Can Sea Urchins Show Scientists How To Capture Carbon Affordably?

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"Can Sea Urchins Show Scientists How To Capture Carbon Affordably?"

According to a story in Gizmag yesterday, a group of researchers at Newcastle University in the U.K. may have accidentally stumbled on a solution to the problems that have bedeviled carbon capture and sequestration — by studying sea urchins.

“We had set out to understand in detail the carbonic acid reaction, which is what happens when CO2 reacts with water, and needed a catalyst to speed up the process,” Dr. Lidija Šiller, the leader of the team, said in a press release. “At the same time, I was looking at how organisms absorb CO2 into their skeletons and in particular the sea urchin which converts the CO2 to calcium carbonate.”

The use of calcium carbonate to grow shells and other bony parts is a trait urchins share with other marine animals. And when the team examined the urchin larvae, they found a high concentrations of nickel on their exoskeleton. Working off that discovery, they added nickel nanoparticles to their carbonic acid test. The result was the complete removal of the CO2 as it was converted into calcium carbonate.

According to Gaurav Bhaduri, a PhD student in Newcastle University and the lead author of the team’s paper, the methodology they derived — and have now patented — is simpler and much cheaper than the traditional enzyme-based approaches:

“The beauty of a Nickel catalyst is that it carries on working regardless of the pH and because of its magnetic properties it can be re-captured and re-used time and time again. It’s also very cheap – 1,000 times cheaper than the enzyme. And the by-product – the carbonate – is useful and not damaging to the environment.”

The research team developed a process to capture CO2 from waste gas by passing it directly from a chimney top through a water column rich in nickel nanoparticles. The solid calcium carbonate can then be recovered at the bottom of the column.

The researchers say their discovery could provide big CO2 emitters, such as power stations and chemical processing plants, with a cheap way to capture and store their waste CO2 before it is released into the atmosphere.

Every method invented so far to capture or sequester carbon from emitters before it can enter the atmosphere has suffered from difficulties regarding cost, feasibility, and side-effects. Pumping CO2 into the ground, for instance, is difficult, expensive, and carries risks of leakage, water contamination, and even earthquakes. Other processes, like the ones mentioned by Bhaduri, also convert CO2 into calcium carbonate or magnesium carbonate through the use of enzymes like carbonic anhydrase. But because of the chemical complexities they’re inefficient and expensive.

Calcium carbonate, which is essentially chalk, is widely used in the building industry to make cement and other materials. It’s even used by hospitals to make plaster casts. So once removed from the Newcastle team’s carbon capture process, the calcium carbonate could potentially be put to other uses.

The discovery certainly isn’t a cure all. The process can’t be fitted to car, so its use is limited to power plants and other major emitters. But Dr. Šiller believes it could someday have a big impact: “It is an effective, cheap solution that could be available world-wide to some of our most polluting industries and have a significant impact on the reduction of atmospheric CO2.”

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47 Responses to Can Sea Urchins Show Scientists How To Capture Carbon Affordably?

  1. Maybe not a silver bullet, but a nickel bullet?

    • Mulga Mumblebrain says:

      Not necessary if we decarbonise, so a sop to the fossil fuel interests. Another five or ten years can be spent proving that the technology works, or it is a chimaera, lovely years of continued mega-profits for the fossil fuel mob.

    • A Siegel says:

      How about the simple question: HOW MANY YEARS FROM NOW?

      Even as I like (love) to learn about potential advances and want (need) positive news, questions:

      Is this little more than a university lab experiment that might emerge decades from now or has this been tested / prototyped at any scale?

      Seems to me that this discussion / post needed to be tempered with some realism about the leap challenges from university lab to real world applications.

      • David Lewis says:

        BBC News quotes co-author Lidija Siller: “You bubble CO2 through the water in which you have nickel nanoparticles and you are trapping much more carbon than you would normally – and then you can easily turn it into calcium carbonate. It seems too good to be true, but it works,”

        The Newcastle University press release quotes Siller “the result was the complete removal of CO2″. The press release states the group has patented the process and are looking for investors. PhD student lead author Gaurav Bhaduri is quoted: “[the nickel catalyst] is very cheap, a thousand times cheaper than carbon anhydrase”

        Chemistry World, i.e.: “Sea urchin inspires carbon capture catalyst” quotes Siller: “‘The current challenge that we are addressing is to quantify the process. We would like to determine the reaction kinetics and exact yields. Once we have this information we plan to do a small continuous process in a lab-scale pilot plant“. CW dug up a skeptic: ‘This work represents an incremental addition to CO2 capture where the catalytic dimension is relevant,’ comments Mark Keane, who investigates catalysis engineering at Heriot-Watt University in Edinburgh, UK. ‘True innovation, however, should harness catalytic action in the conversion of CO2 to high value products, such as carbamates”.

