Carbon dioxide is a greenhouse gas in our atmosphere. There are many ways in which carbon dioxide can enter the atmosphere; respiration of living things, volcanic eruptions, and in the production and burning of fossil fuels. Since the industrial revolution the amount of carbon dioxide released into the atmosphere has increased (Figure 1). This has been linked with the enhanced greenhouse effect and is considered a major contributor to climate change.
Figure 1. Global carbon dioxide emissions (gigatons of carbon per year) (Earth Observatory, 2011)
As a global priority, industry and government are investigating how to minimise the amount of carbon dioxide which is released through human activities into the atmosphere. Although there are some companies using carbon capture and storage methods this is currently very costly.
One current method of carbon storage is geological sequestration in deep saline aquifers. Saline aquifers are large underground rock formations (usually sandstone) which contain highly concentrated brine in the pore spaces of the rock. Saline aquifers have been considered to have no benefit to humans and are therefore a perfect storage site for carbon. When CO2 is injected into the aquifer, it chemically reacts with the brine to form “precipitates” which are solid chunks of material. Research has suggested that “for well-selected, designed and managed geological storage sites, CO2 could be trapped for millions of years” (BGS, 2020)
There are large saline aquifers below the North Sea, mainland Europe and the Texas Gulf Coast. One site, which has been in use since 1996, has already stored 11 million tonnes of CO2 and reports a capacity of 600 billion tonnes – so there is massive potential for future storage.
- Find out more about the Sleipner Gas Field.
One issue with carbon storage in a saline aquifer is that the more saline the aquifer is the less capacity it has.
Here is an experiment that you can conduct at home to investigate this relationship between salinity and solubility.
- For more information and experiments on Carbon Capture and Storage methods have a look at the CCUS WASP STEM booklet.
- Here is a short animated video on carbon capture in a saline aquifer.