Carbon sequestration

Carbon sequestration or carbon dioxide removal (CDR) is the long-term removal, capture or sequestration of carbon dioxide from the atmosphere to slow or reverse atmospheric CO2 pollution and to mitigate or reverse global warming.

Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land use and agricultural practices, such as converting crop and livestock grazing land into land for non-crop fast growing plants. Artificial processes have been devised to produce similar effects, including large-scale, artificial capture and sequestration of industrially produced using subsurface saline

aquifer

s, reservoirs,

ocean water

, aging

oil field

s, or other carbon sinks, bio-energy with carbon capture and storage,

biochar

, ocean fertilization, enhanced weathering, and direct air capture when combined with storage.

The likely need for CDR has been publicly expressed by a range of individuals and organizations involved with climate change issues, including IPCC chief Rajendra Pachauri, the UNFCCC executive secretary Christiana Figueres, and the World Watch Institute. Institutions with major programs focusing on CDR include the Lenfest Center for Sustainable Energy at the Earth Institute, Columbia University, and the Climate Decision Making Center, an international collaboration operated out of Carnegie-Mellon University's Department of Engineering and Public Policy.

Description

Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric

carbon dioxide

() and may refer specifically to:
* "The process of removing carbon from the atmosphere and depositing it in a reservoir." When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering.
*

Carbon capture and storage

, where carbon dioxide is removed from flue gases (e.g., at

power station

s) before being stored in underground reservoirs.
* Natural biogeochemical cycling of

carbon

between the

atmosphere

and reservoirs, such as by chemical weathering of rocks.

Carbon dioxide may be captured as a pure by-product in processes related to petroleum refining or from flue gases from power generation. sequestration includes the storage part of carbon capture and storage, which refers to large-scale, artificial capture and sequestration of industrially produced using subsurface saline

aquifers

, reservoirs,

ocean water

, aging

oil field

s, or other carbon sinks.

Carbon sequestration describes long-term storage of

carbon dioxide

or other forms of

carbon

to either mitigate or defer global warming and avoid dangerous climate change. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels and more so caused by industrial livestock production.

Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes. Some artificial sequestration techniques exploit these natural processes, while some use entirely artificial processes.

There are three ways that this sequestration can be carried out; post-combustion capture, pre-combustion capture, and oxy-combustion. A wide variety of separation techniques are being pursued, including gas phase separation, absorption into a liquid, and adsorption on a solid, as well as hybrid processes, such as adsorption/membrane systems. These above processes basically capture carbon emitting from power plants, factories, fuel burning industries, and new generation livestock production facilities as they transition into restorative farming techniques, which is used by organizations as they look to reduce carbon emissions from thei
operations.

Biological processes

Biosequestration

Biosequestration is the capture and storage of the atmospheric greenhouse gas

carbon dioxide

by continual or enhanced biological processes. This form of

carbon sequestration

occurs through increased rates of

photosynthesis

via land-use practices such as reforestation,

sustainable

forest management, and genetic engineering.

Carbon sequestration through biological processes affects the global

carbon cycle

. Examples include major climatic fluctuations, such as the Azolla event, which created the current

Arctic

climate. Such processes created fossil fuels, as well as clathrate and

limestone

. By manipulating such processes, geoengineers seek to enhance sequestration.

Peatland

Peat bogs act as a sink for carbon due to the accumulation of partially decayed biomass that would otherwise continue to decay completely. There is a variance on how much the peatlands act as a carbon sink or carbon source that can be linked to varying climates in different areas of the world and different times of the year. By creating new bogs, or enhancing existing ones, the amount of carbon that is sequestered by bogs would increase.

