How I Helped Turn Carbon Dioxide into Stone

By Dom Wolff-Boenisch, Curtin University | June 9, 2016 5:15 pm

Iceland’s geothermal power plants are an ideal place to test pumping carbon dioxide underground. (Credit: Dom Wolff-Boenisch)

To halt climate change and prevent dangerous warming, we ultimately have to stop pumping greenhouse gases into the atmosphere. While the world is making slow progress on reducing emissions, there are more radical options, such as removing greenhouse gases from the atmosphere and storing them underground.

In a paper published today in Science my colleagues and I report on a successful trial converting carbon dioxide (CO₂) to rock and storing it underground in Iceland. Although we trialled only a small amount of CO₂, this method has enormous potential.

Here’s how it works.

Turning CO₂ to Rock

Our paper is the culmination of a decade of scientific field and laboratory work known as CarbFix in Iceland, working with a group of international scientists, among them Wallace Broecker who coined the expression “global warming” in the 1970s. We also worked with the Icelandic geothermal energy company Reykjavik Energy.

The idea itself to convert CO₂ into carbonate minerals, the basis of limestone, is not new. In fact, Earth itself has been using this conversion technique for aeons to control atmospheric CO₂ levels.

However, scientific opinion had it up to now that converting CO₂ from a gas to a solid (known as mineralization) would take thousands (or tens of thousands) of years, and would be too slow to be used on an industrial scale.

To settle this question, we prepared a field trial using Reykjavik Energy’s injection and monitoring wells. In 2012, after many years of preparation, we injected 248 tons of CO₂ in two separate phases into basalt rocks around 550m underground.

Most CO₂ sequestration projects inject and store “supercritical CO₂”, which is CO₂ gas that has been compressed under pressure to reduce considerably its density. However, supercritical CO₂ is buoyant, like a gas, and this approach has thus proved controversial due to the possibility of leaks from the storage reservoir upwards into groundwater and eventually back to the atmosphere.

In fact, some European countries such as the Netherlands have stopped their efforts to store supercritical CO₂ on land because of lack of public acceptance, driven by the fear of possible leaks in the unforeseeable future. Austria went even so far as to ban underground storage of carbon dioxide outright.

The injection well with monitoring station in the background. (Credit: Dom Wolff-Boenisch)

Our Icelandic trial worked in a different way. We first dissolved CO₂ in water to create sparkling water. This carbonated water has two advantages over supercritical CO₂ gas.

First, it is acidic, and attacks basalt which is prone to dissolve under acidic conditions.

Second, the CO₂ cannot escape because it is dissolved and will not rise to the surface. As long as it remains under pressure it will not rise to the surface (you can see the same effect when you crack open a soda can; only then is the dissolved CO₂ released back into the air).

Dissolving basalt means elements such as calcium, magnesium, and iron are released into pore water. Basaltic rocks are rich in these metals that team up with the dissolved CO₂ and form solid carbonate minerals.

Through observations and tracer studies at the monitoring well, we found that over 95 percent of the injected CO₂ (around 235 tonnes) was converted to carbonate minerals in less than two years. While the initial amount of injected CO₂ was small, the Icelandic field trial clearly shows that mineralization of CO₂ is feasible and more importantly, fast.

Storing CO₂ Under the Oceans

The good news is this technology need not be exclusive to Iceland. Mineralization of CO₂ requires basaltic or peridotitic rocks because these types of rocks are rich in the metals required to form carbonates and bind the CO2.

As it turns out the entire vast ocean floor is made up of kilometer-thick oceanic basaltic crust, as are large areas on the continental margins. There are also vast land areas covered with basalt (so-called igneous provinces) or peridotite (so-called “ophiolitic complexes”).

The overall potential storage capacity for CO₂ is much larger than the global CO₂ emissions of many centuries. The mineralization process removes the crucial problem of buoyancy and the need for permanent monitoring of the injected CO₂ to stop and remedy potential leakage to the surface, an issue that supercritical CO₂ injection sites will face for centuries or even millennia to come.

On the downside, CO₂ mineralization with carbonated water requires substantial amounts of water, meaning that this mineralization technique can only succeed where vast supplies of water are available.

However, there is no shortage of seawater on the ocean floor or continental margins. Rather, the costs involved present a major hurdle to this kind of permanent storage option, for the time being at least.

In the case of our trial, a tonne of mineralized CO₂ via carbonated water cost about US$17, roughly twice that of using supercritical CO₂ for storage.

It means that as long as there are no financial incentives such as a carbon tax or higher price on carbon emissions, there is no real driving force for carbon storage, irrespective of the technique we use.

The Conversation

This article was originally published on The Conversation. Read the original article.

CATEGORIZED UNDER: Environment, Top Posts
  • Uncle Al

    (∆P)(∆V) = energy, 101.325 J/liter-atm. Capturing, transporting, compressing, and injecting liquid or supercritical fluid carbon dioxide plus 25× by weight water “deep underground” consumes 30 – 40%% of the enthalpy of combustion of carbon to carbon dioxide. How fast must one run to win the Red Queen’s race?

    Ignore Oklahoma wherein deep injection of waste water from ordinary petroleum and fracking operations transformed that state into a tectonic shake table. “248 tons of CO2” A state-of-the-art, integrated gasification combined cycle coal power plant emits 726 tonnes of CO2/GW-hr. Congratulations! You net buried about 13 minutes of one optimized US midwest power plant’s net CO2 emission. For how long did the injection proceed? (248 tonnes/726 tonnes)(0.65 remaining after powering your prcoess)(60 minutes).

    there are no financial incentives” Add a 100% surcharge to the Carbon Tax on Everything.

    • OWilson

      No financial incentives?

      Give me enough “investment” (aka taxpayer gravy), and I can guarantee you will not be worrying about Co2, ever again :)

  • John C

    What would be the cost to taxpayers? Is there economy of scale?

    In Germany, the cost of their green drive was thrown onto the backs of taxpayers. Carbon intensive industries took advantage of loopholes to avoid paying their share.

    This technology sounds promising but am I going to be paying $8 a galkon for gasoline?

  • Gaz

    Really? All these comments instantly assuming they know better after reading one article about the concept. Stop being such naysayers and maybe acknowledge some great work. You cannot throw out an idea simply because the first version has limitations otherwise just about every tech we take for granted today wouldn’t exist. This is valuable what ever your egotistical reactions are.

    • Uncle Al

      Potemkin Klimate Kaos and its Carbon Tax on Everything are powerless against empirical observation – except to squeal. Go ahead, git, tell us how faith can break thermodynamics. I vote the straight ticket: 1) You cannot win (homogeneity of time plus Noether’s theorems); 2) You can only beak even on a very cold day (Carnot efficiency); 3) It never gets that cold (absolute zero is a singularity). “This is valuable” This post’s content is crap, even in the 19th Century.

      • Gaz

        Oh wow. Al, why don’t you reach out and contact these people to tell them that this process is not worth the effort? Maybe they forgot to run it past your graduate level physics first. Get a grip.

  • Darren Dickerson

    When the assets of the rich start falling into the sea money will be found to fix the problem.


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