Monday, June 13, 2016

Scientists Capture and Fix Carbon in Rock

In a paper released Thursday a team of scientists fromLamont-Doherty Earth Observatory at Columbia University, Institute of Earth Sciences at the University of Iceland, Department of Ocean and Earth Sciences at the University of Southampton , and Reykjavik Energy confirm the success and rapid storage of captured carbon dioxide as carbonate minerals in basaltic rocks. The scientists found that 95% of the CO2 injected at their CarbFix site in Iceland was mineralized to carbonate minerals within the rock in less than two years, much sooner than the scientists had originally predicted.

The capture and storage of carbon dioxide and other greenhouse gases in deep geologic formations has been part of every proposed plan to reduce greenhouse gases in our atmosphere. Carbon capture is really three activities: Gathering or capturing of CO2 from point sources (power plants, industrial plants, and refineries), transporting the captured CO2 to a geological storage site, and injecting the CO2 into the ground for permanent storage.

Until now, achieving permanent storage has been just a dream. CarbFix is a pilot project that has been running in Iceland since 2012. The project was created to test and optimize in situ mineral carbonation in basalt. The pilot consists of a CO2 pilot gas separation plant, CO2 injection pilot test, laboratory-based experiments, confirmation testing and numerical modeling.

The project was designed to inject 2.200 tons of CO2  and CO2 mixed with H2S per year in Iceland to test the feasibility of in situ mineral carbonation in basaltic rocks in the real world. The test site is at the Hellisheidi power plant in the southwest portion of Iceland. The Hellisheidi power plant is the world’s largest geothermal facility; it and a companion plant provide the energy for Iceland’s capital, Reykjavik, plus power for industry, by pumping up volcanically heated water to run turbines. While the process produces only about 5% of the CO2 of a coal fired plant, the process is not completely clean; it also brings up volcanic gases, including carbon dioxide and hydrogen sulfide (H2S).

The rocks in the area are basalt rocks which contain up to 25% by weight of calcium, magnesium, and iron. Basaltic rocks are highly reactive and are common covering  about 10% of continental surface area and most of the ocean floor.  The potential for carbonization is limited in sedimentary rock due to the lack of calcium-, magnesium-, and iron-rich silicate minerals required to form carbonate minerals .

The fate of the injected CO2 was monitored using isotopic tracers and chemical dyes. The injected CO2 was spiked with carbon-14 to monitor its transport and reactivity and the dyes were used to follow the water solution. The CO2 and CO2/H2S mixture, together with Carbon-14 tracers  were injected into the target formation fully dissolved in water pumped from a nearby groundwater well and then mixed with dyes. Typical injection ratio was  25-42  pounds of water for each pound of CO2 or CO2 and H2S.

The results of this study demonstrate that nearly complete in situ CO2 mineralization in basaltic rocks can occur in about 550 days. While the dyes were found downstream, the CO2 and Carbon -14 mixture was gone.

Scientists can now capture and permanently fix CO2.  Once stored within carbonate minerals the CO2 is fixed and stable, the risk of leakage is eliminated and any monitoring program of the storage site can be significantly reduced or eliminated entirely. The scaling up of this basaltic carbon storage method requires both massive quantities of water and porous basaltic rocks.  However, there are places where both are widely available . Typically this would be on the continental margins, such as off the coast of the Pacific Northwest of the United States.

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