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    Will Permanent CO2 Sequestration Work? An Abandoned Mine May Hold The Key
    By News Staff | December 9th 2013 10:57 AM | 8 comments | Print | E-mail | Track Comments


     Red Mountain, an abandoned California magnesite mine, is providing geoscientists new insights on how to permanently entomb greenhouse gas emissions in the Earth.

    The Red Mountain mine is about 70 miles east of the campus and contains some of the world's largest veins of pure magnesium carbonate, or magnesite – a chalky mineral made of carbon dioxide (CO2) and magnesium. How the magnesite veins formed millions of years ago has long been a puzzle but the scientists have an idea for converting CO2, a potent greenhouse gas, into solid magnesite. 

    "Conventional geological storage involves capturing CO2 from industrial smokestacks and injecting it as a fluid into the subsurface," said Kate Maher, an assistant professor of geological and environmental sciences at Stanford. "But there is concern that the carbon dioxide would eventually leak back into the atmosphere. Our idea is to permanently lock up the CO2 by converting it into a stable mineral."

    Power plants and other industries are responsible for more than 60 percent of global CO2 emissions, according to the International Energy Agency . Sequestering the CO2 in magnesite deposits would prevent the gas from entering the atmosphere and warming the planet, Maher explained.



    Stanford University students study the geologic origins of magnesite deposits inside the abandoned Red Mountain mine east of campus. Credit: Pablo Garcia del Real, Stanford University


    Magnesite mining



    Magnesite was used in the early 20th century for iron smelting and manufacturing cement. The Red Mountain mine operated for about 50 years until the late 1940s.

    At Red Mountain, the Stanford team has identified more than 20 large veins of pure magnesite embedded in magnesium-rich ultramafic rock. The biggest vein is about 118 feet (36 meters) wide and 886 feet (270 meters) long. More than 50 percent of the magnesite in each vein consists of CO2, the rest is magnesium.

    Ultramafic rocks make up about 1 percent of the Earth's surface and occur near regions undergoing rapid population and industrial growth, Maher said. More than 50 other deposits of exceptionally high-grade magnesite are distributed in the California Coast Ranges alone. Sequestering CO2 emissions at these sites could play a significant role in curbing global warming, she added.

    "We've been looking at the geologic structure and veining at Red Mountain to try and understand how hard ultramafic rock could be transformed into magnesite," Maher said.

    The Stanford team estimates that Red Mountain originally held nearly 1 million metric tons of magnesite, of which about 83 percent has been mined.

    "One million metric tons of magnesite is the equivalent of sequestering 140,000 metric tons of carbon in mineral form," said graduate student Pablo Garcia del Real.

    "Our goal is to use the vast reservoirs of magnesium stored in ultramafic rocks to chemically bind with CO2 and form magnesite. But as we discovered at Red Mountain, breaking those rocks is one of the main engineering challenges that we face."


    San Andreas fault



    After several field trips to Red Mountain and a series of laboratory tests, Maher and her co-workers concluded that tectonic forces played a crucial role in creating the magnesite deposits.

    "To unlock the secrets of these deposits, we needed to find clues about both the mineralization process and the geologic history of the area," del Real said.

    California's infamous San Andreas fault lies less than 40 miles west of Red Mountain. The fault formed about 29 million years ago, creating a large gap between the Earth's crust and the hot mantle below. The gap allowed heat to rise to the surface, raising the temperature of the water and liquid CO2 trapped in the ultramafic rocks.

    "When the temperature of a liquid increases, the volume increases," del Real said. "We think that the CO2 enhanced the ability of the water to expand, adding enough pressure to break the ultramafic rock and cause the chemical reaction that formed the magnesite veins."

    The process was fast and furious, he added.

    "The magnesite veins are very white, homogenous and composed of very tiny crystals, so they probably formed quickly, perhaps instantaneously," del Real explained. "The ultramafic rocks appear shattered and broken, which means that this was a violent event."


