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.