216
Field experiments run a few years ago on basalts in Iceland investigated how
injected carbon dioxide would interact with the calcium-rich feldspars. The researchers were uncertain about how long calcite formation might take, but estimated the
mineral reactions might require decades if not centuries. Their focus was on methods to keep the carbon dioxide from migrating into the atmosphere during those
timeframes. Surprisingly, they discovered that substantial amounts of CO 2 inside
the basalt had transformed into calcite in just 2 years (Matter et al. 2016). Because
calcite is a solid mineral, concerns in other storage reservoirs about the potential for
trapped CO 2 to leak and migrate to the surface are not an issue in basalt. Over geologic time periods, the weathering of basalt has converted most of the dense carbon
dioxide atmosphere that the Earth originally possessed into calcite and limestones.
Limestone formations are especially prominent in the early Paleozoic, when levels
of CO 2 were higher.
There is no shortage of basalt deposits that could store CO 2 . These include the
Columbia River basalts in eastern Washington, Oregon, and southern Idaho, the
Deccan Traps in India, the bulk of the Hawaiian Islands, Japan, Iceland, the
Aleutians, and many other islands. The largest basalt volume of all resides in the
Mid-Ocean Ridge system, a gigantic, subsea mountain chain that encircles the
planet like the seams on a baseball. Other potential sources of calcium ions to turn
CO 2 into carbonate include seawater, and brines in sedimentary rocks like those
produced for salt in the nineteenth century by Samuel Kier and his contemporaries
in northern Pennsylvania.
Another, similar method using asbestos is under investigation. One of the minerals making up fibrous asbestos is chrysotile, a magnesium silicate. In theory, carbon
dioxide could react with the chrysotile to create magnesite, or magnesium carbonate. The fibrous nature of the asbestos minerals provides a very large surface area
for the reactions.
Direct air capture (DAC) can be done using natural methods like planting trees
or fertilizing the oceans to encourage plants to remove excess CO 2 from the atmosphere. However, when the plants die, the carbon has to be kept out of the atmosphere or there is no net GHG reduction. Burning the wood, for example, will just
put the carbon dioxide right back into the air. There are also issues with land availability and suitability for growing trillions of trees.
A second type of DAC is mechanical removal of CO 2 , using what are sometimes
called “artificial trees.” These employ either chemical or cryogenic methods to capture CO 2 from large volumes of air and store it underground away from the atmosphere. One advantage of the artificial tree systems is that they can be placed in
deserts, tundra, on high mountain peaks, and in other locations unsuitable for growing living trees (Kramer 2018).
Mechanical DAC has a substantial capital cost and requires large-scale machinery to process enough air volume to capture significant volumes of CO 2 . Systems
under design or in operation (one is currently operating in Switzerland) produce
CO 2 from air at costs ranging from about $100 to $600 per ton. Commercial CO 2
purchased from naturally occurring underground reservoirs costs $30 to $40 per ton
11 Balancing Energy, Environment, and Economics
Field experiments run a few years ago on basalts in Iceland investigated how
injected carbon dioxide would interact with the calcium-rich feldspars. The researchers were uncertain about how long calcite formation might take, but estimated the
mineral reactions might require decades if not centuries. Their focus was on methods to keep the carbon dioxide from migrating into the atmosphere during those
timeframes. Surprisingly, they discovered that substantial amounts of CO 2 inside
the basalt had transformed into calcite in just 2 years (Matter et al. 2016). Because
calcite is a solid mineral, concerns in other storage reservoirs about the potential for
trapped CO 2 to leak and migrate to the surface are not an issue in basalt. Over geologic time periods, the weathering of basalt has converted most of the dense carbon
dioxide atmosphere that the Earth originally possessed into calcite and limestones.
Limestone formations are especially prominent in the early Paleozoic, when levels
of CO 2 were higher.
There is no shortage of basalt deposits that could store CO 2 . These include the
Columbia River basalts in eastern Washington, Oregon, and southern Idaho, the
Deccan Traps in India, the bulk of the Hawaiian Islands, Japan, Iceland, the
Aleutians, and many other islands. The largest basalt volume of all resides in the
Mid-Ocean Ridge system, a gigantic, subsea mountain chain that encircles the
planet like the seams on a baseball. Other potential sources of calcium ions to turn
CO 2 into carbonate include seawater, and brines in sedimentary rocks like those
produced for salt in the nineteenth century by Samuel Kier and his contemporaries
in northern Pennsylvania.
Another, similar method using asbestos is under investigation. One of the minerals making up fibrous asbestos is chrysotile, a magnesium silicate. In theory, carbon
dioxide could react with the chrysotile to create magnesite, or magnesium carbonate. The fibrous nature of the asbestos minerals provides a very large surface area
for the reactions.
Direct air capture (DAC) can be done using natural methods like planting trees
or fertilizing the oceans to encourage plants to remove excess CO 2 from the atmosphere. However, when the plants die, the carbon has to be kept out of the atmosphere or there is no net GHG reduction. Burning the wood, for example, will just
put the carbon dioxide right back into the air. There are also issues with land availability and suitability for growing trillions of trees.
A second type of DAC is mechanical removal of CO 2 , using what are sometimes
called “artificial trees.” These employ either chemical or cryogenic methods to capture CO 2 from large volumes of air and store it underground away from the atmosphere. One advantage of the artificial tree systems is that they can be placed in
deserts, tundra, on high mountain peaks, and in other locations unsuitable for growing living trees (Kramer 2018).
Mechanical DAC has a substantial capital cost and requires large-scale machinery to process enough air volume to capture significant volumes of CO 2 . Systems
under design or in operation (one is currently operating in Switzerland) produce
CO 2 from air at costs ranging from about $100 to $600 per ton. Commercial CO 2
purchased from naturally occurring underground reservoirs costs $30 to $40 per ton
11 Balancing Energy, Environment, and Economics