        • David B says:

          I’m honestly a little baffled by how they’re selling this to the public. They are blatantly overstating their case. I’m glad CW looked for a skeptical opinion on this (though I actually disagree with the specifics of his objection). Having read the paper and seen the data I’m cringing over this whole episode. Luckily for them it’s in a relatively small journal, so if it doesn’t work out it will probably just fade. Heck, maybe it will work, but wouldn’t you want to be sure before you tell it on the mountain? There are some very simple experiments that would have made the paper much, much more conclusive.

          • David Lewis says:

            The lead author of this paper, i.e. Gaurav Bhaduri, and Dr. Lidija Siller are posting explanations of their work directly to the Google Geoengineering group.

            They are responding to comments coming from Dr. Ken Caldeira, Dr. Greg Rau, and Oliver Tickell.

            The exchange can be monitored at this address: Nickel catalyst discussion

          • David B says:

            Thanks David. That discussion seems to be proceeding in a murky fashion, haha. In any case, it only addresses questions regarding the application assuming the activity they report is true. My issue is that their data appears not to support their conclusions that they have an active catalyst. I have contacted Dr. Siller directly and haven’t received a response.

  2. Bruce S says:

    The calcium carbonate produced could be put into the oceans to counteract acidification but we are going to need billions of tons. Probably getting ahead of what is feasible but it’s nice to think the lowly sea urchin having 500 million years to work on evolving carbonate chemistry has something to teach us.

    • Jim Baird says:

      Since sea level rise is one of the primary consequences of having too much CO2 in the atmosphere, isn’t it a little counter productive to take a gas to form a precipitate that sinks to the ocean floor?

      Does “Eureka” ring any bells?

      • Bruce S says:

        Jim, if you dump calcium carbonate into the shallow seas it will sink to the bottom and once it is buried 10 centimeters it will stay there a long time. If dumped into the deep it will sink till it hits the carbonate compensation depth where it will dissolve and release it’s Co2 and calcium. It will absorb hydrogen ions and in the process counteract acidification. I don’t know if you are serious about your concerns re. sea level but the feasibility of sourcing billions of tons of calcium ( gypsum) seem unlikely so not to worry. We are still on a trajectory to change the ocean surface water pH by 150% within 90 years. Sea level change in same time frame? A couple feet?

        • Jim Baird says:

          Bruce, as you say you will need billions of tons, which when placed in water will displace billions of tons which have no where to go but up onto the shore. And yes I am serious about my concerns. I have patent applications in the works for five ways to counteract the 69 feet of rise Jason Box says is currently built in. By converting ocean heat to mechanical energy using OTEC, the electrolysis of ocean liquids, the capture of melt water before it enters the ocean (as has been suggested locally for tankering water from Ocean Falls in BC to the US), the movement of surface ocean heat to a depth where its coefficient of expansion is half that of the surface, and the throttling of the movement of tropical heat to the poles by the conversion of this heat to mechanical energy and the movement of surface heat to the deep where it contributes less to sea level rise. The plant life produced onshore by water either desalinated from or that would have otherwise gone into the oceans would provide food, fuel and fiber for the 10 billion living on the planet in a few years. I don’t see that benefit provided by sea urchin.

          • Bruce S says:

            Jim, If ever there were a time to think big this is it. Hats off, but in the process you could add some alkalinity back into the oceans it would be of service.

  3. Photon says:

    Wondering where you would get the calcium? It’d have to be from gypsum, I suppose. Most other common calcium minerals contain carbon, which would of course defeat the purpose entirely.

    Gypsum is CaSO4·2H2O

    I’m no chemical engineer, but pull the Ca out of that and your left with sulfur dioxide, sulfuric acid, or both.

    Can we stop trying to make coal clean now?

    • Mulga Mumblebrain says:

      A veritable Little Ray of Light. Me, I’m a cynic by profession and a sceptic through experience. I smell a fossil fuel rodent lurking hereabouts. Just decarbonise, as fast as possible, and leave the coal in the ground. Oh, no, all that lovely money, going to waste.

