Detailed Description of the Idea

This is a detailed description of the idea. There is also a a briefer description and a a slideshow presentation on the process.

A Concept Process for the Sequestration of Carbon Dioxide, the Mitigation of Ocean Acidification and the Production of Biomass in Arid Environments


The concept process outlined has the potential to reduce the concentration of carbon dioxide in the atmosphere to pre-industrial levels. The process works by thermally decomposing (calcining) limestone and adding the resulting calcium oxide to seawater, thereby increasing the capacity of the oceans to act as a carbon sink, whilst at the same time mitigating ocean acidification. The carbon dioxide generated by the thermal decomposition (calcination) of limestone can be sequestered, or utilized either as the starting point for the production of fuels, or to enable biomass to be grown in arid environments, without the need for irrigation. The process thus addresses a number of environmental and social problems: climate change, ocean acidification, food shortages, fuel shortages, water shortages and soil salinification from excessive irrigation.


The world’s oceans act as a carbon sink absorbing about 2 billion tonnes of carbon (2GtC) from the atmosphere each year, thereby helping to slow the rate of increase in the concentration of atmospheric carbon dioxide. Whilst this helps slow climate change, the additional carbon dioxide dissolving in seawater causes ocean acidification – a reduction in the pH of the oceans, which threatens the viability of marine biosystems.

The concept process outlined in this paper seeks to simultaneously enhance the capacity of the oceans to act as a carbon sink and to mitigate ocean acidification, by adding calcium oxide to seawater. The source of the calcium oxide is limestone. By heating limestone until it thermally decomposes, calcium oxide and carbon dioxide are generated. On addition to seawater the calcium oxide reacts with carbon dioxide dissolved in the water to generate calcium bicarbonate solution.

The key aspect of the concept process is that each mol of calcium oxide acts to enhance the capacity of the oceans to absorbs two mols of carbon dioxide from the atmosphere at dilute concentrations (387ppm), whilst, to produce the calcium oxide, only one mol of pure carbon dioxide is generated.

Pure carbon dioxide has several advantageous properties that carbon dioxide at atmospheric concentrations does not have – it is easier to sequestrate, it can be used as a feedstock for the production of fuels and it allows the production of biomass in arid environments.

Utilizing this ‘carbon negative’ process has the potential to reverse the accumulation of carbon dioxide in the atmosphere and it would be possible to reduce atmospheric carbon dioxide levels to pre-industrial levels.

Origination of the Idea

Whilst this idea was developed independently, it has recently been brought to our attention that a very similar idea was put forward in a paper by Haroon Kheshgi in 1995 (Kheshgi HS “Sequestering atmospheric carbon dioxide by increasing ocean alkalinity”, 1995, Energy 20, 915-922). He concluded that “this approach appears to be limited only by the availability of energy” – it is this constraint that we are hoping that we are able to address.

The concept of using carbon dioxide generated from the calcination of limestone to enable the production of biomass in arid environments is, as far as we are aware, original.

Calcinination of Limestone

It seems counter-intuitive to attempt to counter climate change by heating limestone. For a start the process is highly energy-intensive – to calcine limestone requires a temperature of 850C and consumes 2.67GJ per tonne of limestone calcined. Also, when the limestone (CaCO3) decomposes it generates carbon dioxide:

So it is doubly damaging – the energy-intensive process results in carbon dioxide production (assuming fossil fuels are used to drive the reaction) and carbon dioxide is emitted as a product of the process.

In order to derive pure carbon dioxide from the calcination of limestone it will not be possible to use conventional lime kilning processes as these co-fire fuel, air and limestone, resulting in a flue gas which contains large quantities of nitrogen. Instead one of two novel techniques will need to be employed:

  • Co-firing fuel, oxygen and limestone in a conventional kiln. (It may be necessary to dilute the fuel oxygen mix with carbon dioxide, which will lower the burn temperature that would otherwise result – if the temperature is too high, the calcium oxide generated will sinter)
  • Separating the heating process from the calcining process. A fluid, potentially molten iron or water vapour, is heated within a sealed vessel by the combustion of the fuel in air external to the sealed vessel. The limestone is calcined in or on the heated fluid. The flue gases of the two processes (combustion and calcination) are treated separately with the flue gas from combustion having a low carbon dioxide content, whilst the flue gas from the calcination is pure carbon dioxide.

