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New insights offered by near infrared spectroscopy into the mineralogy of carbonate rocks could help improve the outlook for carbon capture and storage in efforts to reduce the effect of carbon dioxide emissions on the global climate. Despite the apparent downward trend in global average temperatures scientists have observed over the last decade, the consensus is that climate change due to anthropogenic emissions of carbon dioxide into the atmosphere will prevail and take us into an era of potentially devastating global warming. As such, huge numbers of research applications have been written and grants awarded to novel technologies aimed at ameliorating the problem. Some of these focus on the notion of developing renewable energy sources. Others are pitched at reducing emissions by improving efficiency. A third category looks at the idea of trapping carbon dioxide to stabilise and even reduce atmospheric levels of this greenhouse gas. Carbon capture and storage, or geosequestration of carbon dioxide, has been proposed to reduce the greenhouse effect of increased carbon dioxide in the atmosphere. Now, researchers at the Queensland University of Technology have turned to near infrared spectroscopy (NIR spectroscopy) to help them formulate a new approach to CO2 sequestration by identifying and classifying the kinds of carbonate rocks that might be formed if a liquefied form of the greenhouse gas were to be pumped deep below the earth's surface. They explain that such a process of geosequestration would involve locking the carbon dioxide into the mineral bedrock as smithsonite and magnesium carbonates. The carbonate rocks, such as smithsonites, include some of the most highly coloured and prized precious gem stones. "Here at the Queensland University of Technology we set out to understand the basis of the colour changes in carbonate rocks", explains project leader Ray Frost of the Inorganic Materials Research Program at QUT. The team, which includes QUT's visiting professor Jagannadha Reddy, Matthew Hales and Daria Wainhas, used NIRS to help them understand the significance of the very small changes in trace element concentrations in these minerals that give rise to colour changes. Frost explains that in the NIR spectra of smithsonite minerals, the main peaks observed are due to the presence of anions of OH- and CO32- and to iron and copper ions. The presence of calcium, iron(II), copper(I), cadmium and zinc ions leads to significant band shifts in the electronic spectral region (11000 to 7500 cm-1. The vibrational modes of hydroxyl and carbonate ions at 7300 to 4000 cm-1 also allowed the team to distinguish between the various smithsonites. "We will now be able to use visible-near infrared spectroscopy in combination with multispectral remote sensing to greatly enhanced the accuracy of geological mapping," Frost adds. Such remote sensing can be carried out from the air, or even from space and perhaps even provide a survey of likely repositories for carbon geosequestration. Whether or not carbon sequestration ever becomes a viable method of climate control is a different matter, but the work of Frost and his colleagues has broader implications for fundamental extraterrestrial science nevertheless. The same spectroscopic technique could also have relevance to the identification of minerals on Mars and other planets and their moons. Understanding the matter which makes up our solar system has challenged scientists for centuries. "We are now a step closer to being able to identify which minerals occur on Mars and other planets in the solar system," Frost said. Related links:
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