CO2 Sequestration in Various Indus-trial Cement Products

The concentration of CO2 in the atmosphere has increased dramatically, which is causing irreversible change to global climate systems.  Carbon capture and storage is one course of action proposed to remove some of this excess CO2 and decrease the amount of new CO2 being emitted.  It is known that calcium will react with CO2 under certain conditions and create calcium carbonate<!–[if supportFields]> XE “calcium carbonate (CaCO3)” <![endif]–><!–[if supportFields]><![endif]–> (CaCO2), a stable compound that sequesters the carbon in a way that it is not reintroduced into the atmosphere.  Furthermore, there are several industrial, calcium-carrying materials that can participate in this reaction.  Previous research has shown that concrete can take up CO2 as carbonate while it is curing.  The incorporation of CaCO2 into the concrete makes the material stronger.  It also makes cement more compatible with wood materials for the production of products like wood-cement particleboard.  The carbonation also reduces shrinking by about 50% as cement sets and makes the material less permeable to water.  Currently, this practice is not used because the cost of producing CO2 is so high that it is not economically feasible.  However, it has been proposed that if recovered CO2 were used, then this option would become economically possible with the introduction of a carbon credits or carbon tax systems.  Monkman et al. (2010) compared different scenarios for using emitted CO2for this process and looked at the environmental and economic viability. —Anna Fiastro
Monkman, S., Shao, Y., 2010. Integration of carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> into curing process of precast concrete. Civil Engineering. DOI:10.1139/L09-140.

 The authors compared recovered CO2to untreated industrial flue gas emissions in their ability to carbonate 4 different cement products.  The recovered CO2 was imitated with highly concentrated and pressurized CO2.  For each exposure, a continuous supply was used, causing constant pressure and CO2 concentrations to mimic flue gas which is emitted at a pressure higher than atmospheric pressure. The cement product was closed in a chamber with the pressurized gas and allowed to take up the CO2.  After the designated period of time the chamber was emptied and refilled with flue gas.  This process was repeated about seven times, and each time the carbon uptake gradually slowed down as it reached saturation.  The amount of carbon taken up was quantified by the percent gain in mass of the cement.
Concrete masonry units (CMU) are one industrially produced product that was examined.  CMU were found to be the ideal candidate for carbon uptake because it is porous and already cured in a closed camber, making the addition of a gas easy.  Concrete paving stones were also looked at.  They are not subjected to any special curing scheme so they could easily be placed in a large sealed room filled with gas for the carbonation treatment.  Fiberglass mesh reinforced cement is a product that is cured with high pressure and moisture.  Because if this, a large surface area to volume ratio is necessary, which also lends itself to carbon uptake.  The last product examined in the study was cellulose<!–[if supportFields]>XE “cellulose” <![endif]–><!–[if supportFields]><![endif]–> fiberboard, used in place of asbestos cement.  The curing steps for this material can also easily be replaced by carbonation curing, giving the benefit of hydration of the material and carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  Both the fiberglass mesh cement and cellulose fiberboard benefit from a lowered pH, protecting the material from alkali corrosion.
All four of these materials would benefit in strength and durability from carbonation, and their curing processes could easily be replaced or supplemented by carbonation curing.  In all cases the uptake from recovered CO2 was greater than uptake from flue gas. 
It is also important to compare the energy and CO2 penalties for recovering, compressing, and transporting the CO2 in order for it to be used.  When this is taken into consideration, recovered CO2 is still the most viable option, because it is already at high concentrations.  The compression and transportation of flue gas makes it only feasible if the curing process occurs on site.  The transportation associated with recovered CO2 can also be compared to other capture and storage methods, such as geological storage, which would result in equal or more transportation emissions.
Part of the analysis of processing emissions is the comparison of carbonation curing with steam and autoclave curing, the methods predominantly used in the industry.  The emissions from carbonation curing are less than one tenth of those associated with steaming and autoclaving.  This method is also attractive if one takes into account the possible trading value of carbon and improved technologies reducing energy use in production phases.
One last analysis was done looking at the carbon uptake of ladle slag<!–[if supportFields]> XE “slag” <![endif]–><!–[if supportFields]><![endif]–> fines as a replacement for sand.  This was done using a different CO2exposure process than the other materials.  The particulates were exposed to gas made up of 50% CO2 at atmospheric pressure.  This was meant to replicate flue gas without the compression step that is so energy expensive.  The material was found to have a modest carbon uptake of about 10% after almost 60 days.  This is not thought to be the best opportunity for carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> but other calcium-rich slags may serve this goal more affectively.