Addition of Calcium Oxide to Seawater

If, however, the calcium oxide generated is added to seawater (either directly, or more probably, first reacted with water to form calcium hydroxide) then it reacts with carbon dioxide dissolved in the seawater to produce calcium bicarbonate:

Note that at the pH levels present in seawater, the bicarbonate ion (HCO3-) is by far the dominant ion formed, rather than the carbonate ion (CO32-). Thus for every mol of carbon dioxide generated from the calcination of limestone, approximately 1.79 mols of carbon dioxide are sequestered when the calcium oxide is added to seawater, a net sequestration of 0.79 mols of carbon dioxide. The exact amount of carbon dioxide sequestered will depend upon the exact conditions (including pH, temperature and pressure) where the reaction takes place.

The addition of calcium oxide to seawater leads to the sequestration of carbon dioxide, by enhancing the capacity of the oceans to act as a carbon sink. It does this by shifting the series of equilibria (below) to the right, thereby increasing the capacity of seawater to absorb carbon dioxide from the atmosphere and by decreasing the propensity for seawater to desorb carbon dioxide into the atmosphere.

At the same time as sequestering carbon dioxide, the addition of calcium oxide to seawater will cause the pH to increase, thereby mitigating ocean acidification. Care will need to be taken to ensure that the way in which the calcium oxide is added to the seawater does not lead to excessive localised increases in pH.

Treatment of Carbon Dioxide

There are several options for treating the carbon dioxide generated from the calcining of limestone:

  • The first option is to simply release it into the atmosphere. This may seem counter-productive – we are after all trying to remove CO2 from the atmosphere – but given that adding calcium oxide to seawater removes nearly twice as much CO2 as is generated in the calcining process, this may be the most economic route.
  • The second option is to sequester the carbon dioxide using existing techniques (e.g. in saline aquifers, disused oil wells, etc). It should be noted that the costs associated with the sequestration of carbon dioxide from the flue gases of a fossil fuel power plant are primarily associated with the separation out of carbon dioxide from the other flue gases and the cost of sequestering the pure carbon dioxide are low in comparison. The carbon dioxide generated from the calcining of limestone will be relatively pure and no separation will need to be undertaken.
  • The third option is to use the pure source of carbon dioxide as a starting point for the production of fuels. Various techniques are already known, whereby with the addition of heat energy, carbon dioxide can be split into carbon monoxide and oxygen:

Carbon monoxide can be reacted with water to produce hydrogen using the gas shift reaction:

This hydrogen could be used as a fuel in itself, or as a starting product for the production of other chemicals including hydrocarbon fuels by reacting it with carbon monoxide derived from the previous reaction in Fischer-Tropsch reactions.

Alternatively the carbon monoxide could be dissociated into carbon and carbon dioxide via the Boudouard Reaction:

The carbon yielded could either be sequestered (by burying) or could be used as a fuel in conventional coal-fired power stations. The carbon produced would be of greater purity than coal as it would not contain pollutants such as sulfur and heavy metals.

  • The fourth option is to use the carbon dioxide to enable biomass to be grown in arid environments, without the need for irrigation. Carbon dioxide is introduced into a transparent, sealed vessel which is filled with water and contains algae where photosynthesis will occur in the presence of sunlight.

nCO2 + nH2O –> (CH2O)n + nO2

Carbon dioxide and water are converted into sugars and oxygen.

Because the system is sealed, water loss will be minimal. One potential source of water loss could occur when the oxygen generated during photosynthesis is vented from the system – it is necessary to vent the oxygen to avoid a build-up of pressure. If water is particularly scarce it may make economic sense to dry the vented oxygen to recover any water vapour from it. Note that were ambient air containing carbon dioxide at 387ppm used instead of pure carbon dioxide, over 2500 times the volume of gas would need to be dried to deliver the same amount of carbon dioxide, without the loss of water vapour.