    • Omega Centauri says:

      Gypsum, is obviously not a good way to go.

      I presume the Calcium must come from calcium containing silicates (most likely igneous rocks). If so it is a way to speed up the silicate to carbonate cycle, which is our planets thermostat (warmer planet means faster conversion, which reduces Co2, leading to cooling. The natural process is too slow for us, taking maybe a million years to approach equilibrium, so we have to speed it up many fold.

      Obviously with anything like current rates of consumption many cubic kilometers per year would need to be done. I think the scale is unrealistic, although I could imagine some carbon being turned into useful products.

    • charles hollahan says:

      Yes, that’s the consequence of using/making calcium carbonate to control pH in aqueous environments – it leads to the release of carbon dioxide.

      It could be coupled in a system to prevent accumulation though.

  4. bill says:

    So where are they getting the Calcium don’t tell me it’s by heating limestone to drive off carbon dioxide.

  5. David Stern says:

    I looked at the paper. The paper is about catalysis to improve the rate and lower the cost of conversion of carbon dioxide to carbonic acid (H2CO3). The paper doesn’t discuss the source of calcium. The idea of converting CO2 to CACO3 is just a motivation in the abstract and the introduction. It doesn’t mention sea urchins at all. The source of calcium on a large scale is the major issue I think in this idea. CaO is made from CaCO3 usually, so that is pointless.

    • Omega Centauri says:

      The proposed approaches to taking CO2 plus water plus energy to make hydrocarbon fuel, start with carbonic acid in seawater. The Navy would like to do this with Nuclear power on aircraft carriers, to create jet fuel. Maybe this process would make carbonic acid easy enough to create on land (using stranded wind/solar)? The only proposals I’d seen needed a stream of CO2 from a power plant, so at best each carbon atom is used twice. [But if the CO2 came from biomass, maybe we have the makings of something sustainable].

  6. Brian R Smith says:

    Photon & bill,

    “The research team developed a process to capture CO2 from waste gas by passing it directly from a chimney top through a water column rich in nickel nanoparticles. The solid calcium carbonate can then be recovered at the bottom of the column.”

    They’re not any source of calcium, they’re using nickle nanoparticles to catalyze cal. carb. from CO2. The questions are: how much NICKLE do we need per gigaton of CO2? Do we have it? What are the collateral results on that scale? What is the cost? What’s the timeline for delivery at scale?

    Also, perhaps: What effect in seawater?

    • Brian R Smith says:

      David Stern, am I off here? Calcium is required? Anyone?

      • Steven says:

        No, you’re correct. I think they’re getting confused from reading too fast. It uses nickel, as you said, and produces the calcium carbonate.

      • David B says:

        I work in a related field, so my response may not be definitive, but I’d say it’s informed at least. The questions you’ve asked here are exactly the right ones, and probably what the researchers are trying to answer for themselves right now.

        First off, the calcium bit is a red herring. Geologic sequestration is generally envisioned with olivines (magnesium and iron silicates) and similar minerals. We lack a good calcium source that isn’t already a carbonate. Furthermore, calcium carbonate isn’t a particularly stable mineral, and can lose CO2 on heating or slowly at low pH.

        But calcium aside, one of the major challenges in CCS (carbon capture and sequestration) is purification of CO2 from other combustion products. Turning it briefly into a soluble bicarbonate species is one method with excellent potential to achieve that goal more cheaply. At present we lack an excellent catalyst to do it (in biological systems it’s done by the enzyme carbonic anhydrase, but that’s too expensive for industrial application). That’s actually what I work on, and this study proposes an interesting solution.

        Whether this can beat out the current technology depends on the catalyst activity, its lifetime, the cost in producing it, among other economic considerations. The bad news is that nickel is not a cheap metal. It’s ten times the price of lead and zinc and perhaps double the price of copper. That doesn’t mean there’s no chance of feasibility, but it increases the challenge.

        • Brian R Smith says:

          Thanks. Jury’s still out then, but we’ll be lucky indeed if there is at scale sequestration that can be at least a partial solution.

      • David B says:

        Sorry for the double post, but I went ahead and looked at the paper. There are some misleading statements (though they may be honest mistakes) and the CO2 uptake data have a strange inconsistency that is hard for me to understand.