Possible Negative Implications of Ocean Urea Fertilization

Since the industrial revolution, there has been an ever-increasing concentration of CO2in the atmosphere contributing to global climate change.  Ocean fertilization<!–[if supportFields]> XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–> is one proposed method of carbon capture and storage<!–[if supportFields]> XE “carbon capture and storage (CCS)”<![endif]–><!–[if supportFields]><![endif]–>; it is the use of fertilizers to stimulating the growth of phytoplankton<!–[if supportFields]> XE “phytoplankton” <![endif]–><!–[if supportFields]><![endif]–> species that take up CO2 in their growth.  One fertilizer<!–[if supportFields]> XE “fertilizer” <![endif]–><!–[if supportFields]><![endif]–> being proposed is urea, a nitrogen<!–[if supportFields]> XE “nitrogen” <![endif]–><!–[if supportFields]><![endif]–> rich organic compound.  Unlike nitrogen fertilization, research of the effectiveness of urea as an ocean fertilizer is only being conducted by one laboratory at the University of Sydney, which has connections with Ocean Nourishment Corporation (ONC)<!–[if supportFields]> XE “Ocean Nourishment Corporation (ONC)” <![endif]–><!–[if supportFields]><![endif]–>, a company that has the patent on the procedure.  The environmental and social aspects of this procedure must be fully examined to determine if it a safe and effective solution for carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–> before it is implemented on a large scale.  Mayo-Ramsay (2010) discusses the process of urea fertilization, and its ability to reduce atmospheric levels of carbon and stimulate fisheries.  She also examines its possible effects on the Sulu Sea, the leading site being considered. —Anna Fiastro
Mayo-Ramsay, J., 2010. Environmental, legal and social implications of ocean urea fertilization<!–[if supportFields]> XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–>: Sulu sea example. Marine Policy. 34, 831835.

Ocean urea fertilization<!–[if supportFields]>XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–> utilizes a nutrient solution produced by mixing urea with other limiting nutrients.  This nutrient solution is then put in the ocean where it increases the abundance of phytoplankton<!–[if supportFields]>XE “phytoplankton” <![endif]–><!–[if supportFields]><![endif]–>, and the resultant uptake of carbon from the atmosphere.  This stimulation at the lowest trophic<!–[if supportFields]>XE “trophic”<![endif]–><!–[if supportFields]><![endif]–> level is thought to trickle up the food chain and increase marine productivity of larger fish.  The two benefits that are outlined are the sequestration<!–[if supportFields]>XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–> of carbon and the increase in fish populations, which could help in the face of a global food shortage. 
Professor Ian Jones is the head of the Ocean Technology Group at the University of Sydney, the only laboratory conducting research on urea fertilization<!–[if supportFields]> XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–>.  He also has interests in the Ocean Nourishment Corporation, an Australian commercial organization that has patented its urea fertilization technology.  While the company claims to have conducted research on its technique and possible implications, no peer reviewed scientific articles have been published.  The company did not consult the local governments or communities that would be affected by this experimentation.
Other scientific discussions and studies being conducted by independent groups have identified various possible dangers related to ocean fertilization<!–[if supportFields]> XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–>.  Added fertilizer<!–[if supportFields]>XE “fertilizer” <![endif]–><!–[if supportFields]><![endif]–> can lead to the creation of hypoxic zones (areas void of oxygen) as well as the release of nitrous oxide<!–[if supportFields]> XE “nitrous oxide (N2O)” <![endif]–><!–[if supportFields]><![endif]–> (N2O).  This increase in nutrients can lead to an imbalance in the different species of phytoplankton<!–[if supportFields]> XE “phytoplankton” <![endif]–><!–[if supportFields]><![endif]–> and ecosystem composition.  There is also a question of whether or not such fertilization actually leads to carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  While the phytoplankton blooms do take up CO2, the carbon must not be released back into the atmosphere in order for it to be an effective solution for climate change.  In this case, the dead material constructed from the carbon must sink to the bottom of the ocean, but evidence shows that the phytoplankton stay on or near the surface creating a scum. 
The proposed urea fertilization<!–[if supportFields]>XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–> plant would pump urea into the Sulu Sea southeast of Asia.  This site was selected because it is a fairly enclosed body of water that lacks nutrients but has sufficient phosphorous.  While this might seem like a good location, the limited circulation can intensify the possibility of anoxic conditions with increased nutrients. 
The other proposed benefit of the program is increased marine productivity, which would supposedly stimulate the local fisheries.  Currently there is a vibrant aquaculture<!–[if supportFields]> XE “aquaculture” <![endif]–><!–[if supportFields]><![endif]–> industry in the region and long-term production of fish through this method has not been proven.  Even if there were increased productivity, the management of this fishery would become very complicated.  The proposed site in the Sulu Sea is bordered by a number of States.  The Ocean Nourishment Corporation has proposed a specific fishing license that would be necessary to fish in the waters affected by their plant, but would be nearly impossible to determine which fish were wild and which were grown under the influence of the fertilization<!–[if supportFields]> XE “fertilization” <![endif]–><!–[if supportFields]><![endif]–> conditions.  Such a license would also be detrimental to the local fisher<!–[if supportFields]> XE “fisher” <![endif]–><!–[if supportFields]><![endif]–>-people who rely on the fish for their survival, presenting a serious legal barrier to the viability and completion of this project.