The production of one mol of glucose (C6H12O6) (180g) involves the consumption of six mols of water (108g). Thus for each kg of glucose produced 600g of water are consumed.

Were such a system to yield 10 tonnes of glucose per hectare per year (comparable to the yield of a conventional sugar cane plantation), then 6 tonnes of water would be consumed. As a single millimetre of rain falling on a hectare amounts to 10 tonnes of water, it can be seen that such a system could allow the production of crops in all but the most arid of environments, even allowing for the loss of some water from the system (cf the average annual precipitation in the most arid parts of the Sahara is 40mm per year).

In comparison, to grow crops in arid environments using conventional irrigation often uses over 1000 tonnes of water per tonne of dry crop yielded.

The crops yielded could be used for human or animal consumption, or be utilised to produce biofuels. It could be possible to have algae photosynthesizing at the top of the vessel (in the sunlight) and dead algae falling to the bottom of the vessel, where they would be decomposed by bacteria in anoxic conditions to yield methane which would be combusted with the oxygen vented from the system to provide the heat energy required to drive the calcination of limestone.

In addition to lacking water, deserts are often hostile environments for plant life because they suffer from extreme temperature swings. Night-time temperatures can be close to freezing point and peak day-time temperatures can cause scorching. Having a large body of water in a sealed container provides a high heat capacity, resulting in less dramatic fluctuations in temperature. This would allow the system to operate at a temperature that is more amenable to plant growth throughout the day. Normally, employing large quantities of water in a desert environment to stabilize diurnal temperature swings would be extremely wasteful as it would rapidly be lost by evaporation to the air, but as the system is sealed, water will not be lost.

Another advantage of having a system that is sealed from the air includes the ability to prevent competitor organisms, disease and predatory organisms from entering the system. The carbon dioxide entering the system would be automatically sterile as it is the product of the calcination of limestone, which occurs at 850C

As well as reducing water requirement, the system described has an additional advantage over irrigation in that it will not result in an increase in soil salinity, which is a frequent consequence of heavy irrigation.

Providing the Energy to Drive the Calcination Reaction

It is anticipated that ‘stranded energy’ could be used to provide the energy required to drive the calcination of the limestone. Stranded energy is energy that is too remote from a possible market to make it economically viable to transport it to that market. For example, stranded gas is natural gas which would cost more to deliver to a market than it would earn on reaching that market. Solar energy, whilst abundant in the Sahara desert is stranded there, because there is scant demand there and to transport the energy to where it is wanted would be too expensive. Large amounts of energy available to us are paradoxically both free and worthless.

  • Using stranded gas may at first sight seem counterproductive – after all burning methane generates carbon dioxide. But calculations show that 0.3 mols of methane would need to be combusted to cause a mol of calcium carbonate to calcine. Thus a total of 1.3 mols of carbon dioxide would be produced (0.3 mols from the combustion of the methane and 1.0 mols from the calcination of the limestone) per mol of calcium oxide generated. That mol of calcium oxide when added to seawater will absorb 1.8 mols of carbon dioxide, giving a net sequestration of 0.5 mols of carbon dioxide. If the carbon dioxide generated from the calcination is sequestered a net 1.5 mols of carbon dioxide will be sequestered per 0.3 mols of methane used – a ratio of carbon dioxide sequestered to methane used of 5:1
  • Another source of energy that could be used for driving the calcination of limestone is from nuclear processes. If the desired output from a nuclear plant is process heat rather than electricity, then the cost of the plant can be significantly reduced as there is no requirement for power generation or transmission equipment.

Using Dolomite or Magnesite as an Alternative to Limestone

In addition to limestone (CaCO3), dolomite (CaMg(CO3)2) and magnesite (MgCO3) could be used. Limestone calcines at 850C, whilst magnesite calcines at 350C – dolomite undergoes two partial calcinations events at 350C and 850C. Whilst magnesite calcines at a much lower temperature it is less abundant than calcite and the magnesium oxide yielded is sparingly soluble in seawater making the sequestration of carbon dioxide more problematic.

