NORTHWEST GEOLOGY: What good is Columbia River basalt? by Steve Reidel
When I started studying the Columbia River basalt over 30 years ago, I thought that other than
groundwater and graveling roads, there wouldn't be any commercial use for the basalt. I remember one
scientist at Washington State University in Pullman had investigated the basalt as a source for insulation
material. Rock is one of the best insulating materials available and most of the insulation that you can
buy in a home-improvement store is made from rock. It is usually made from a silica-rich rock such as
granite or sandstone that is melted and extruded into thin fibers that are woven to produce those mats
that you see at the store.
It turns out that basalt makes the best rock insulation material. However, the problem with basalt as an
insulating material is that it melts at a very high temperature – 1100 degrees Celsius (that is about 2000
degrees Fahrenheit). The rock that goes into common insulation melts at about 600 degrees Celsius. It
costs a lot more money to make basalt into insulation so that WSU professor's idea never became
economical.
There is another possible use for basalt that my colleagues and I have been exploring at the Pacific
Northwest National Laboratory for the past several years. This is to remove carbon dioxide, one of the
greenhouse gasses, from the stacks of coal or natural gas burning power plants and 'sequester' it in the
ground.
Carbon sequestration, as it is called, is receiving a lot of attention lately. The point of this process is to
remove carbon dioxide from the stacks and pump it underground rather than letting it escape into the
atmosphere. The US Department of Energy's National Energy Technology Laboratory (NETL) is funding
many studies across the United States to see if this technology can help reduce greenhouse gases in the
atmosphere.
Most of the NETL's efforts have been going into examining deep saline aquifers that are usually found in
rock like sandstone. The point is to get carbon dioxide out of sight. There, the carbon dioxide is
'sequestered' in water with the hope that it won't leak back to the surface. However, ask any hydrologist
and they'll point out that there is no such thing as a non-leaking aquifer. A California national laboratory
and the Texas geological survey (Bureau of Economic Geology) are doing a field test in such a rock along
the Gulf coast.
We're looking at basalt as part of this program because basalt has a property that none of the other rocks
have. If you're a mineral collector like the folks at the Lakeside Mineral and Gem Club, you already know
why. It is because we find minerals in the basalt that show us that the basalt chemically reacts with
carbon dioxide to form new minerals – calcite and siderite.
Calcite is calcium carbonate and siderite is iron carbonate. Both minerals are a direct result of the
reaction of the calcium or iron from the basalt with carbon dioxide from the atmosphere that is usually
dissolved in groundwater. The product of this reaction is a new solid. That is the unique ability of basalt;
it can turn a gas into a solid with a simple natural reaction. This means that the reaction can lock up
carbon dioxide in a mineral and the gas can't escape back into the environment.
One question is how long will the reaction take? If it takes too long, it may be able to escape anyway. If it
takes too short of a time, then the place that carbon dioxide is injected could seal up right away.
My colleague Todd Schaef has been carrying out experiments to see how long that reaction will take and
under what conditions the reactions occur. As it turns out he has found that it is not a fast reaction so it
won't seal the injection site but it is fast enough so that the gas can't escape back to the environment.
With the experimental work done by Todd Schaef and his colleagues showing positive results, the next
thing to do is a field demonstration. A field demonstration would consist of taking a borehole and injecting
the carbon dioxide into one of the deep basalt aquifers. Most of the basalt aquifers deeper than 2500
feet below the surface are so bad that they can not be used for drinking water or irrigation so these would
be excellent test zones.
Even if a field test shows carbon dioxide can be safely locked up as a mineral in basalt, other problems
remain to be solved. An economic technology to get the carbon dioxide off a power plant stack must be
developed. It may turn out that just like the WSU professor who had a better insulation using basalt, the
financial costs of sequestering carbon dioxide in basalt (or anywhere) may turn out to be just too
expensive.
Steve Reidel is a geologist with the Pacific Northwest National Laboratory and can be reached at
sp.reidel@pnl.gov. Visit the lab's webpage at www.pnl.gov.
Sample of Columbia River basalt that was reacted with carbon dioxide. Dark material is basalt; white
material is the mineral calcite (calcium carbonate).