        First, they claim that the rate limiting step (RLS) in CO2 sequestration is hydration of CO2 to form carbonic acid. This may be true under artificial conditions where calcium carbonate is “sequestering” the CO2, but it’s certainly not true in the real world, where dissolution of olivines and similar silicate minerals is the RLS, and happens -much- more slowly. They make this claim a couple times, including in the abstract, and I think it’s fair to characterize it as misleading.

        As to the data, I’m quite puzzled by the “DI water” plots in Figure 5a and 5c. They feature what is sometimes called a “sigmoid” shape: a plateau, then a drop, then another plateau. That is completely inconsistent with what they are supposed to be measuring, which would drop with a gradually decreasing rate, just like the “DI water + NiNPs” in 5a. There is no reason to expect a delayed drop like that. This signals a major problem with their experiment that will have to be addressed before the results can be trusted. I’m worried the press release on this way overstates their case.

    • Mulga Mumblebrain says:

      And nanoparticles have been shown to be completely harmless, by loads of research, haven’t they?

      • Brian R Smith says:

        You have a point there.

      • David B says:

        Indeed :) Though it should be pointed out that the chemicals currently used to separate CO2 in natural gas mining (and currently the cheapest option to do it for flue gas) are highly toxic and corrosive. A better solution is sorely needed.

      • Omega Centauri says:

        They did make the claim, easily separated out and reused. For both economic and ecological reasons, the leakage rate (of Nickel) would have to be pretty low.

        Because of the nanoparticle concerns, adding nanoparticles to mine waste rock to speed up carbonate formation is probably a no go.

    • Artful Dodger says:

      Brian, you do understand that nickel is used as a catalyst in this process? And the used catalyst is recovered magnetically for reuse? It is misleading to think of Ni consumed per gigaton of CO2 sequestered. At this point, this is a science project. Perhaps you should study more about the basic science rather than focusing on the non-existing technology.

      • David B says:

        Pretty harsh response to some pretty reasonable questions..

        Every catalyst has a lifetime. There is some degradation pathway into something. With nanocrystals that is often aggregation or sintering, whereby the nanocrystals cease to be nano anymore. Then the question is, what does it cost to make them nano again? If there are other degradation pathways, such as oxidation, you have to consider how to reverse those as well. And at the scale we’re talking about, you are still going to need much much more catalyst than for a typical industrial process, so the price and availability of nickel is quite relevant.

        This all isn’t to say the science shouldn’t proceed (it certainly should), but it’s never a bad idea to anticipate stumbling blocks.

      • Brian R Smith says:

        You’re quite right, I do lack the basic chemistry for this & should probably bugger off. The paper is paywalled for me, so I am relying on third hand information that, as far as I can find, mention nothing about introducing calcium into the process. I didn’t know enough to realize it would apparently have be there. Nor did I get that the Ni is completely recovered (which seems like chemical perpetual motion to my untrained eye). And it may be a stretch to call this a real technology, as opposed to “non-existing”, merely because the team is peer reviewed and has a patent. I’ll just slip into the background….

  7. Chris says:

    I’m always very suspicious of plans like these. As those above noted, where are you going to get the calcium. Theoretically you could use another element. Also where do you put it? I know they say CaCO3 can be used as a building material, but we are spewing gigatons of CO2 into the atmosphere every year. That would mean we’d need gigatons of calcium every year. That is a lot of plaster casts.

  8. Paul Klinkman says:

    In the end, the carbon dioxide capture idea could be a bit of progress. There’s still a big issue. It’s the same issue that an idea for a car that gets 500 mpg on a gallon of water would have. Where do you get the energy?

    If you want to bubble 10% carbon dioxide, 10% oxygen and 80% nitrogen through a column of water, where do you compress the gases to get them to the bottom of the column?

    Once you capture calcium carbonate, you probably want energy to convert it back to pure carbon and pure calcium. If you have solar power or wind power, this second step can wait a few hours or days until the sun shines or until the wind blows.

    In a coal company’s dream you’d plow the charcoal into nearby topsoil, but what happens when all the nearby topsoil is well-carbonized? Then a dump truck needs to haul the carbon off to some carbon sequestration landfill.

    Next question: if you have 395 ppm of carbon dioxide, can you bubble that through a water column? The answer is yes, and why not. You could do this where solar power is cheap, out in a desert, and you could bury the carbon cheaply.

    • Omega Centauri says:

      IIRC (not a chemist either) the carbonation reaction is endothermic (gives off energy). So energy isn’t a showstopper. Of course any industrial process requires some form of energy. But its probably more a question of economics and scale, then of whether it works on paper.