Forestry

Afforestation is the establishment of a forest in an area where there was no previous tree cover. Reforestation is the replanting of trees on marginal crop and

pasture

lands to incorporate carbon from atmospheric into

biomass

.
For this carbon sequestration process to succeed the carbon must not return to the atmosphere from mass burning or rotting when the trees die. To this end, land allotted to the trees must not be converted to other uses and management of the frequency of disturbances might be necessary in order to avoid extreme events. Alternatively, the wood from them must itself be sequestered, e.g., via

biochar

, bio-energy with carbon storage ( BECS), landfill or 'stored' by use in e.g., construction. Short of growth in perpetuity, however, reforestation with long-lived trees (>100 years) will sequester carbon for substantial period and be released gradually, minimizing carbon's climate impact during the 21st century. Earth offers enough room to plant an additional 1.2 trillion trees. Planting and protecting them would offset some 10 years of CO₂ emissions and sequester 205 billion tons of carbon. This approach is supported by the Trillion Tree Campaign. Restoring all degraded forests world would capture about 205 billion tons of carbon in total (which is about 2/3rd of all carbon emissions.

In a paper published in the journal ''Nature Sustainability,'' researchers studied the net effect of continuing to build according to current practices versus increasing the amount of wood products. They concluded that if during the next 30 years new construction utilized 90% wood products that 700 million tons of carbon would be sequestered. This is the equivalent of about 7 days worth of global emissions in 2019.

Urban forestry

Urban forestry increases the amount of carbon taken up in cities by adding new tree sites and the sequestration of carbon occurs over the lifetime of the tree. It is generally practiced and maintained on smaller scales, like in cities. The results of urban forestry can have different results depending on the type of vegetation that is being used, so it can function as a sink but can also function as a source of emissions. Along with sequestration by the plants which is difficult to measure but seems to have little effect on the overall amount of carbon dioxide that is uptaken, the vegetation can have indirect effects on carbon by reducing need for energy consumption.

Wetland restoration

Wetland soil is an important carbon sink; 14.5% of the world's soil carbon is found in wetlands, while only 6% of the world's land is composed of wetlands.

Agriculture

Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When a soil is converted from natural land or semi natural land, such as forests, woodlands, grasslands, steppes and savannas, the SOC content in the soil reduces by about 30–40%. This loss is due to the removal of plant material containing carbon, in terms of harvests. When the land use changes, the carbon in the soil will either increase or decrease, this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated climate . The decreasing of SOC content can be counteracted by increasing the carbon input, this can be done with several strategies, e.g. leave harvest residues on the field, use manure as fertiliser or include perennial crops in the rotation. Perennial crops have larger below ground biomass fraction, which increases the SOC content. Globally, soils are estimated to contain >8,580 gigatons of organic carbon, about ten times the amount in the atmosphere and much more than in vegetation.

Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of 2010 carbon dioxide emissions annually. (See No-till). Restoration of organic farming and earthworms may entirely offset CO2 annual carbon excess of 4 Gt per year and drawdown the residual atmospheric excess. (See

Compost

).

Carbon emission reduction methods in agriculture can be grouped into two categories: reducing and/or displacing emissions and enhancing carbon removal. Some of these reductions involve increasing the efficiency of farm operations (e.g. more fuel-efficient equipment) while some involve interruptions in the natural carbon cycle. Also, some effective techniques (such as the elimination of stubble burning) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning).

Carbon farming

Carbon farming is a name for a variety of agricultural methods aimed at sequestering atmospheric carbon into the soil and in crop roots, wood and leaves. Increasing soil's carbon content can aid plant growth, increase soil organic matter (improving agricultural yield), improve soil water retention capacity and reduce fertilizer use (and the accompanying emissions of greenhouse gas nitrous oxide (N2O).As of 2016, variants of carbon farming reached hundreds of millions of hectares globally, of the nearly 5 billion hectares (1.2×1010 acres) of world farmland. Soils can contain up to five per cent carbon by weight, including decomposing plant and animal matter and biochar.

Potential sequestration alternatives to carbon farming include scrubbing CO2 from the air with machines (direct air capture); fertilizing the oceans to prompt algal blooms that after death carry carbon to the sea bottom; storing the carbon dioxide emitted by electricity generation; and crushing and spreading types of rock such as basalt that absorb atmospheric carbon. Land management techniques that can be combined with farming include planting/restoring forests, burying biochar produced by anaerobically converted biomass and restoring wetlands. (Coal beds are the remains of marshes and peatlands.)

