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Ordinary Clay Effective Carbon Capture, Say Experts

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Carbon capture and storage (CCS) is expected to play a major role in the reduction and management of greenhouse gas discharges from large point sources.

Ionic liquids, metal-organic framework (MOF) materials and even sea urchin-inspired materials are being examined for the purpose of confining waste carbon dioxide at one of the known root causes: industrial smokestacks. These suggested substances, however, are either hard to produce or cost too much.

Based on a recent scientific report, Norwegian researchers have found that ordinary clay could be as effective as these more advanced materials in CCS.

Ph.D. candidate Leander Michels and Prof. Jon Otto Fossum from the Department of Physics at the Norwegian University of Science and Technology (NTNU) are leading a team of scientists from the Universidade de Brasilia, MaxIVLab at Lund University, Slovak University of Technology and Institute for Energy Technology located at Kjeller, Norway on this matter.

The researchers discovered that, at ambient pressure, smectite clay met the requirements for good CCS. Its properties include: having a large effective surface area; capacity to absorb; ability to selectively capture carbon dioxide molecules before capturing other molecule types; requirement of minimal energy; and reusability.

When subjected to water or moisture, smectite clay can initiate a process known as swelling, resulting in an increased surface area. From this point, carbon dioxide molecules in those gases unite with ions in the surface area of the smectite clay.

A smectite clay, specifically lithium-fluorohectorite, can keep carbon dioxide at temperatures not exceeding 35 degrees Celsius (95 degrees Fahrenheit) at ambient pressure. The carbon dioxide that is confined by the clay is released when it is heated to temperatures above this limit, which permits the captured carbon dioxide to be controlled.

The researchers found that carbon dioxide in gaseous form binds with smectite. It is not only the smectite clay surfaces in themselves that are responsible for binding carbon dioxide, but principally the ions associated with the clay surfaces serve as the trap.

"Our experiments show that this kind of smectite can capture and retain as much carbon dioxide as other materials that have been studied for this purpose," said Fossum. He added, however, that the research is still in its early stages, and it will be some time before such filters could be in use.

The complete study is published in the journal Scientific Reports.

Photo: Paul Lim | Flickr

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