Nullarbor Plain as a Potential Site

One location where this process would be feasible is in the Nullarbor Plain, in Australia. An area of scrub with annual rainfall of between 200-300mm and solar irradiation of approximately 20MJ per m2 per day, it is a sparsely populated piece of limestone 200,000km2 in extent. Calculations show that to remove a billion tonnes of carbon from the atmosphere would require the disposal, through this process, of approximately 1.5km3 of limestone (assuming the carbon dioxide generated in the calcination of the limestone is successfully sequestered). Given that there are approximately 10,000km3 of limestone in the Nullarbor Plain and that humankind have emitted a total of 305GtC between 1750 and 2003, it would require the consumption of approximately 5% of the limestone in the Nullarbor Plain to return the concentration of carbon dioxide in the atmosphere back to pre-industrial levels.

To offset current emissions (in the region of 7GtC per year) would consume 10.5km3 per year and require some 80 billion GJ of heat energy – equivalent to a power output of 2500 GW. At double that power output, the amount of carbon dioxide in the atmosphere could be reduced back to pre-industrial levels in about forty years.

Intellectual Property Situation

The calcination of calcium and magnesium carbonates and addition of the resulting oxides to seawater as a method of carbon dioxide sequestration is mentioned in the description of patent application PCT/US2005/015453, but there are no claims in the application referring to that part of the description. Given the time that has elapsed since the original filing, there is no prospect of the grant of a patent anywhere in the world, except for possibly in the United States. Given the previous work by Kheshgi, it would seem that this part of the application would not pass the novelty test, so there is little prospect of any patent restrictions on this process.

The authors of this article are not seeking patents on any aspect of the process and wish to develop the process in an open source manner.

If you would like to help develop this project, please click through to find out how you can get involved.


38 people have left a comment

anonymous says: July 21st, 2008

Interesting idea.

But you want to do all this using stranded resources. Those resources are stranded for a reason– they are in the middle of nowhere. What is the energy cost of transporting thousands of tons of rock from the middle of nowhere to the nearest ocean (or more accurately, to all the oceans of the world, so you don’t cause a local increase in alkalynity)? What makes you think it is easier/cheaper to transport thousands of tons of rock than to just ship the electricity?

Jonathan McCabe says: July 22nd, 2008

Why does the CaCO3 need to be converted to CaCO and CO2 before being added to the seawater?
It seems much easier to just add it directly and get half of the CO2 uptake as from the proposal, just the second reaction of carbonate to bicarbonate.

Robert Merkel says: July 22nd, 2008

Anonymous: the Nullarbor Plain is located on Australia’s southern coastline. Transporting material to the coastline would be a simple exercise.

The scale of the project is mind-boggling, but doable on a global (particularly as it doesn’t have to be built in one hit or in one location). 2500 GW of electricity from nuclear power (for example) would cost in the order of 6-7 trillion dollars – a lot of money, but only about 10% of the world’s annual GDP (in reality, of course, such a project would be spread over many years). Given that you want thermal energy, not electricity, you could probably get away with a third of that.

Richard says: July 22nd, 2008

Don’t ships take on sea water at one port for balast then vent it later at another?
Could they “sprinkle” the oceans with lime as they go?

Henri says: July 22nd, 2008

“To offset current emissions (in the region of 7GtC per year) would consume 10.5km3 per year…”

In order to achieve this capacity, the processing would have to be able to handle abt. 57.000.000 tonnes of limestone per day. That’s a lot of limestone.

Just for comparison, the largest ships capacities stand somewhere around 550.000 tonnes. The largest mining trucks can transport about 400 tonnes.

The project is achievable if transporting the material by any vessel is forgotten. Is there any way the limestone could be processed at its natural place? Is it possible to direct the seawater (or water altogether) there for the reaction?

