This Is CDR is an ongoing series of online events to explore the range of carbon dioxide removal solutions that are currently in development. And in most past episodes, we’ve talked about ways to capture carbon from the air. But once we’ve captured the tons, megatons, and eventually gigatons of carbon dioxide we’ll need to by the middle of the century, what do we do with it? One answer is, we store it safely and permanently in underground rock. For a look at emerging ways to do that, we’re joined this week by Dr. Peter Kelemen of Columbia University’s Lamont Doherty Earth Observatory, who researches mineralization pathways for CDR.
Dr. Kelemen’s research focuses on reactions between fluids and rocks. Certain silicate minerals, particularly peridotite, are perpetually reacting to ambient carbon dioxide in the air, turning it into solid carbonate rock. This is a natural process you can see in peridotite, with “fracture networks” of carbonized rock working their way into the larger silicate. (They’re called “ladder cracks” or “Frankenstein cracks” because they look like stitches.)
But the process as it occurs in nature is very slow. So Dr. Kelemen is experimenting with pumping carbon-saturated water through seams in peridotite. If the fluid is pumped at the right speed, the reaction generates just enough heat to be self-perpetuating. Dr. Kelemen estimates that with this technique, mineralizing and permanently sequestering a ton of carbon could cost as little as $10 to $20. (Which is good, because we’re going to have to sequester a lot of tons of carbon.)
Interestingly, a side-effect of the process might solve one of its own potential problems. As the reactive surface of the peridotite gets coated with newly solidified carbonate, it becomes less reactive; the reaction slows down. But at the same time, the growing volume of the injected carbon causes the peridotite to expand and then fracture further, exposing fresh surfaces to the carbon-saturated fluid. (Note that this is not the same as oil and gas fracking and does not create the same earthquake risk. (As Dr. Kelemen explains, the earthquake risk from oil and gas fracking is not from rock fragmentation itself but from injecting massive amounts of wastewater underground.)
As far as specific next steps, since Dr. Kelemen’s process requires peridotite and abundant water, the best location would be a coastal peridotite deposit. Luckily, these can be found in a number of places, including Hawaii, New Caledonia, and several parts of the Arabian Peninsula. Nothing is guaranteed, but Dr. Kelemen notes that small-scale experiments can tell us a lot. (For example, in an experiment using carbon “tagged” with sulfur hexaflouride, the carbon sequestration startup CarbFix was able to demonstrate that their own mineralization process had successfully solidified 93% of the CO2 they started with.)
We’re excited to hear more about Dr. Kelemen’s research as it progresses! After you check out his presentation above, you can read more about his work in this excellent Columbia Magazine profile from 2013. (Dr. Kelemen talks at the end about the difficulty in finding funding, and speculates that the world might be more ready in a decade or so–which puts us right on time!) Lastly, be sure to come back next week for more This Is CDR. You can also catch up on the whole This Is CDR series on our resources page.