Las mezclas de elementos pertenecientes a las así llamadas tierras raras (REMs) son muy difíciles de separar, pero un equipo de investigadores de la Universidad de Harvard (www.seas.harvard.edu) ha desarrollado un método para la extracción eficiente de REM con un alto nivel de selectividad. Aprovechando la compleja química superficial de filtros recubiertos de bacterias, el equipo descubrió que esencialmente puede adaptar el filtro para el control de la bio-absorción de ciertos REM, permitiendo a otros a pasar por el filtro para la extracción. La clave para esta selectividad es la afinidad de grupos superficiales de las bacterias para absorber diferentes REM.
Mixtures of rare-earth metals (REMs) are notoriously difficult to separate, but a team of researchers from Harvard University (Cambridge, Ma.; www.seas.harvard.edu) has developed a method for efficiently extracting REMs with a high level of selectivity. By taking advantage of the complex surface chemistry of bacteria-coated filters, the team discovered that it could essentially tailor the filter to control the bio-absorption of certain REMs while allowing others to pass through the filter for extraction. The key to this selectivity is the affinity of the bacteria’s surface groups for bioabsorbing different REMs. By passing various low-pH solutions through the filter prior to any REMs — a step the team calls “pre-protonation” — certain surface groups become occupied with protons, and the REMs for which these occupied groups have affinity will pass through the filter (see diagram). The team found that pre-protonation with subsequently lower-pH solutions resulted in the extraction of heavier REMs. By fine-tuning the pre-protonation step, the filter can differentiate between extremely similar REMs, even among neighboring lanthanides. The REMs are recovered from the filtrate using traditional extractive metallurgy techniques.
The team believes the scaleup potential for this process is promising, and provides many benefits over current industrial practices. REMs are typically separated using liquid-liquid extraction processes that can often require over 50 passes to achieve useful purity. The bacteria-filter technology would not only work more efficiently, and with a much smaller footprint, but would also be more environmentally benign, as fewer harsh chemicals are required.
To further the technology’s potential for customization, the team is investigating the use of various types of bacteria with different binding affinities. Recycling REMs is another area where the technology could be employed, and the team has demonstrated the use of bacteria filters for REM recovery from magnets in the laboratory.
Fuente: http://www.chemengonline.com