James Clements says: July 22nd, 2008

Use concentrated solar thermal heat generation to produce the lime. No extra CO2 generated and solar thermal would work very well in sunny/desert isolated regions. Solar thermal is a proven technology generating gigawatts of power around the world. The issue then becomes transporting the raw materials to the solar thermal plant and transporting the lime to the ocean.

per says: July 22nd, 2008

What about using the CaO as an corrosion inhibitor in the following indirect solar energy harvesting scheme(cold seawater mist downdraft tower):

Evan says: July 25th, 2008

That sounds like a great idea.
But it also need to consider how to implement.How to transporting rocks and so on.not a simple thing.Needs the numerous countries and the International organization unites and efforts together.

qwerty says: August 4th, 2008

What happens to Ca(HCO3)2 in the oceans?
What happens to plants and fish if you heavily increase the concentration of Ca(HCO3)2 ?
Did you calculate the increase of CO2 of a dying underwater biosphere?

Let’s hope for a moment your idea does not cause a sea life genocide: How much tons of CaO do we talk about, that you have to produce to see a relevant effect? How high will the local atmospheric pollution with CO2 be at the plants that produce CaO ?
Do you know that at 1% of CO2 in the atmosphere people start to die?

Chris Unitt says: August 4th, 2008

Thanks for the thoughts and comments here so far.

qwerty – those are exactly the sorts of questions we’re trying to find the answers to. If this process is to be put into action then it must be done without risk to the environment – we’re trying to make things better, after all.

If anyone has any information about this then please let us know over here –

yer says: August 19th, 2008

If possible, never tinker with a system which provides us with vast amounts of resources. Utilizing non-valuable resources would be a safer one.

Tim Kruger says: August 20th, 2008

Yer – the problem is that we have already tinkered with the system that provides us with vast amounts of resource – the biosphere. In an ideal world we would stop producing carbon dioxide and the climate would remain stable, but in the real world that is unlikely to happen. We need to work out what is the best ‘medicine’ to cure the problem. Doing nothing is not a safe option – unfortunately we are in a position where we have to choose between a number of less that perfect solutions.

Small Blue Planet » Blog Archive » Geo-Engineering - Science for the End of Days says: December 1st, 2008

[…] is a brief description of the idea. If you prefer we also have a detailed description and a slideshow presentation on the process for you to […]

Jem Cooper says: December 15th, 2008

I believe the problems of capturing and sequestering carbon dioxide from the manufacture of calcium oxide are easily soluble. Personally I would start with the pure oxygen option so that carbon dioxide can be condensed from the pressurised flue gas and then pumped underground into suitably impervious rock structures. All the chemical engineering is straight forward and tested, though not in this particular combination. Such a process is needed anyway to deal with the substantial carbon dioxide emissions from the vast existing calcination industry.

The more difficult problem I believe is to prevent precipitation of calcium carbonate as the calcium oxide is added to the ocean. This would halve the potential capture of carbon dioxide as calcium bicarbonate. The upper 1000 metres or so of ocean water are already supersaturated with calcium carbonate; by a factor of over 4 on the solubility product in the upper layers. My guess would be that the processes that inhibit precipitation would be overwhelmed at higher values (perhaps exceeding 10). Potentially precipitation of added calcium as the carbonate could seed the precipitation of the already dissolved calcium carbonate but I think this would happen already if it were likely. When reverse osmosis desalination is practised organic inhibitors are added to prevent calcium carbonate fouling of the membrane. Some very simple scoping experiments mixing calcium oxide and seawater suggest themselves.

I have not done the calculations to see how much of the added calcium would be precipitated as calcium carbonate before getting down to a factor of 10.

A secondary problem is that even if the high pH was tolerated, photosynthesising organisms (and everything further up the food chain) in the zone where the calcium oxide was added would die through lack of carbon dioxide in the water. This is certainly a problem where lime is released in the effluent entering rivers. Because the normal concentrations of carbonate ions in ocean water (about 2000 micro moles per kilogram) are so low very substantial dilution of calcium oxide is needed to get beyond these issues. This is difficult because very large quantities must be added to have a significant impact on the net rate at which we are adding carbon dioxide to the atmosphere.

