Clay might have a role in carbon capture
09 April 2015
Many materials are being tested for the purpose of capturing CO2. New results show that ordinary clay can work just as effectively as more advanced materials.
"It is quite remarkable that clay can capture as much CO2 as other materials that are being investigated," says Professor Jon Otto Fossum at the Norwegian University of Science and Technology (NTNU).
Clay offers many benefits compared to other materials, particularly because other potential materials can be expensive, difficult to produce, toxic and not particularly environmentally friendly.
A possible practical future use of this discovery could be to include clays in CO2 filters for industrial-scale CO2 emissions reduction.
"What we are doing is basic research," Fossum says. "It will take more research to develop the technology, so we don’t expect clay-based CO2 capture to be readily available anytime soon."
A good material for capturing CO2 must meet specific requirements. It should have a large surface area and good adsorbtion capability. It should be able to capture CO2 selectively before it captures other molecules, it should not need a lot of energy for it to work, and it must be reusable. Moreover, it must be inexpensive and environmentally friendly.
Certain clay minerals meet these criteria, particularly smectite, a group of clay minerals that swell in contact with water, which are known as layered nanosilicates.
The researchers used synthetic smectite in their experiments. Artificial clays can actually be inexpensive to make.
The researchers found that CO2 in gaseous form binds to smectite, and that it is not only the smectite clay surfaces in themselves that are responsible for binding CO2, but principally that ions associated with the clay surfaces are the active capturers.
A smectite clay called lithium-fluorohectorite can retain CO2 at temperatures up to 35°C at ambient pressure. The CO2 that is captured by the clay is released when it is heated to temperatures above this limit, which allows CO2 capture to be controlled.
"Our experiments show that this kind of smectite can capture and retain as much CO2 as other materials that have been studied for this purpose," Fossum says.
NTNU researcher, Leander Michels and Professor Fossum led the research effort, in cooperation with researchers from the Institute for Energy Technology in Kjeller, Norway, and scientists from the Slovak University of Technology, the MaxIVLab at Lund University and the Universidade de Brasilia. The results were recently published in the journal, Scientific Reports.