Bamboo farming

Although a bamboo forest stores less total carbon than a mature forest of trees, a bamboo plantation sequesters carbon at a much faster rate than a mature forest or a tree plantation. Therefore the farming of bamboo timber may have significant carbon sequestration potential.

Deep soil

Soils hold four times the amount of carbon stored in the atmosphere. About half of this is found deep within soils. About 90% of this deep soil C is stabilized by mineral-organic associations.

Reducing emissions

Increasing yields and efficiency generally reduces emissions as well, since more food results from the same or less effort. Techniques include more accurate use of

fertilizer

s, less soil disturbance, better

irrigation

, and crop strains bred for locally beneficial traits and increased yields.

Replacing more energy intensive farming operations can also reduce emissions. Reduced or no-till farming requires less machine use and burns correspondingly less fuel per acre. However, no-till usually increases use of weed-control chemicals and the residue now left on the soil surface is more likely to release its to the atmosphere as it decays, reducing the net carbon reduction.

In practice, most farming operations that incorporate post-harvest crop residues, wastes and byproducts back into the soil provide a carbon storage benefit. This is particularly the case for practices such as field burning of stubble – rather than releasing almost all of the stored to the atmosphere, tillage incorporates the biomass back into the soil.

Enhancing carbon removal

All crops absorb during growth and release it after harvest. The goal of agricultural carbon removal is to use the crop and its relation to the carbon cycle to permanently sequester carbon within the soil. This is done by selecting farming methods that return biomass to the soil and enhance the conditions in which the carbon within the plants will be reduced to its elemental nature and stored in a stable state. Methods for accomplishing this include:
* Use cover crops such as grasses and weeds as temporary cover between planting seasons
* Concentrate livestock in small paddocks for days at a time so they graze lightly but evenly. This encourages roots to grow deeper into the soil. Stock also till the soil with their hooves, grinding old grass and manures into the soil.
* Cover bare paddocks with hay or dead vegetation. This protects soil from the sun and allows the soil to hold more water and be more attractive to carbon-capturing microbes.
* Restore degraded land, which slows carbon release while returning the land to agriculture or other use.

Agricultural sequestration practices may have positive effects on

soil

, air, and water quality, be beneficial to

wildlife

, and expand food production. On degraded croplands, an increase of 1 ton of soil carbon pool may increase crop yield by 20 to 40 kilograms per hectare of

wheat

, 10 to 20 kg/ ha for maize, and 0.5 to 1 kg/ha for cowpeas.

The effects of soil sequestration can be reversed. If the soil is disrupted or tillage practices are abandoned, the soil becomes a net source of greenhouse gases. Typically after 15 to 30 years of sequestration, soil becomes saturated and ceases to absorb carbon. This implies that there is a global limit to the amount of carbon that soil can hold.

Many factors affect the costs of carbon sequestration including soil quality, transaction costs and various externalities such as leakage and unforeseen environmental damage. Because reduction of atmospheric is a long-term concern, farmers can be reluctant to adopt more expensive agricultural techniques when there is not a clear crop, soil, or economic benefit. Governments such as Australia and New Zealand are considering allowing farmers to sell carbon credits once they document that they have sufficiently increased soil carbon content.

Ocean-related

Iron fertilization

Ocean iron fertilization is an example of such a geoengineering technique. Iron fertilization attempts to encourage phytoplankton growth, which removes carbon from the atmosphere for at least a period of time. This technique is controversial due to limited understanding of its complete effects on the marine

ecosystem

, including side effects and possibly large deviations from expected behavior. Such effects potentially include release of nitrogen oxides, and disruption of the ocean's nutrient balance.

Natural iron fertilisation events (e.g., deposition of iron-rich dust into ocean waters) can enhance carbon sequestration. Sperm whales act as agents of iron fertilisation when they transport iron from the deep ocean to the surface during prey consumption and defecation. Sperm whales have been shown to increase the levels of primary production and carbon export to the deep ocean by depositing iron rich feces into surface waters of the Southern Ocean. The iron rich feces causes phytoplankton to grow and take up more carbon from the atmosphere. When the phytoplankton dies, some of it sinks to the deep ocean and takes the atmospheric carbon with it. By reducing the abundance of sperm whales in the Southern Ocean, whaling has resulted in an extra 200,000 tonnes of carbon remaining in the atmosphere each year.