Another legal concern is the distribution of the carbon credits obtained through the carbon sequestration<!–[if supportFields]> XE “carbon sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  Currently the International Organization for Standardization is coordinating a system to validate and verify greenhouse gas accounting.  The benefits of the program would need to be quantified and distributed among the States and organizations participating in the project, but the number of States involved makes this process difficult to agree upon, implement, and regulate. 

Sequestration of New CO2 Emissions by Reacting with Seawater

Human activity has caused the CO2 levels in the atmosphere to increase to dangerous levels, resulting in changes in the earth’s climate.  Everyday new CO2 emissions are being released from various sources and adding to this problem.  Carbon intensive industrial plants, such as coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–>-fired power plants, contribute a large portion of these waste gas emissions. Wang et al. (2011) have investigated the use of magnesium and calcium ions to react with the emitted CO2 to form a carbonate precipitate.  The carbonate is a very stable substance that sequesters the carbon and keeps it from separating and mixing into the atmosphere.  The authors propose the use of seawater as the source for the magnesium and calcium ions, particularly waste seawater from desalination<!–[if supportFields]> XE “desalination” <![endif]–><!–[if supportFields]><![endif]–> plants with high ion concentrations.  They determined the optimal conditions to push this reaction to form the most carbonate precipitant. —Anna Fiastro
Wang, W., Hu, M., Ma, C. 2011. Possibility for CO2 sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–> using seawater. Bioinformatics and Biomedical Engineering 4, 14.

Wang et al. focused on the mixing of salt water with the CO2 emissions from coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–> power plants.  They used various equations to calculate the possible carbonate precipitation under different conditions and carbon emissions.  They found that the pressure of the carbon containing gas and the acidity of the salt solution were the two driving factors of the reaction, and determined the optimal partial pressure and pH range.
For this reaction to happen the CO2 from the gas must be absorbed into the liquid.  By increasing the pressure of the gas, more CO2 passes into the liquid and is available to form carbonate ions. The atmospheric pressure allows the ocean to take up CO2 from the atmosphere naturally, but this is a slow process.  Increasing the pressure to more than 1 atmosphere speeds up the formation of carbonate.  Emissions from most industrial plants are in a gas form that has a partial pressure several times higher than that of the atmosphere.  Therefore, the mixing of this gas with seawater should accelerate the process.
Wang et al. established that an enhanced alkaline solution would also lead to increased carbonate precipitation.  Increased pH drives the buffer equilibrium from CO2 towards the formation of carbonate ions (CO32-).  These ions then react to form the carbonate, which is precipitated out, sequestering the carbon in a stable condition.  The more basic the solution, the more carbonate ions there are to form carbonate.  There is however a threshold for this trend, where the pH is too high and unwanted precipitates are formed. Seawater does not have the optimal pH to push this reaction; however increasing its pH is a very difficult. The authors propose several ways to increase pH, including electrolytically, but with the technology available today, they are all expensive processes.
Pressure and pH cause more carbonate ions to be present to react with other positive ions to form the carbonate solids.  The author’s analysis of the various cations in seawater found that magnesium and calcium are abundant enough and strong enough cations to precipitate carbonate anions.  The condensed seawater that comes from desalination<!–[if supportFields]> XE “desalination” <![endif]–><!–[if supportFields]><![endif]–> plants as well as underground brine offer high concentrations of these ions to react with the carbonate ions.
Finally, Wang et al. applied these ideas to an existing coal<!–[if supportFields]> XE “coal” <![endif]–><!–[if supportFields]><![endif]–>-fired power plant.  When the pressure of the gas and pH of the solution where known, the amount of precipitate could be calculated and the amount of carbon sequestered could be predicted.  The addition of alkaline seawater to emissions seems to be a promising method of carbon capture and storage<!–[if supportFields]> XE “carbon capture and storage (CCS)” <![endif]–><!–[if supportFields]><![endif]–> in the form of carbonate precipitate.

