March 30, 2023

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Exotic bacteria show promise as recyclers of rare earth elements – Ars Technica

Zoom in / One of the species identified in this work.

Thomas Brook

The demand for rare earth elements is increasing 315,000 tons By 2030. Meanwhile, more than 40 million tons of e-waste — computers, cell phones, and other discarded electronic devices — is generated each year. Some of these wastes contain the same valuable elements that are facing increased demand.

Over the years, several notable methods for the recovery of spent or waste-based REEs have been proposed, such as urban mining or nano filtration systems in tables. One ongoing idea is to use microorganisms such as bacteria to “biosorption” of desired materials—a passive biological process in which organisms bind and remove materials from an aqueous solution. The technology has not yet been deployed on an industrial scale, but some researchers point out that their latest findings represent a major step forward.

in The last paperThomas Brock, a professor at the Technical University of Munich who studies synthetic biotechnology and sustainability, and colleagues describe the identification of 12 exotic cyanobacteria that are particularly good at absorbing rare earth elements. These types can be used to retrieve desired items, while also cleaning land and water. “[I]This is not something we expected in any way,” Brock told Ars.

The unusual suspects

The research took six years. The team started by examining different types of algae and bacteria, but none of them absorbed the rare earth elements well. Therefore, they turned their attention to dozens of species of cyanobacteria. Some came from environments that were particularly inhospitable to most forms of life. For example, Lake Natron, which is unusually alkaline, with a pH of about 10and sees the temperatures it can reach 60 degrees Celsius (or 140 degrees Fahrenheit). According to Brock, it is unclear if how these organisms evolved to thrive in these environments contributed to their ability to devour rare earth elements.

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Often, species came from incredibly specialized habitats such as the arid desert soils of Namibia, the alkaline Lake Natron in Chad, the rocky crevices of South Africa, or the polluted streams of Switzerland. These were “really unique and extreme environments,” Brock said.

Most of these bacteria have not been evaluated for potential bioremediation before. In the lab, the teams subjected the cultures of the different species to aqueous solutions containing the rare earth elements lanthanum, cerium, and neodymium, and then checked to see how well the elements were retained on their surface using infrared spectroscopy.

One previously uncharacteristic type of Nostock Cyanobacteria performed the best. Its bioavailability of the four rare earth elements from solutions resulted in a withdrawal of between 84.2 and 91.5 mg of the metal per gram of biomass. It was the worst performance Scytonema hyalenum At a rate of 15.5 to 21.2 mg per gram of biomass. However, the paper noted that how well each filter performed depended on acidity and that the processes were most efficient when there were no other metals in the solution to compete with the target rare earth element.

The dirty, er, clean dozen

It is also possible, and relatively easy, to recover desirable REEs from biomass. It would simply be a matter of changing the pH of the solution – with an acid or something like lye – or the salinity. The elements are functionally only “washed” from the biomass. Returning the solution to its previous state afterwards will allow the process to start over, which means that cyanobacteria cultures can be reused.

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“It’s not a one-two deal where at the end of the peg you have to burn biomass to recover your minerals,” Brock said.

Researchers or industrial actors could create bioreactors — specialized vessels that contain microbial biomass — for many uses in the future. First, they could be used to collect rare earth elements from e-waste dumps, although this would require converting the e-waste into a form microorganisms can use. This would provide environmental benefits by removing waste from these areas and potentially create jobs in parts of the world Where e-waste is shipped regularly From Global North, locations such as Nigeria, Ghana and Tanzania. Then, Brock added, they could be used to clean up and recover these items from industrial runoff, such as mining or from the chemical industry.

According to Brock, the research could be a huge step forward. From this point on, the researchers hope to expand exponentially—something not yet done in this field. They plan to work with partners in different industries to do this, though that’s a daunting prospect given that it’s a fairly specialized process: It’s not like growing corn in agriculture, nor is it like traditional metal refining methods. Despite this, the researchers are hopeful about the results.

“I think we’re at a step now where we can say, ‘Hey, we can make this work,'” Brock said.

Frontiers, 2023. DOI: 10.3389/fbioe.2023.1130939 (about DOIs)