    Low-temperature process



    Back at the lab, the Stanford scientists conducted an isotopic analysis of the magnesite samples collected at the mine. The results suggest that when the San Andreas fault opened, magnesite formed 1 kilometer below the surface as temperatures rose from about 53 degrees Fahrenheit (12 degrees Celsius) to 86 F (30 C). Such low temperatures should make it relatively easy for scientists to convert atmospheric CO2 into pure magnesite. But del Real and his colleagues have yet to replicate the process experimentally.

    "If we inject CO2 from a power plant or other point source into ultramafic rock, we would expect it to form magnesite," he said. "But when we try to make magnesite in the laboratory at low temperatures, it fails to form."

    For carbon sequestration to succeed, scientists will also have to figure out a way to make ultramafic rock permeable. "There is no way that CO2 or anything else will flow through these rocks," del Real said. He will discuss the problem of permeability at the AGU meeting on Dec. 10 at 10:20 a.m. PT in Moscone Center South, room 301.

    "In our research, we combine a big tectonics approach with the minute thermodynamic behavior of fluids," del Real said. "So we go from the very large scale to the very small scale."


    To be presented at the 2013 fall meeting of the American Geophysical Union (AGU) in San Francisco. Source: Stanford University

    Comments

    With vertical fractures and seismic events there are no guarantees they can reasonably contain contamimnates without leakage. Anytime subsurface geological pressure is augmented there are increased risks of man made earthquakes and related issues. Just because it's underground does not mean it is gone or that there will not be adverse impacts. The best way to reduce carbon emissions is simply to resort to cleaner energy solutions. It's more cost effective and far more manageable. The price point on schemes like this is too costly. Why build infrastructure to support an outdated dirty fuel technology when renewables are cleaner, safer and do-able?

    Hank
    Sure, but it's not known it won't work until the data is compiled to see if it will work. If our energy policy were rational, we would not have chased nuclear science and technology out of America 30 years ago.
    Why not take already bound carbon from the atmosphere, in the form of ultra-fast growing junk pines farmed by the paper industry, and dump the logs down into the various abandoned mines. I wouldn't expect there would be any worrisome contaminants leaching into the ground water, as it's all stuff that leaches into surface water any time one of those trees falls over and decays on the surface.

    Hank
    So sustainable, renewable wood is the problem? That's good to know. I was certain what environmentalists have been advocating for 50 years was a bad idea.
    No - it's part of the solution. Lots of parts to the solution, as it happens. The quick growing trees are good for carbon capture - they've been doing it a lot longer than we have, after all. The sustainable renewable hardwoods and such are good for construction and such.

    MikeCrow
    Well if you're going to grow lots of wood, why not use it for something purposeful, like houses or something? I bet we can build houses for the poor cheaper than extracting Co2 from the atmosphere.
    Never is a long time.
    It's a good thought, at first glance, but there's a couple of problems with it.

    1) Housing in general, and most construction for that matter, is not long-term storage - at least not geologically long term storage. Buildings get depreciated out over 30 years or so, and then are liable to be torn down and replaced. The construction waste ends up being chipped and burned, putting CO2 back in the air, or it gets dumped in landfills - and landfills are something we should be getting rid of. Now, if someone had a relatively cheap and effective means of using virtually all of a tree as a source stock for hydrocarbons and other petrochemical products, that would be totally awesome.

    2) Exacerbating the construction problems, the cultivars that I am mentioning here - that the Paper Industry uses, are not engineered for strength, but for long, relatively simply separated fibers. They're meant to grow *FAST* - a section of forest intended for paper may take only 10-15 years before its ready for harvest.

    Ultimately, in a mine, they'll stay for very extended lengths of time, slowly decaying, being petrified, and any CO2 released in the decay process, being denser than the surface atmosphere, will tend to pool in the mine, not being disturbed by winds for the most part, and dissolve into ground water to be carried away deeper.

    For construction purposes, you want stands of longer, slower-growing hardwoods from a well managed hardwood tree farm.