It has been a good year for mineral carbon dioxide sequestration.  The idea, first developed by Columbia Professor Klaus Lackner and others at Los Alamos National Laboratories in the mid-90s, is that one could keep CO2 gas out of the atmosphere and oceans by reacting it with magnesium or calcium silicate minerals to form stable carbonate minerals, such as magnesium or calcium carbonate.  Because carbonate minerals are the thermodynamic ground state of carbon at the Earth's crust, this process does not require energy to occur, and in fact as the recent article in OnEarth discusses, is happening naturally on large scales in areas where there are rocks with high concentrations of magnesium silicate minerals. 

Although this process happens naturally, the rates at which they take place in nature are generally too slow to balance the rate of CO2 emissions from our industrial processes. Thus scientists over the last 10 years have explored numerous routes through which to speed up these natural processes without consuming energy. The latest suggestion, coming from Columbia's Peter Kelemen and Juerg Matter discussed in this edition of onearth and originally published in the Proceedings of the National Academy of Sciences, makes light of observations showing that natural carbonation reactions can happen much more quickly than previously thought, if the conditions are right.  Now experimental data is trickling in showing that artificially creating those conditions through the injection of CO2 into the rocks may very well be possible.  This combined with the recent study published by my work group at Columbia (I recently finished my Ph.D under Prof. Klaus Lackner) in collaboration with the U.S. Geological Survey showing the abundance of appropriate rock formations in the United States is breathing new life into the idea of mineralizing CO2 as a potent greenhouse gas mitigation technology.

Map showing the distribution of magnesium silicate rocks suitable for use in a carbon mineralization process (USGS). 

The advantages of CO2 mineralization, especially when compared with other forms of carbon sequestration are enormous: The technology provides the potential for the permanent removal of CO2 from the environment through the production of an environmentally benign solid that is easy to monitor and verify.  In addition, the abundance of useful rock formations means that the capacity for CO2 storage is virtually unlimited. 

Beyond the idea of injecting CO2 into the rocks, several groups around the world are developing processes whereby the magnesium silicate minerals are mined, ground, and reacted with CO2 under optimized conditions in a reactor.  Initial development of these processes at the National Energy Techology Laboratory in the late 1990's demonstrated that the carbonation reactions can be made to happen in less than 30 minutes, fast enough to function as a mitigation technology.  So far that has only happened at the expense of large amounts of energy consumption, untenable for a CO2 sequestration technology.  Interestingly enough, only very little energy is consumed in the actual mining and grinding of the rocks, relative to the CO2 sequestered. It is the energy that has been consumed in the techniques used to speed up the carbonation reactions (such as pulverizing the rocks to particles smaller then dust, blasting the rocks with heat to destabilize their mineral structure, or using strong acids to digest the silicate minerals) that is as of yet prohibitive. 

At Columbia, Klaus Lackner's original idea for mineralizing carbon, combined with Juerg Matter's involvement in CO2 injection projects around the world and Peter Kelemen's expertise in ultramafic geology has created a hotbed for mineral sequestration research. Research is being pursued in both the area of injection into rock formations as well as identifying catalysts to enhance ex-situ reaction kinetics without consuming energy.  As mentioned, a handful of other universities around the world have researchers working on the issue, including the ETH Zurich, the Helsinki University of Technology, and the Abo Akademi University in Finland, and the Cato Institute and the University of Delft in the Netherlands.  Hopefully, we'll get to report back with some major developments in the near future.

[Image: Magnesium silicates (green) in Oman naturally absorb CO2 to form magnesium carbonate (white) (Sam Krevor).]