Long-term Effectiveness of Dif-ferent Types of CO2 Sequestra-tion

Increasing levels of CO2 in the earth’s atmosphere are causing changes to the climate on a global scale.  Methods have been proposed to reduce the amount of carbon in the atmosphere as well as to decrease the amount of new carbon emissions being released.  Carbon capture and storage has become a prominent proposal for collecting CO2 from industrial outputs and sequestering them in various places.  Many methods and locations have been proposed for carbon storage.  Shaffer (2010) has researched and predicted the long-term effectiveness and consequences of different storage techniques, including deep ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, onshore geological storage, and deep-ocean sediment storage.  He compared these to a “business-as usual” emissions model, based on projections if no changes are made to current practices, and to a desirable future emissions model, which is the ‘best-case’ scenario for avoiding strong global warming.  All the projections are drawn out to 50,000 A.D.  Shaffer found that these methods offer short term solutions, because CO2 is leaked and reintroduced into the atmosphere causing a delayed global warming effect.  He concludes that the best way to free ourselves and future generations of this climate burden is to dramatically reduce emissions now.—Anna Fiastro
Shaffer, G. 2010. Long-term effectiveness and consequences of carbon dioxide sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>. Nature Geoscience. DOI:10.1030/NGEO0896.

Shaffer used the IPCC<!–[if supportFields]> XE “Intergovernmental Panel on Climate Change (IPCC)” <![endif]–><!–[if supportFields]><![endif]–> SRES model for the ‘business–as-usual’ and ‘best-case’ scenarios, and the Danish Center for Earth System Science (DCESS) model to make the long-term projections for the onshore and offshore scenarios. He compares the partial pressure of atmospheric CO2, the geologically stored CO2, the mean atmosphere and ocean warming, ocean carbon inventory change, and the ‘dead zone’ volume fraction of each method for the 50,000-year time scale.  The change in pH and change in CO2 was also predicted at the oceans surface and at 3,000 meters depth, for each scenario. 
The ‘business-as-usual’ scenario had the highest CO2 partial pressure and the most atmospheric and ocean warming for all that scenarios and the peaks in all three of these categories were the earliest on the time scale.  This is to be expected because it does not involve any attempt to reduce the CO2 emissions or their effects.  This scenario also resulted in the highest fraction of global ocean volume to be considered a dead zone, meaning that there would be very little oxygen dissolved in the water to support life.  “Business-as-usual” had a dramatic effect in the amount of carbon in the surface layers of the ocean, but did not have the greatest overall change in the amount of carbon in the ocean.  In this category it was overshadowed by the deep-ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>.  This analysis shows that some action should be taken in the face of increasing atmospheric carbon levels. 
In deep-ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, CO2 is pumped into the cold, lower layers of the ocean that do not readily mix with the upper layers.  In the long term this method for storing carbon has similar effects as the “business-as-usual” on atmospheric partial pressure of CO2, atmospheric and oceanic warming, and the fraction of the ocean that is a “dead zone,” but not until 2,000 years later.  Then the ocean becomes mixed sufficiently to release the sequestered CO2 to the atmosphere.  Since in this method the CO2 is directly introduced into the water, it does increase the amount of carbon in the ocean more dramatically than any of the other methods.
Another approach analyzed is onshore geological storage, where emissions are injected into geological formations deep underground.  With this approach, there is a possibility of CO2 leaking from the geological container and being introduced to the atmosphere.  Therefore, this method was analyzed using three different leakage scenarios; rapidly, moderately, and weakly leaking projections.  The rapidly leaking geological formation scenario had effects similar to the deep-ocean and the ocean sediment methods with severe affects on all the measured factors, but the effects where delayed when compared to current practices.  The moderately leaking scenario was about half as severe as the rapidly leaking scenario and the peak was delayed by about 5,000 years after the ‘business-as-usual.’   The slowly leaking scenario had very little effect at all and was similar to the ‘best-case’ scenario, at least 50,000 years out when it was starting to show the same trends as the other scenarios, with rising effects in ocean carbon inventory and atmospheric and ocean warming.  This is to be expected because the slow leakage would cause a more drawn out and subtle effect on the factors being examined, but an effect none the less.
The last method analyzed is to inject CO2 into deep offshore ocean sediments.  This projection was done assuming that the sequestered carbon would ‘rapidly’ leak from the rock confines.  Since this is an offshore injection site, it will leak into the deep ocean layers.  Thus, the projections are similar to those of deep ocean sequestration<!–[if supportFields]> XE “sequestration” <![endif]–><!–[if supportFields]><![endif]–>, but delayed 1,000 years by the CO2 leaking out of the rock.