Urea fertilization

Ian Jones proposes fertilizing the ocean with

urea

, a

nitrogen

rich substance, to encourage

phytoplankton

growth.

Australian company Ocean Nourishment Corporation (ONC) plans to sink hundreds of tonnes of urea into the ocean to boost -absorbing phytoplankton growth as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving 1 tonne of nitrogen in the Sulu Sea off the Philippines.

Mixing layers

Encouraging various ocean layers to mix can move nutrients and dissolved gases around, offering avenues for geoengineering. Mixing may be achieved by placing large vertical pipes in the oceans to pump nutrient rich water to the surface, triggering blooms of algae, which store carbon when they grow and export carbon when they die. This produces results somewhat similar to iron fertilization. One side-effect is a short-term rise in , which limits its attractiveness.

Seaweed

Seaweed

grow in shallow and coastal areas, and capture significant amounts of carbon that can be transported to the deep ocean by oceanic mechanisms; seaweed reaching the deep ocean sequester carbon and prevent it from exchanging with the atmosphere over millennia. In addition, Seaweed grows very fast and can theoretically be harvested and processed to generate biomethane, via

Anaerobic Digestion

to generate electricity, via

Cogeneration/CHP

or as a replacement for

natural gas

. One study suggested that if seaweed farms covered 9% of the ocean they could produce enough biomethane to supply Earth's equivalent demand for fossil fuel energy, remove 53 gigatonnes of per year from the atmosphere and sustainably produce 200 kg per year of fish, per person, for 10 billion people. Ideal species for such farming and conversion include ''

Laminaria digitata

'', ''

Fucus serratus

'' and ''

Saccharina latissima

''.

Physical processes

Biomass-related

Bio-energy with carbon capture and storage

Bio-energy with carbon capture and storage (BECCS) refers to biomass in power stations and boilers that use carbon capture and storage. The carbon sequestered by the biomass would be captured and stored, thus removing carbon dioxide from the atmosphere.

Burial

Burying biomass (such as trees) directly, mimics the natural processes that created fossil fuels.

Biochar burial

Biochar

is

charcoal

created by

pyrolysis

of

biomass

waste. The resulting material is added to a

landfill

or used as a soil improver to create terra preta. Addition of pyrogenic organic carbon (biochar) is a novel strategy to increase the soil-C stock for the long-term and to mitigate global-warming by offsetting the atmospheric C (up to 9.5 Pg C annually).

In the soil, the carbon is unavailable for

oxidation

to and consequential atmospheric release. This is one technique advocated by

scientist

James Lovelock, creator of the Gaia hypothesis. According to Simon Shackley, "people are talking more about something in the range of one to two billion tonnes a year."

The mechanisms related to biochar are referred to as bio-energy with carbon storage, BECS.

Ocean storage

If CO₂ were to be injected to the ocean bottom, the pressures would be great enough for CO₂ to be in its liquid phase. The idea behind ocean injection would be to have stable, stationary pools of CO₂ at the ocean floor. The ocean could potentially hold over a thousand billion tons of CO₂. However, this avenue of sequestration isn't being as actively pursued because of concerns about the impact on ocean life, and concerns about its stability.
A biological solution can be growing seaweed that can naturally be exported to the deep ocean, sequestering significant amounts of biomass in marine sediments.

River mouths bring large quantities of nutrients and dead material from upriver into the ocean as part of the process that eventually produces fossil fuels. Transporting material such as crop waste out to sea and allowing it to sink exploits this idea to increase carbon storage. International regulations on marine dumping may restrict or prevent use of this technique.

Geological sequestration

Geological sequestration refers to the storage of CO₂ underground in depleted oil and gas reservoirs, saline formations, or deep, un-minable coal beds.

