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Highly selective rare-earth separation using bacteria filters

By Mary Page Bailey |

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…
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