Shaffer concludes that while all these methods seem to minimize the effects of CO2 emissions, the long-term effects are still present.  He suggest that the best solution is to stop new emissions as soon as possible instead of trying to hide them away, and have them come back to cause trouble for future generations.

The Effects of Injecting CO2 into Deep Bethypelagic Layers of the Ocean

In the face of increasing CO2 levels in the atmosphere one approach to reducing new CO2 emissions is carbon capture and storage.  Yamada et al. (2010) examine the technique of dissolution; injecting CO2 into deep layers of the ocean.  The limited mixing of these deep waters would prevent the CO2 from entering the atmosphere for a long time, but the CO2 could affect the prokaryotic populations at these depths and their associated nutrient cycles.  The research looked at the effects of increased CO2 on these populations by capturing samples of them in water samples from deep in the Pacific Ocean and conducting laboratory experiments on them, increasing CO2 levels and evaluating the effects.—Anna Fiastro
Yamada, N., Tsurushima, N., Suzumura, P., 2010. Effects of Seawater Acidification by Ocean CO2 Sequestration on Bathypelgic Prokaryote Activities. Journal of Oceanography. Vol 66, p 571-580.

The plan for dissolution is to inject CO2 into the benthypelagic zone, which ranges from 1000 to 3000 meters from the surface.  This is an important area for the regeneration of nutrients and organic material.  The layers of the ocean are separated by temperature and salinity gradients that prevent mixing. Due to limited mixing of the layers of the ocean it is thought that the CO2 would not move up and not be introduced into the atmosphere.  The CO2 would dissolve into the surrounding water and remain at depth, causing a decrease in the pH, also known as acidification, but only locally.  It is important to look at the effects of these elevated CO2 levels on the systems that operate in these layers, specifically the prokaryotes who are responsible for these nutrient cycles.
          Yamada et al. took water samples from two different locations in western North Pacific at 2000 meters deep, which were used in experiments within 10 days of sampling.  CO2 injection conditions were simulated by bubbling air containing different concentrations of CO2 though the tanks containing the samples.  The pH, total cell count, and heterotrophic prokaryotic production rates were monitored in each sample.  Although there was variation between the sites, thought to be due to seasonal differences, clear results were obtained.  The bubbling of CO2 increased the acidity of the water (decreased the pH).  The total cell counts remained relatively constant independent of pH, but the heterotrophic prokaryotic production rates decreased with increasing acidity.  Another way to say this is that with more CO2 in the water, productivity of the organisms living in it went down. 
It seems counter-intuitive that total cell count would remain the same while productivity went down.  In order to further examine this, the researchers looked at the direct viable count, or the number of thriving prokaryotic cells capable of growth.  This was shown to decrease with acidification, explaining the decreased productivity rates.
Another trial was run in which acidification was simulated by adding a chemical buffer.  This showed similar results to the CO2 bubbling method.  As pH decreased and acidity increased, prokaryotic growth and production were lowered.
In these experiments, acidification suppressed bacterial activity more than Archaea activity.  The significance of this is not fully understood, and further research is necessary to look at the life histories of different types of Archaea to better understand their reaction to changing pH levels.