Once CO₂ is captured from a point source, such as a cement factory, it would be compressed to ≈100 bar so that it would be a supercritical fluid. In this fluid form, the CO₂ would be easy to transport via pipeline to the place of storage. The CO₂ would then be injected deep underground, typically around 1 km, where it would be stable for hundreds to millions of years. At these storage conditions, the density of supercritical CO₂ is 600 to 800 kg / m³.

The important parameters in determining a good site for carbon storage are: rock porosity, rock permeability, absence of faults, and geometry of rock layers. The medium in which the CO₂ is to be stored ideally has a high porosity and permeability, such as sandstone or limestone. Sandstone can have a permeability ranging from 1 to 10⁻⁵ Darcy, and can have a porosity as high as ≈30%. The porous rock must be capped by a layer of low permeability which acts as a seal, or caprock, for the CO₂. Shale is an example of a very good caprock, with a permeability of 10⁻⁵ to 10⁻⁹ Darcy. Once injected, the CO₂ plume will rise via buoyant forces, since it is less dense than its surroundings. Once it encounters a caprock, it will spread laterally until it encounters a gap. If there are fault planes near the injection zone, there is a possibility the CO₂ could migrate along the fault to the surface, leaking into the atmosphere, which would be potentially dangerous to life in the surrounding area. Another danger related to carbon sequestration is induced seismicity. If the injection of CO₂ creates pressures that are too high underground, the formation will fracture, potentially causing an earthquake.Smit, Berend; Reimer, Jeffrey A.; Oldenburg, Curtis M.; Bourg, Ian C. (2014). ''Introduction to Carbon Capture and Sequestration''. London: Imperial College Press. .

While trapped in a rock formation, CO₂ can be in the supercritical fluid phase or dissolve in groundwater/brine. It can also react with minerals in the geologic formation to precipitate carbonates. See CarbFix.

Worldwide storage capacity in oil and gas reservoirs is estimated to be 675–900 Gt CO₂, and in un-minable coal seams is estimated to be 15–200 Gt CO₂. Deep saline formations have the largest capacity, which is estimated to be 1,000–10,000 Gt CO₂. In the US, there is an estimated 160 Gt CO₂ storage capacity.

There are a number of large-scale carbon capture and sequestration projects that have demonstrated the viability and safety of this method of carbon storage, which are summarized here by the Global CCS Institute. The dominant monitoring technique is seismic imaging, where vibrations are generated that propagate through the subsurface. The geologic structure can be imaged from the refracted/reflected waves.

The first large-scale sequestration project which began in 1996 is called Sleipner gas field, Sleipner, and is located in the North Sea where Norway's StatoilHydro strips carbon dioxide from

natural gas

with amine solvents and disposed of this carbon dioxide in a deep saline water, saline

aquifer

. In 2000, a coal-fueled synthetic natural gas plant in Beulah, North Dakota, became the world's first coal-using plant to capture and store carbon dioxide, at the Weyburn-Midale Carbon Dioxide Project. Several other sequestration projects have followed. The Energy Impact Center launched the OPEN100 project in February 2020, which is the world's first open-source blueprint for the design, construction and financing of a small, standard, pressurized water reactor. In September 2020, the United States Department of Energy, US Department of Energy awarded $72 million in federal funding to support the development and advancement of carbon capture technologies.

has been used extensively in enhanced crude oil recovery operations in the United States beginning in 1972. There are in excess of 10,000 wells that inject in the state of Texas alone. The gas comes in part from anthropogenic sources, but is principally from large naturally occurring geologic formations of . It is transported to the oil-producing fields through a large network of over of pipelines. The use of for enhanced oil recovery (EOR) methods in heavy oil reservoirs in the Western Canadian Sedimentary Basin (WCSB) has also been proposed. However, transport cost remains an important hurdle. An extensive pipeline system does not yet exist in the WCSB. Athabasca oil sands mining that produces is hundreds of kilometers north of the subsurface Heavy crude oil reservoirs that could most benefit from injection.

Chemical processes

Developed in the Netherlands, an electrocatalysis by a copper complex helps carbon fixation, reduce carbon dioxide to oxalic acid; This conversion carbon capture and storage, uses carbon dioxide as a feedstock to generate oxalic acid.