  9. From Peru says:

    From the news release:

    “At present most carbon capture and storage (CCS) proposals are based around the idea of capturing CO2 (…)power plants and pumping the stripped out gas into underground storage (…)

    The Newcastle researchers say that an alternative approach would be to lock up the CO2 in another substance such as calcium carbonate or magnesium carbonate. This can already be done by using an enzyme called carbon anhydrase but it is very expensive.”

    This is not what carbon anhydrase do. Carbon anhydrase catalyses the conversion of CO2 dissolved in water into carbonic acid, that then dissociates to bicarbonate(HCO3-) plus hydronium(H+) ions, and also the reverse reaction. This is the reaction:

    CO2(aq) + H2O(l) = H2CO3(aq) = H+(aq) + HCO3-(aq)

    It is slow without catalysts, but carbon anhydrase accelerates it. This enzyme enables organisms to rapidly absorb and/or liberate CO2, for example, without it we will die from CO2 poisoning, since the enzyme speeds up CO2 absorption in the bloodstream and its liberation to air in the lungs. Here is a good review in PNAS:

    http://www.pnas.org/content/70/9/2505.full.pdf

    However, turning CO2 into H2CO3 it just turns carbon dioxide into carbonic acid (and viceversa). This is useful to separate the CO2 from the mix of gases that made the smoke of power plants , obtaining clean air and a “carbonic acid concentrate”. The structure of a carbon capture facility is shown in the BBC news release:

    http://www.bbc.co.uk/news/science-environment-21320666

    With this discovery, it will be cheaper to “concentrate” CO2. A good starting point , but not enough to actually “capture” carbon because carbonic acid is not stable. To capture CO2 you must turn into a stable form, like calcium carbonate (CaCO3) or magnesium carbonate (MgCO3).

    This is the classic thermodynamics vs. kinetics issue. There is no catalyst that can do the trick. That is impossible because catalysis is about the speed(a.k.a. kinetics) of reactions , not about the direction of them (i.e. the fact that the reaction can occur or not, a.k.a. thermodynamics). Calalysts just speed up already (thermodynamically) feasible (but slow) reactions.

    To precipitate CO2 into a stable solid you need a base to neutralize the carbonic acid. The two most useful industrial bases are sodium hydroxide (NaOH) and calcium oxide(CaO). Unfortunately the production of them is energy-intensive and in the case of calcium oxide… well the equation showing the production of it by calcination says it all:

    CaCO3 + heat = CaO + CO2

    • From Peru says:

      The best bases avaivable that can work are the calcium(or magnesium) silicates, like olivine (Mg2SiO4), enstatite (MgSiO3) or wollastonite(CaSiO3), just to name a few. The reactions are:

      Ca(Mg)SiO3(4) + H2CO3 = SiO2 + Ca(Mg)CO3

      The rapid transformation of carbon dioxide into carbonic acid can help this reaction, but nothing about that is said in the news release.

      There is also calcium carbonate, that can also neutralize carbonic acid into calcium bicarbonate:

      CaCO3 + H2CO3 = Ca(HCO3)2

      Calcium bicarbonate is more stable than carbonic acid, but it is still highly soluble in water so cannot be sequestered into a solid product. If the water is acidified by any acid, the CO2 can be liberated.

    • David B says:

      This is an excellent, technically accurate summary. Thanks, From Peru. I would only add that the silicate reaction in your reply is thermodynamically favored, but is limited by the rate of dissolution of the silicate at most pHs. (Not to say you don’t know that, but readers may be confused by the thermo/kinetics but in your prior post.)

  10. Joan Savage says:

    Calcium hydroxide or calcium-ion-enriched fresh water are likely possibilities for testing. The nickel catalyst seems cheap, but I’m very skeptical about the technique’s ability to keep nano-nickel out of the food chain and the environment in general. Don’t want plant respiration inhibited. Don’t want little plaques of calcium carbonate forming in one’s lungs.

    Calcium-depleted water on an industrial scale is also something to mull over.
    But then I’m cautious.

    Leaving coal in the ground and conserving electric use doesn’t push us as hard into unfamiliar consequences.