Sequestration of CO2 in Basalt Geological Formations Along the Eastern Seaboard of the United States

Carbon capture and storage has been proposed as an important component to a well rounded plan to control increasing carbon dioxide levels in the earth’s atmosphere.  One method for sequestering CO2 is to pump new emissions into geological formations.  Previous research has shown basalt and ultramafic rock reservoirs to be good, secure, long term locations for the sequestration of CO2.  Goldberg et al. (2010) examined the potential of various reservoir sites in the Central Atlantic Magmatic Province (CAMP) basalt flows to be sequestration sites for large cities along the eastern seaboard of the United States.—Anna Fiastro
Goldberg, D., Kent, D., Olsen, P., 2010. Potential on-shore and off-shore reservoirs for CO2 sequestration in Central Atlantic magmatic province basalts. Proceedings of the National Academy of Science 107, 1327.doi:10.1073/pnas.0913721107.

          The Central Atlantic Magmatic Province (CAMP) lies on and off shore along the eastern coast of North America.  CAMP consists of numerous basins of thick continental sediments with veins of basalt running through them.  These basins were created during the Triassic and Jurassic time periods.  Since these events, other seismic activity and interactions with water and the atmosphere have caused some of these rock formations to erode, while the remainders have become stratified with varying thickness and composition over a large area.  This stratification has lead to ideal conditions for CO2 injection and sequestration.
          What has occurred is that layers of very thick and dense basalt have surrounded areas of less dense and porous basalt.  The porous basalt allows space for a chemical reaction to occur between the minerals of the basalt and the injecting CO2 creating a mineral carbonate that fills in the cracks.  The dense basalt layers seal the pumped CO2 and the carbonate product in the basin so that it is harder for it to be reintroduced into the environment and atmosphere.
          These authors speculate that these types of layered formations can be found in the Orange Mountain basalt, the Newark Rift Basin, the Long Island Rift Basins, and the South Georgia Rift Basin.  This is based on sampling data, density and porosity profiles, computer modeling, and scientific speculation.  These sites are close to major metropolitan areas on the east coast of the United States, allowing them to work efficiently as storage locations for areas of high industrial CO2 output.  The speculated size of the reservoirs also offers the potential to store massive amounts of CO2.  For example, estimates show that one basin could contain the equivalent emissions from 3 or more coal-fired power plants for up to 40 years. 
Further study is necessary to confirm the existence of these basins, and demonstrate their suitability to act as sequestration locations.  Studies would include high-resolution survey mapping, followed by drilling in and around locations.  Pilot injection projects would then be conducted and monitored to determine the safety and effectiveness of this form of capture and storage.  Goldberg et al. also suggested that research should first be conducted at on-shore sites as they are more accessible and cost effective, and then offshore sites can be explored with the increased technology and knowledge.

Sequestration of CO2 in Geological Formations as Carbonate Minerals.

Atmospheric carbon dioxide concentrations have been steadily increasing over the past century causing detrimental effects on the earth’s climate.  In addition to efforts to decreased future carbon emissions, the capture and storage of current CO2 in the atmosphere is an important component of a long-term solution to for reducing CO2 concentrations.  One method proposed for this is geological CO2 storage.  This is a process in which CO2 emissions are pumped into geological formations instead of into the earth’s atmosphere.  Since the CO2 being inserted in to the rock is buoyant, when compared to the rock and surrounding water, there are different trapping mechanisms to insure that the CO2 remains at depth and does not resurface to be released into the air.  The focus of this paper by Matter and Kelemen (2009) is “mineral tapping” in which dissolved CO2 reacts with water and the minerals of the surrounding rock to form solid carbonate that will remain in place.  This is a long-term storage solution for large quantities of CO2.  The success of this solution, however, depends on the type of physical and chemical properties of the location chosen for injection.—Anna Fiastro
Matter, J., Kelemen, P., 2009. Permanent storage of carbon dioxide in geological reservoirs by mineral carbonation. Nature geoscience. doi:10.1038/NGEO683.
The emissions are pumped to depths of over 800 meters where the combination of temperature, pressure, and salinity in addition to the pH of the location induced a fluid-rock reaction that causes carbonate mineral formation.  Early studies examined deep aquifers in sedimentary rock because of the porous nature of the rock.  It was thought that space was a necessary characteristic of the host rock because it offered a place to deposit the carbonate mineral product.  Sedimentary rock includes sandstone, siltstone, shale, and limestone, however these types of rock have very low mineral trapping potential.  This is seen in prediction models run in various labs, and in field observations of natural CO2 reservoirs leeching into rock.
          The field of research then looked towards aquifers containing ‘basic’ silicate minerals, such as olivine, serpentine, pyroxenes, plagioclase, and basaltic glass. It was found that silicate minerals buffer the pH in these reactions making them essential for enhancing mineral storage. It has been shown in laboratory experiments and in natural analogues that these types of rock react rapidly to form carbonate minerals.  These types of rock are also commonly found all around the world and on every continent.  This means that their capacity for CO2 storage in carbonate is enormous.
The original concern with mineral trapping was the need for space.  The reactions are often self-limiting because they fill in empty space and can create boundaries between the unreacted CO2 and fluid.  As was mentioned earlier, this was the advantage of sedimentary rock originally being examined.  The porous nature of the rock is important to ensure ample room for product creation. It was thought that optimal rock containing silicate minerals would not be porous enough to have a continued reaction and convert all of the CO2 to carbonate.  As a solution to this, it is hypothesized that the crystallization can fracture the rock to increase permeability.  This has been proven to occur in both laboratory simulations as well as naturally occurring systems.  The fracturing that occurs creates more space for the carbonate product to be deposited and allowed the reactants to continually come in contact with each other forming more carbonate.
Another aspect that makes this process a favorable solution to CO2 capture is the self-heating cycle that occurs.  Heat is given off from the initial reaction and remains to speed up the continued reaction of more and more CO2, increasing the overall reaction rate.  With continued reactions taking place, the elevated temperature is maintained and so is the speedy reaction rate.  This results in more and more CO2 being sequestered.
The combination of silicate minerals, fracturing and excess heat allow for large quantities of carbon dioxide to be captured and deposited in underground aquifers as carbonate minerals.  This is a solution to increased CO2 levels that is being examined further.