Mineral carbonation

Carbon, in the form of can be removed from the atmosphere by chemical processes, and stored in stable carbonate mineral forms. This process is known as 'carbon sequestration by mineral carbonation' or mineral sequestration. The process involves reacting carbon dioxide with abundantly available metal oxides–either magnesium oxide (MgO) or calcium oxide (CaO)–to form stable carbonates. These reactions are exothermic and occur naturally (e.g., the weathering of rock over geologic time periods).{“integral part of an established curriculum”

:CaO + →

:MgO + →

Calcium and magnesium are found in nature typically as calcium and magnesium silicate minerals, silicates (such as forsterite and serpentinite) and not as binary oxides. For forsterite and serpentine the reactions are:
: + 2 → 2 +

:+ 3 → 3 + 2 + 2

The following table lists principal metal oxides of Crust (geology), Earth's crust. Theoretically up to 22% of this mineral mass is able to form carbonates.

{, class="wikitable"
, -
!Earthen Oxide!!Percent of Crust!!Carbonate!!Standard enthalpy change of reaction, Enthalpy change
(kJ/mol)
, -
,
, 59.71
,
,
, -
,
, 15.41
,
,
, -
, CaO
, 4.90
, Calcium carbonate,
, −179
, -
, MgO
, 4.36
, Magnesium carbonate,
, −117
, -
,
, 3.55
, Sodium carbonate,
,
, -
, FeO
, 3.52
, Iron carbonate,
,
, -
,
, 2.80
, Potassium carbonate,
,
, -
,
, 2.63
, Iron carbonate,
,
, -
,
, 21.76
, All Carbonates

These reactions are slightly more favorable at low temperatures. This process occurs naturally over geologic time frames and is responsible for much of the Earth's surface

limestone

. The reaction rate can be made faster however, by reacting at higher temperatures and/or pressures, although this method requires some additional energy. Alternatively, the mineral could be milled to increase its surface area, and exposed to water and constant abrasion to remove the inert Silica as could be achieved naturally by dumping Olivine in the high energy surf of beaches. Experiments suggest the weathering process is reasonably quick (one year) given porous basaltic rocks.

naturally reacts with peridotite rock in surface exposures of ophiolites, notably in Oman. It has been suggested that this process can be enhanced to carry out natural Mineralization (geology), mineralisation of .

When is dissolved in water and injected into hot basaltic rocks underground it has been shown that the reacts with the basalt to form solid carbonate minerals. A test plant in Iceland started up in October 2017, extracting up to 50 tons of CO₂ a year from the atmosphere and storing it underground in basaltic rock.

Researchers from British Columbia, developed a low cost process for the production of magnesite, also known as magnesium carbonate, which can sequester CO₂ from the air, or at the point of air pollution, e.g. at a power plant. The crystals are naturally occurring, but accumulation is usually very slow.

Demolition concrete waste or recycled crushed concrete are also potential low cost materials for mineral carbonation as they are calcium-rich waste materials.

Electrochemical method

Another method uses a liquid metal catalyst and an electrolyte liquid into which CO₂ is dissolved. The CO₂ then converts into solid flakes of carbon. This method is done at room temperature.

Industrial use

Traditional cement manufacture releases large amounts of carbon dioxide, but newly developed cement types from Novacem can absorb from ambient air during hardening. A similar technique was pioneered by TecEco, which has been producing "EcoCement" since 2002. A Canadian startup CarbonCure takes captured CO₂ and injects it into concrete as it is being mixed. Carbon Upcycling UCLA is another company that uses in concrete. Their concrete product is called CO2NCRETE™, a concrete that hardens faster and is more eco-friendly than traditional concrete.

In Estonia, oil shale Bottom ash, ash, generated by power stations could be used as sorbents for mineral sequestration. The amount of captured averaged 60 to 65% of the carbonaceous and 10 to 11% of the total emissions.