  11. Anne says:

    Wow, what a great dialogue on a fun chemistry problem for a very serious problem much in need of a solution. As a trained environmental chemist, but who switched over to policy/politics early on, this is precisely the sort of discussion that needs to be taking place in much grander forums, every day. The over-arching problem, as I see it, is that even IF the discovery that nickel-as-catalyst is a scientific breakthrough (though I find it hard to believe this would be news to those who have been searching for a way to sequester CO2 from smokestacks), we would need a fast-track RD&D program, with field tests, and gov’t-private sector cost-sharing, to see if there’s a way to turn CO2 into solid CaCO3 “chalk” before the CO2 is emitted into the atmosphere. As for Ca sources, it’s a common element found in limestone (karst topography), sedimentary rocks, and bones. It’s likely used in industrial processes in various forms and a market demand would cause a market supply. Again and again, we’ve seen new federal and state laws create thriving markets (e.g. the catalytic converter in every automobile). The chemistry of this sounds simple to me, or at least, manageable. The problem will be, as it almost always is, the limiting factor of political and market will, and cost. Unless and until we put a price on carbon, there is no driving factor to make this “chemical reaction” go. Put another way, we need to light a bunsen burner under the coal industry execs, and making it a lot more expensive to emit carbon dioxide is the best way to light that fire. (My view, anyway.)

    • Anne says:

      One more quick comment — one of the commenters here said: “The paper is paywalled for me, so I am relying on third hand information that…” This is a serious problem — scientific journal articles are prohibitively expensive for the lay person or even scientists not affiliated with universities or large corporations willing to pay the subscription fees. Let us be reminded of Aaron Swartz, who took his own life because he was being aggressively prosecuted by DOJ for downloading scientific papers from JSTOR. We need OPEN ACCESS, or some degree of it anyway, so that people like me, people like CP readers, can read the original paper that these news stories were based on, and see for ourselves what they say. The authors of this sea urchin-nickel-CaCO3 paper know nothing at all about coal burning and CO2 emissions. Leaping to conclusions from new findings in one scientific discipline about potential applications in a completely different scientific discipline is dangerous and requires sophisticated interdisciplinary examination. If more of us had access to scientific journal articles and made a point to read them, more and more of these cross-over ideas would pop up and perhaps we’d make more headway in solving today’s tough problems. RIP Aaron Swartz, and thank you for all you did to keep the internet intact and to call attention to the “paywall” that keeps us from being able to read about all the wonderful scientific discoveries happening every day.

  12. Excellent discovery I must say! This really could be end to all the doom and gloom of greenhouse gases and provide a real solution to reduce CO2 in our atmosphere, from the humble sea urchin! In the meantime, it is important for households and businesses to look to reduce emissions and their carbon footprints. I work for a company where this is particularly important and at the top of the agenda: Nviro’s CO2 footprint

  13. Reading the article and the comments, I just had and idea: Given that CO2 concentration in the ocean should be lowered to save pH sensitive species/diversity, how could humans accomplish this? Even very simple industrial plants would take too many resources to build enough to make a difference. Bioengineering a fast growing animal, like the Sea Urchin would upset ecological balance. Putting such genes in a bacteria would lead to blooms and remove too much oxygen.

    Perhaps these carbon fixing genes could be put in cyanobacteria or in an algae. These might have difficulty competing with the native species, but maybe they could also be changed to be more acid loving. Even if only a low % of these “plants” (compared to native) could spread to large areas of the ocean, they might fix enough carbon to make a difference. It seems that zooplankton that grow calcium carbide structures would like to eat these plants to get the calcium carbonate without having to make it themselves. Perhaps the zooplankton could also help with the carbon fixing “plants” reproduction.

    Another idea is to make the CaCO3 zooplankton more acid or even heat tolerant so more would grow. Whales should appreciate this change!

    • From Peru says:

      Not so fast!

      Calcification is actually a SOURCE of carbon dioxide, not a sink. Here is the equation:

      Ca(HCO3)2(aq) = CaCO3(s) + CO2(aq,g) + H2O(l)

      or:

      calcium bicarbonate (aqueous) = calcium carbonate (solid) + carbon dioxide (aqueous or gas)+ water (liquid)

      This is a counter-intuitive, but true fact: all calcium carbonate-producing organisms actually emit CO2 when they make their shells from calcium bicarbonate dissolved in the water.

      To “fix” carbon you need a base. Silicates of calcium and/or magnesium are the most common natural ones.

  14. Bob Wright says:

    As long as there is new calcium from weathered minerals, the process does net take dissolved CO2 out of ocean water. The real problem is a man made calcium source that doesn’t put more CO2 into the environment than it is worth.