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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.
"In the engineered weathering process we have found a way to swap the
weak carbonic acid with a much stronger one (hydrochloric acid) and
thus accelerate the pace to industrial rates," says House.
The researchers minimize the potential for environmental problems by
combining the acid removal with silicate rock weathering mimicking the
natural process. The more alkaline ocean can store carbon as
bicarbonate, the most plentiful and innocuous form of carbon in the
oceans.
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.
"This work shows how we can remove carbon dioxide on relevant
timescales, but more work is be needed to bring down the cost and
minimize other environmental effects," says Christopher H. House.
The Link Energy Foundation, Merck Fund of the
New York Community Trust, U.S. DOE and NASA supported this work.
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