What is Carbon Sequestration?
Carbon sequestration is a multifaceted strategy aimed at capturing and securely storing atmospheric carbon dioxide. Removing the excess CO2 in the air caused by human activities will curb global warming and mitigate climate change.
Reducing CO2 emissions is undoubtedly important, but tackling the residual CO2 that has built up in the atmosphere since the beginning of industrialisation is equally urgent.
There are various methods that have been developed to capture carbon dioxide, such as capturing at the source of emissions. But one which stands out for its potential scalability and efficiency is Direct Air Capture (DAC). For more detail on DAC technology, see How Does Direct Air Capture Work?
Types of CO2 Sequestration
There are two main approaches to carbon sequestration: biologic and geologic.
What is Geological Sequestration?
Simply put, geological sequestration is storing carbon dioxide in geological formations underground.
Geological Mineralization: Transforming CO2 into Rock
Once CO2 is captured, the next challenge is ensuring its long-term storage in a secure and environmentally friendly way. This is where geological mineralization comes into play, specifically through basalt and peridotite rock formations.
The captured CO2 is mixed with water, becoming much like fizzy soda water, and then pumped deep underground into the porous rock formation reservoir where the chemical process of geological sequestration begins. Alternatively, it can be compressed to a liquid state and then injected deep into the Earth. The CO2 is securely trapped under a cap-rock, a layer of impermeable rock that seals in the carbon dioxide.
Basalt and peridotite are types of volcanic rocks abundant in magnesium and calcium minerals. When exposed to CO2, a natural mineralization process occurs, where the CO2 reacts with these minerals to form stable carbonates. This process effectively turns the gaseous CO2 into solid rock, securely storing it for geological timescales.
The chemical reactions involved in this mineralization process are not only efficient but also environmentally benign, offering a sustainable and natural solution to the carbon storage challenge.
Now let’s look a little deeper into the mechanics of geological mineralization.
Carbonation Reactions:
CO2 reacts with minerals in basalt and peridotite, primarily forming carbonates. This process mimics natural weathering but at an accelerated rate.
Stability and Permanence:
The resulting carbonates are stable and can remain locked in the rock formations for tens of thousands of years, preventing the release of CO2 back into the atmosphere.
Other Geological Carbon Sequestration Methods
We have focused on geological mineralization in basalt formations, but there are other options to store the CO2. (This article by NETL explains carbon storage in depth.)
- Saline Formations
- Depleted Oil and Gas Reservoirs
- Unmineable Coal Seams
- Organic-Rich Shales
Is There Enough Space to Store Carbon Geologically?
The simple answer – yes. The International Energy Agency reported that there is an estimated 8,000 to 55,000 billion tonnes of CO2 storage capacity in saline rock formations and depleted oil and gas wells. This accounts for both the onshore and offshore capacity. However, in reality, not all this capacity is entirely suitable for CO2 storage, with both technical and commercial feasibility issues to consider.
What is Biological Sequestration?
On the other hand, biological carbon sequestration is the capturing and storing of atmospheric CO2 in the natural environment through biological processes. While this happens naturally, especially in ‘carbon sinks’ like forests, peatlands and oceans, it can be enhanced by human activities. Examples include afforestation, bioenergy with carbon capture and storage (BECCS), ocean fertilisation or alkalinity enhancement, and enhanced weathering of rocks by crushing and spreading them.
The down-side of biological sequestration is the vulnerability of nature – fires can destroy forests, land-use can change and intense climate events can cause great damage – which will result in the captured CO2 being released again into the air.
CO2 Capture and Sequestration is Paving the Way for a Sustainable Future
As we look for ways to fight climate change, technologies for capturing and storing carbon emerge as promising solutions. By harnessing the power of nature combined with developing technology, we can not only reduce current CO2 emissions but actively reverse the climate change, paving the way for a more sustainable and resilient future.
For more: What is the Utilization of CO2?