Effects of Iron Fertilization on Diatom Populations and Domoic Acid Concentrations

Iron fertilization has been proposed as a solution to increased levels of CO2 in the atmosphere and the resulting acidification of the world’s oceans.  Iron fertilization is a process in which iron is added to areas of open ocean to induce phytoplankton blooms; the species of phytoplankton targeted sequester CO2 in their cells removing it from the atmosphere and upper levels of the oceans.  The idea I that as these cells die they will sink to the bottom of the ocean with the acquired carbon where it will remain.  It is important, however, to weigh the benefits of this procedure against the possible consequences.  Silver et al. (2010) have shown that iron fertilization leads to increased biomass of diatom species from the genus Pseudo-nitzschia, which are known to produce the neurotoxin domoic acid (DA).  This increase is directly correlated with increased levels of DA in the environment.  This neurotoxin has been shown to have negative effects in both coastal and oceanic ecosystems, as well as at depth below fertilization sites; and the extent of this increases still is not fully understood.—Anna Fiastro

Silver, M., Bargu, S., Coale, S., Benitez-Nelson, C., Garcia, A., Roberts, K., Sekula-Wood, E., Bruland, K., Coale, K.,2010.Toxic diatoms and domoic acid in natural and iron enriched waters of the oceanic Pacific. Proceedings of the National Academy of Science 107, 20762.doi:10.1073/pnas.1006968107.

Silver and colleagues surveyed 34 stations ranging from the Pacific subarctic to the Southern Ocean, some of which were historic iron fertilization sites.  They collected and analyzed near surface water samples and sediment samples.  They quantified and identified eleven Pseudo-nitzschia species from these samples and measured DA concentrations in the cells and water of each sample.
A correlation was found between increased Pseudo-nitzschia cell abundance and increased DA concentrations.  Eleven species from the genus were identified in the samples, some containing just one species and some up to 4 different species.  Due to the method of data collection toxin levels could not be assigned to specific species.  Variability in toxin levels was attributed to different combinations of species as well as between variability among individuals or cells within a species.  This variability is due to varying physical and chemical conditions as well as different strains within the species.  This, however, does not affect the clear correlation between cell abundance and DA toxin levels.
It was also found that increased levels of DA toxin and Pseudo-nitzschia abundance was linked to areas of historic iron enrichment experimentation.  While it has not yet been shown that these elevated toxin levels impact higher trophic levels in oceanic ecosystems, as seen in coastal regions, it has been proven that DA has reached levels that pose a threat to the oceanic ecosystems.
The data from this study also suggest that DA neurotoxins are delivered to deeper depths in the intact cells of these Pseudo-nitzschia species and at higher rates with iron fertilization.  In areas where prior studies using iron fertilization took place, intact diatom cells containing DA were found in sediment samples that correlated with blooms occurring after fertilization.