I have just published a patent (GB 2447513) on addition of limestone to the ocean. Unfortunately because it can only dissolve at great depth there is a long time to wait till the extra dissolved calcium rises to the surface and impacts on atmospheric carbon dioxide. I was, even before reading your article, planning to do some sums on the use of quick lime as an alternative in the manner you suggest. The economics are certainly not prohibitive. I corresponded with Haroon Kheshgi briefly last year but he did not respond to my query as to why he had not pursued his ideas.

Chris Brodeur says: February 21st, 2009


i love this idea and have actually started a high school science projects related to this idea and calcium hydroxide concentrations.
I was wondering how much calcium hydroxide you are talking about mixing into the water or if this has even been pondered yet?
thank you

Jem Cooper says: March 28th, 2009

The cost of quicklime is not a major problem. The average cost of quicklime in the USA at the factory gate was $84/ton in 2007. Shipping cost is say $12/ton. The IPCC Special Report on Carbon dioxide Capture and Storage gives a cost of $30 to $90/ton of carbon dioxide emissions to be avoided, based on capture from a power station and underground storage. This gives a delivered cost for quicklime produced without carbon dioxide emissions of $129 to $195/ton. Even at today’s exchange rate of 1.4 $/£ that is only 19 pence per litre of petrol (using the average quicklime cost) which looks reasonably affordable compared to recent gyrations in forecourt prices.

Lime can be used to treat municipal wastewater prior to release and is often employed in fish farms, but when added to rivers at the limit of its solubility the high pH is likely to kill all life. Even at much lower concentration lime would probably create dead zones due to carbon dioxide depletion which prevents the photosynthesising organisms at the bottom of the food chain thriving. It would take 2% of the flow of all the rivers in the world to dissolve enough quicklime at the limit of solubility to remove one thousand million tonnes of carbon dioxide from the atmosphere. I doubt if pollution on this scale would be acceptable for such a modest reduction in atmospheric carbon dioxide. But in the vastness of the ocean, local temporary loss of fauna and flora may not be such an issue as the addition zone will be repopulated as it is diluted.

Adding limestone (calcium carbonate) rather than lime (calcium oxide) presents none of these problems because it quickly sinks (see my patent GB 2447513 page 10) below the upper ocean layer, where most of the life and all photosynthesising organisms live. Because the limestone sinks not as individual particles but as a dense plume (like the inverse of hot smoke from a chimney) it takes all the water it has mixed into with it. Even at depth it takes years to dissolve and has a very marginal impact on alkalinity. The problem is the time it takes to resurface and impact the atmosphere.

Adding quicklime to seawater also increases its density and potentially it could easily sink well below the upper ocean layer where it can absorb carbon dioxide from the atmosphere. But this issue can probably be addressed by confining additions to seasons and areas of the ocean where there is a strong temperature gradient in the upper layer and by discharging the quicklime much more slowly and thus over a wider area.

Every schoolboy doing chemistry knows that limewater (dissolved calcium oxide) goes cloudy in the presence of carbon dioxide. This cloudiness is precipitated calcium carbonate. Similarly calcium carbonate is likely to precipitate when quicklime is added to seawater which is already supersaturated in dissolved calcium carbonate and contains dissolved carbon dioxide in the form of bicarbonate. It is not possible to dilute quicklime in seawater without passing through regimes of extreme supersaturation, however briefly. Apparently limewater can be added to saltwater aquaria without precipitation but only if it is added very slowly a drop at a time. Such a method would be very difficult to replicate when discharging hundreds of thousands of tonnes from tankers thousands of times a year.

Calcium carbonate precipitation reduces the molar efficiency of added quicklime because much more carbon dioxide can be absorbed in the ocean by keeping the calcium in solution in the predominant bicarbonate form rather than by precipitating it as the carbonate. The upper ocean layer is currently supersaturated by a factor of about 4 on the ion multiple. The stability of this supersaturation is the thermodynamic corollary of the slow dissolving rate elsewhere; at equilibrium saturation, precipitation rate and dissolving rate must be equal to each other. It has been hypothesised that the very slow precipitation rate is due to interference from magnesium ions and/or organic compounds found in the seawater.

