scCO2 in a highly humid environment with forsterite. They used imaging, including helium ion microscopy, as well as chemical analysis techniques at EMSL to study the changes in the chemistry of the system ex situ.
Critical to their studies, the research team developed a new sample preparation protocol to preserve the very fragile reaction products that formed under the high pressure and high temperature experimental conditions. A comparison of the results from synthetic, pure, porous forsterite and naturally occurring, impure, impervious forsterite, led the team to conclude that during incubation the magnesium carbonate mineral, hydrated dypingite [(Mg5(CO3)4•5H2O)], precipitates from solution—but via different growth mechanisms and with a different morphology for the different starting phases.
In synthetic forsterite, magnesium solutions seeped into pores where evaporation left rosettes of dypingite behind. On natural forsterite, dypingite precipitates formed only on the surface and in rod-like structures.
This finding ("Identification of Fragile Microscopic Structures during Mineral Transformations in Wet Supercritical CO2"), made possible by multimodal high-resolution imaging and spectroscopic analysis at EMSL, gives new insight into the geochemistry of scCO2storage. iffusion Studies (SEEDS) awards through the SunShot effort are Massachusetts Institute of Technology, Yale University, the National Renewable Energy Laboratory, The University of Texas at Austin, SRI International and Sandia National Laboratories.
Source: Environmental Molecular Sciences Laboratory
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