A new method to extract rare earths in a sustainable way

A new method to extract rare earths in a sustainable way

By exploiting the affinity of a bacterial proein for rare earths, a team of researchers has developed a green method for their extraction

A piece of Yttrium, one of the 17 rare earths (Wikipedia - Jan Anskeit , CC BY-SA 4.0 , via Wikimedia Commons) In cell phones, hard drives, fiber optics, electric and hybrid vehicles, and even batteries, in lasers, monitors, wind turbines. Rare earths - a group of 17 chemical elements - are everywhere and realistically they will be more and more with the ecological transition. But finding, or rather extracting, these elements is far from easy, both from a technological and an environmental point of view (a hot topic, consequently, also in political matters). For this reason, green processes would also be necessary for their extraction. And something seems to be moving right in the field.

Researchers from some US universities that use the pages of the journal Acs Central Science to do so announce this: they have found a protein of bacterial origin that is able to bind rare earths , and which could therefore be used as a "filter" to catch these elements and separate them from the rest. And by “rest” the researchers also mean poorly enriched sources, where rare earths are mixed with other metals, present in small quantities and not always easy to find. This is the case, the authors explain, of some industrial waste, but also electronic ones.

The idea that came to researchers is to exploit the affinity of a bacterial protein - lanmodulin - which has a very strong specificity for rare earths. By immobilizing it on agarose balls (a polysaccharide polymer), in turn packed inside a column, it can be used to filter rare earths starting from a solution that contains them. Like? By playing on chemical conditions - such as ph - it is possible to "detach" at a later time the rare earths bound to the protein, effectively purifying them, as summarized in the graphic abstract of the paper.

#ASAP Rapid, all- aqueous recovery and heavy / light (eg Nd / Dy) separation of #rareearths using a #lanmodulin protein column from Dan Park, @CotruvoLab, and coworkers @CMI_hub @Livermore_Lab @PSUScience https://t.co/kunJDXm0RP pic.twitter. com / p6ENUyORUu

- ACS Central Science (@ACSCentSci) October 11, 2021

“Even in complex solutions where less than 0.1 % of metals are rare earths - and we are talking about an extremely low amount - we were able to successfully extract first and then separate lighter rare earths from heavier rare earths in a single step, "explained Joseph Cotruv of Pennsylvania State University, including the authors of the paper. But not only: as a proof of concept, researchers have shown that this method is able to separate, with high purity, even pairs of rare earths: such as neodymium from dysprosium and yttrium from neodymium. Furthermore, importantly, the protein remains stable through different absorption / desorption cycles, explain the authors, allowing it to be used over and over again to enrich rare earths starting from different solutions. The balls used as a support are bio-renewable, they add, and no organic solvents are used in the process. This, combined with the high purification capacity, even starting from raw materials that contain few rare earths, makes their green method ready to be investigated in the future. Maybe also optimizing the affinities of the protein for the different elements.

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