Fossil evidence suggests that in long gone times (over a hundred million years ago) the calcium carbonate ion multiple in the ocean was ten or more times the saturation value. Changes in the chemical composition of the ocean have brought down the atmospheric carbon dioxide concentration from 1500ppm over the last hundred million years, initiating the ice ages towards the end of that period. Refer ‘History of carbonate ion concentration over the last 100 million years by TOBY TYRRELL and RICHARD E. ZEEBE. This paper was the inspiration for my limestone proposal.

Paradoxically adding quicklime to the ocean can reduce the calcium concentration and alkalinity even if calcium carbonate precipitation stops long before the ion multiple reaches the current value of about 4 times saturation. This is because the carbonate ion concentration increases dramatically at the expense of bicarbonate as the carbon available in the seawater in the immediate vicinity is spread more thinly trying to balance the extra charge from all the added calcium ions. Subsequent absorption of carbon dioxide from the atmosphere will not redissolve the precipitate.

If precipitation ceases when the ion multiple falls below 10 times saturation it is calculated that 40% more calcium precipitates than was added based on a water temperature of 2C. This would reduce the molar efficiency of the eventual removal of atmospheric carbon dioxide to just 0.68 moles per mole of added calcium oxide and increase the cost to 50 pence/litre of petrol.

I think it is high time somebody did some experiments adding calcium oxide or solid hydroxide to seawater and measuring how quickly and how far it must be diluted to avoid calcium carbonate precipitation and if not avoided how much precipitates. Was Chris volunteering?

He asks how much calcium hydroxide. Current global carbon dioxide emissions from fossil fuel are about 27,000 million tonnes per year so anything less than 1000 million tonnes removal would be insignificant. At a molar efficiency of 177% that would require 950 million tonnes of calcium hydroxide.

Chris Brodeur says: April 12th, 2009

I am currently working on my research paper, yes i have finished the project, and i will post it in the next week.

SK Subramanian says: October 30th, 2009

Ocean floor survey for lime stones may be another area to be searched for which will reduce transportation cost.Lot of solar heat is available on ocean too

Steve Gerrish says: February 26th, 2010

The net effect of this route is the addition of significant amounts of the elements calcium, carbon and oxygen to sea water. Is the same amount of calcium and carbon being precipitated in some insoluble solid form at the other end of this process? (It doesn’t matter where the oxygen goes, either up or down.) If not, then the composition of the oceans will be changed if we are to have any significant removal of CO2 from the atmosphere. What will be the implications of this? I think biological changes are inevitable, because life in the sea is adapted to seawater exactly as it is.
My fantasy is for some improbable catalyst to be found that will enable the oxygen to be knocked off the carbon dioxide molecule with relatively little energy input, and the carbon atom to be added to a diamond crystal, all driven by a solar power plant in the desert. Carbon permanently sequestered, and diamonds worthless so lots of human suffering in Africa removed. But I digress …

Jem Cooper says: March 28th, 2010

Good to see this website is still alive. Calcium carbonate in the form of skeletal material from dead organisms accumulates continuously in shallow water sediments. In deeper water below roughly 4000 metres it all dissolves because of the effect of the pressure and the concentration of dissolved carbon dioxide. The rate of sedimentation roughly balances the arrival of dissolved calcium carbonate in river water, although sediment formation will decline as dissolved carbon dioxide from burning fossil fuel spreads through the ocean. Adding calcium oxide will help to balance the effect of that extra carbon dioxide.

The big problem for corals at the moment is the decline in carbonate ion concentration to about 78% of its preindustrial value. This makes it harder for them to grow their skeletons. If sufficient quicklime were added to absorb all the carbon dioxide from burning all the remaining fossil fuel (about thirteen times as much as has been burnt to date) ocean calcium concentration would rise by less than 2% of its current value, carbonate ion concentration and with it sedimentation rate would return to its preindustrial value and atmospheric CO2 concentration would be about where it is today. Job done. The process would happen naturally as rainwater dissolved limestone and washed calcium into the ocean but this would take hundreds of thousands of years.

