Wooden it be nice? X-raying contaminants

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  • Published: May 15, 2014
  • Author: David Bradley
  • Channels: X-ray Spectrometry
thumbnail image: Wooden it be nice? X-raying contaminants

Wooden heart

Seeing the wood for the trees, a path to recycling treated wood, photo by David Bradley

Researchers in Germany are using X-ray fluorescence analysis, near-infrared spectroscopy and ion mobility spectrometry to help them identify potentially harmful contaminants in wood destined for recycling. The identification of the contaminants, preservative residues then allows appropriate supercritical fluid treatment to be used to extract them efficiently. The work is part of bigger recycling and raw materials effort showcased recent at IFAT Trade Fair in Munich.

Approximately 70 billion tonnes of raw materials are dug out of the ground, harvested from the oceans, hacked down from forests worldwide each year, a doubling since the 1970s. There is thus an urgent need to consider the finite nature of these resources and the possibilities of recycling much more than we do today. Researchers at the Fraunhofer Institutes and many other teams across the globe are working on novel approaches to recycling and their approach to what they refer to as "molecular sorting" was highlighted at the beginning of May 2014 at the IFAT Trade Fair in Munich, Germany.

Recycling 2.0

Recycling wood is still in its infancy in Germany, the team reported. Up until now, only about a third of the approximate eight million tonnes of scrap wood is re-used annually. One reason for such a low recycling rate here and elsewhere is the strict regulations concerning the handling of scrap wood. These regulations put in place for the sake of human safety and environmental production prescribe that material coated with organic compounds containing halogens or wood treated with wood preservatives may not be re-used except under very strict conditions Thankfully, molecular sorting could remediate such contaminated would and so allow it to be re-used without breaking regulations nor compromising health and the environment.

In order to recycle scrap wood, any harmful substances contained within must first be identified. To do this, researchers at the Fraunhofer Institute for Wood Research/Wilhlem Klauditz Institute in Braunschweig, Germany, have now used X-ray fluorescence analysis, NIRS and ion mobility spectrometry. These techniques reveal the presence of organic wood preservatives, which can then be dissolved in non-toxic and entirely controllable supercritical fluids as solvents. The advantages of using SCFs over conventional organic solvents is that the process is carried out under pressure in the supercritical region of water, carbon dioxide or other substance, and with release of pressure the "solvent" can be tapped off and retrieved at 100 percent as the vapour for reuse without leaving a residue.

Heavy metal from wood

Team leader Peter Meinlschmidt of WKI points out that the next step will be to find a similar method for concentrating any heavy metals present in the wood and to apply wet chemical processes or pyrolysis approaches to remove those. Even small quantities of precious metals or rare earths recovered from scrap wood, ores and combustion slags would be useful given the rarity of many metals of technological importance. Indeed, Fraunhofer teams also showcased approaches for extracting valuable resources as part of the large Molecular Sorting for Resource Efficiency project.

"The separation processes take place initially at the smallest level required, i.e. we go down to the molecular or even atomic levels," explains the project's coordinator, Jörg Woidasky from the Fraunhofer Institute for Chemical Technology ICT in Pfinztal near Karlsruhe, Germany. X-ray and other techniques are a critical part of the assessment of waste materials for recycling so that an appropriate separation technique can be used.

Related Links

IFAT Trade Fair, Munich, May 2014: "World's leading trade fair for water, sewage, waste and raw materials management"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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