Chemical scrubbers

Various carbon dioxide scrubber, carbon dioxide scrubbing processes have been proposed to remove from the air, usually using a variant of the Kraft process. Carbon dioxide scrubbing variants exist based on potassium carbonate, which can be used to create liquid fuels, or on sodium hydroxide. These notably include artificial trees proposed by Klaus Lackner to remove

carbon dioxide

from the

atmosphere

using chemical scrubbers.

Ocean-related

Basalt storage

Carbon dioxide sequestration in basalt involves the injecting of into deep-sea formations. The first mixes with seawater and then reacts with the basalt, both of which are alkaline-rich elements. This reaction results in the release of and ions forming stable carbonate minerals.

Underwater basalt offers a good alternative to other forms of oceanic carbon storage because it has a number of trapping measures to ensure added protection against leakage. These measures include “geochemical, sediment, gravitational and hydrate formation.” Because hydrate is denser than in seawater, the risk of leakage is minimal. Injecting the at depths greater than ensures that the has a greater density than seawater, causing it to sink.

One possible injection site is Juan de Fuca plate. Researchers at the Lamont-Doherty Earth Observatory found that this plate at the western coast of the United States has a possible storage capacity of 208 gigatons. This could cover the entire Greenhouse gas emissions by the United States, current U.S. carbon emissions for over 100 years.

This process is undergoing tests as part of the CarbFix project, resulting in 95% of the injected 250 tonnes of CO₂ to solidify into calcite in 2 years, using 25 tonnes of water per tonne of CO₂.

Acid neutralisation

Carbon dioxide forms carbonic acid when dissolved in water, so ocean acidification is a significant consequence of elevated carbon dioxide levels, and limits the rate at which it can be absorbed into the ocean (the solubility pump). A variety of different base (chemistry), bases have been suggested that could neutralize the acid and thus increase absorption. For example, adding crushed

limestone

to oceans enhances the absorption of carbon dioxide. Another approach is to add sodium hydroxide to oceans which is produced by electrolysis of salt water or brine, while eliminating the waste hydrochloric acid by reaction with a volcanic silicate rock such as enstatite, effectively increasing the rate of natural weathering of these rocks to restore ocean pH.

Obstacles

Rising fossil carbon extraction rates

As of year 2019, fossil carbon extraction and burning by humans has added a total of 440 GtC (gigatons of carbon) to the atmospheric, oceanic, and terrestrial regions of the Earth's biosphere. The majority has been added within the past half century. Global extraction rates have increased at about 2% annually for many years, and now exceed 10 GtC/year.

Financial costs

The use of the technology would add an additional 1–5 cents of cost per kilowatt hour, according to estimate made by the Intergovernmental Panel on Climate Change. The financial costs of modern coal technology would nearly double if use of CCS technology were to be required by regulation. The cost of CCS technology differs with the different types of capture technologies being used and with the different sites that it is implemented in, but the costs tend to increase with CCS capture implementation. One study conducted predicted that with new technologies these costs could be lowered but would remain slightly higher than prices without CCS technologies.

Energy requirements

The energy requirements of sequestration processes may be significant. In one paper, sequestration consumed 25 percent of the plant's rated 600 megawatt output capacity.
:''After adding CO₂ capture and compression, the capacity of the coal-fired power plant is reduced to 457 MW.''

See also

* Bio-energy with carbon capture and storage
* Blue carbon
*

Carbon capture and storage

* Oil_platform#Repurposing, Repurposing offshore drilling rigs for storing carbon

Notes

Further reading

*

External links

* GA Mansoori, N Enayati, LB Agyarko (2016)
Energy: Sources, Utilization, Legislation, Sustainability, Illinois as Model State
World Sci. Pub. Co.,

Carbon Sequestration Leadership Forum
International carbon capture and storage initiative.

UK Carbon Capture and Storage Consortium
Overview of the UK academic consortium focused on researching issues related to Carbon Capture and Storage.



The capture, utilization and disposal of carbon dioxide from fossil fuel-fired power plants.

Carbon Capture and Storage Information Center (Chinese + English)


MIT program covers carbon capture and storage (CCS)

Link to video, ''UK Looks for Natural Products in Kentucky's Unique Environments''

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Carbon capture and sequestration,
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