Your fantasy process is just that. The energy required to knock the oxygen off the carbon dioxide is very high and precisely equal to that released when the carbon was originally burned. There are catalysts aplenty today that catalyse combustion and of course equally its reverse but they do not impact the energy released or consumed. That is why plants need sunlight.

Eduardo Vargas says: August 25th, 2011

I think that its possible for the idea to actually work, but I see the problem in the amount of energy this would take to use. had said that it would take about 10 billion barrels of oil to be able to do the scheme, and The United States consumes 7 billion per year. Its an enormous amount of energy, so where are we going to get that?

Jem Cooper says: September 1st, 2011

Carbon capture is always energy intensive. The energy to manufacture quicklime and capture the carbon dioxide produced at source would come from coal, and there is plenty of it still in the ground. To date we have used just one thirteenth of the available fossil fuel. Oil is much less plentiful and very much more expensive.

What is needed is not a solution for the bulk of today’s emissions. Carbon capture at source, nuclear, energy saving or wind are likely to be cheaper alternatives but some emissions to atmosphere from aircraft and ground vehicles on long journeys in remote areas will inevitably continue. It is for these sources that we need a technology to capture carbon from the atmosphere, and ocean quicklime addition is affordable technology that is already available.

m. plonsky says: December 14th, 2011

What about a slow-release calcium oxide pellet?

21st Century Tech Headlines for July 20, 2012 covering agriculture and food, bio-engineering, geo-engineering, new ocean remote sensing technology, and technology for maintaining fresh water supplies in Africa says: July 20th, 2012

[…] Of course there is an enormous cost. You can read about the idea at open source project site called Cquestrate. Cquestrate proposes heating limestone to very high temperatures to break it down into lime and CO2 […]

omer ibrahim says: October 27th, 2012

All these are really interesting solution for reducing emissions, my idea is to react the resulted CO2 with Ca(OH)2 to get the calcium carbonate again, which will be pure. What do you think about this?
Also i have other question, it might be a little bit far from this topic, but can any one tell me if there is an effect of using Solar heating in calcining on the lime properties?

Joao Jesus says: February 4th, 2013

I think CaO or Ca(OH)2 is potentially toxic (well one more than the other) so I would suggest some large scale basins for pilot tests or actual applications of this system in which seawater with limited wildlife is used for dissolve the lime and once the process is done release the seawater with a less toxic version of lime. Also, as quicklime dissolution is an exotermic reaction it would also induce temperature increases. This energy could be reuse in situ for the lime production process as it is dependent on heat not actual direct electricity.

HAARP frequency in our sky…BUSTED | mrmaxbliss says: May 13th, 2013

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Dr A. Cannara says: December 29th, 2014

CO2 “utilized either as the starting point for the production of fuels, or to enable biomass to be grown in arid environments, without the need for irrigation”

Not quite right. CO2 in air & seas now amounts to >1.5 trillion tons, with ~500 billion already dissolved in seas and >30 billion added each year by our emissions. the natural, dominant sequestration is by calcifying life forms in seas, which die and transport their calcite skeletal materials to seafloor sediment/limestone.

Even the 30 billion tons of emissions is far more CO2 than can be recycled into fuels. The amount of sequestered CO2 per year will need to be most or all of the >30 billion tons and must be permanently sequestered, as in basaltic formations (AAAS Science, 25 April 2014, p723). Extinctions of both sea food chains and the dominant C-sequestration system are on tap before 20650, if prompt, effective action isn’t taken. That action requires many tera-Watts of non-emitting power available for limestone process & lime distribution — an amount of power only available via nuclear.

Further, biomass growth isn’t water independent and depletes soil nutrients, apart from generating additional, dirty emissions from all harvest./transport/combustion activities.

This proposal needs more work. says: January 4th, 2015

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