Researchers Develop New Method for Ocean Sequestration of Carbon Dioxide Through Accelerated Weathering of Volcanic Rocks
7 November 2007
Researchers from Harvard and Penn State have developed a new method to enhance removal of carbon dioxide from the atmosphere and place it in the Earth’s oceans for storage. The work is described in a paper in the journal Environmental Science and Technology.
The process is a manipulation of the natural weathering of volcanic silicate rocks. Unlike other proposed ocean sequestration processes, the new technology does not make the oceans more acid and may be beneficial to coral reefs.
The technology involves selectively removing acid from the ocean in a way that might enable us to turn back the clock on global warming. Essentially, our technology dramatically accelerates a cleaning process that Nature herself uses for greenhouse gas accumulation.—Kurt Zenz House, graduate student in Earth and planetary sciences, Harvard University.
In natural silicate weathering, carbon dioxide from the atmosphere dissolves in fresh water and forms weak carbonic acid. As the water percolates through the soil and rocks, the carbonic acid converts to a solution of alkaline carbonate salts. This water eventually flows into the ocean and increases its alkalinity. An alkaline ocean can hold dissolved carbon, while an acidic one will release the carbon back into the atmosphere. The more weathering, the more carbon is transferred to the ocean where some of it eventually becomes part of the sea bottom sediments.
The engineered weathering process swaps the weak carbonic acid with stronger hydrochloric acid and thus accelerates the pace to industrial rates. HCl is electrochemically removed from the ocean and neutralized through reaction with silicate rocks. The increase in ocean alkalinity resulting from the removal of HCl causes atmospheric CO2 to dissolve into the ocean where it will be stored primarily as HCO3- without further acidifying the ocean.
In the thermodynamic limit—and with the appropriate silicate rocks—the overall reaction is spontaneous. A range of efficiency scenarios indicates that the process should require 100–400 kJ of work per mol of CO2 captured and stored for relevant timescales. The process can be powered from stranded energy sources too remote to be useful for the direct needs of population centers.
According to House, this would allow removal of excess carbon dioxide from the atmosphere in a matter of decades rather than millennia.
Besides removing the greenhouse gas carbon dioxide from the atmosphere, this technique would counteract the continuing acidification of the oceans that threatens coral reefs and their biological communities. The technique is adaptable to operation in remote areas on geothermal or natural gas and is global rather than local. Unlike carbon dioxide scrubbers on power plants, the process can as easily remove naturally generated carbon dioxide as that produced from burning fossil fuel for power.
The researchers, Kurt House; Daniel P. Schrag, director, Harvard University Center for the Environment and professor of Earth and planetary sciences; Michael J. Aziz, the Gordon McKay professor of material sciences, all at Harvard University and Kurt House's brother, Christopher H. House, associate professor of geosciences, Penn State, caution that while they believe their scheme for reducing global warming is achievable, implementation would be ambitious, costly and would carry some environmental risks that require further study. The process would involve building dozens of facilities similar to large chlorine gas industrial plants, on volcanic rock coasts.
The Link Energy Foundation, Merck Fund of the New York Community Trust, US DOE and NASA supported this work.
Kurt Zenz House, Christopher H. House, Daniel P. Schrag, and Michael J. Aziz. “Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change”, Environ. Sci. Technol., ASAP Article, 10.1021/es0701816
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