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Discovery of strange bacteria that help extract rare earths from wastewater

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Rare earth elements (REEs) are a group of 17 chemical elements that get their name because they are commonly found in low concentrations (0.5 to 67 ppm) in the earth’s crust.

Since it is indispensable in modern technologies such as light emitting diodes (LEDs), mobile phones, electric motors, wind turbines, hard drives, cameras, magnets and energy-saving lamps, the demand for it has been steadily increasing in recent times. several decades, and demand is expected to increase by 2030.

Due to their rarity and demand, they are very expensive: for example, a kilogram of neodymium oxide currently costs about 200 euros, while the same amount of terbium oxide costs about 3,800 euros. China has a near monopoly on the extraction of rare earths (or rare earth metals) despite the announcement of the discovery of huge promising reserves (over 1 million metric tons) in Kiruna, Sweden in January 2023.

Another source of these valuable minerals can be wastewater from the metallurgical and mining industries, as well as from enterprises involved in the processing of electronics.

This possibility was outlined by German scientists in an article published in the journal Frontiers in Bioengineering and Biotechnology.

A dozen exotic bacteria have been found to passively collect #rare earth elements from #Wastewater@frontiersinhttps://t.co/k8n9fLf1mF https://t.co/uOREb7AwLZ

— Phys.org (@physorg_com) February 28, 2023

Thomas Brock and his colleagues at the Technical University of Munich conducted laboratory experiments on 12 rather strange species of cyanobacteria that inhabit deserts, salt water reservoirs, polluted soils and other extreme niches.

Experiments have shown that the biomass of some photosynthetic exotic cyanobacteria can efficiently absorb rare earth elements from mining wastewater or e-waste processing, which can then be isolated from their biomass and collected for reuse.

“We have optimized the conditions for the absorption of rare earth elements by the biomass of cyanobacteria and characterized the most important chemical mechanisms of their binding. These cyanobacteria could be used in future environmentally friendly processes to extract rare earth elements and treat industrial wastewater at the same time,” said Dr. Brock.

Biosorption is a passive metabolic process of rapid and reversible binding of ions from aqueous solutions to biomass.

Brock and colleagues measured the biosorption potential of the rare earth elements lanthanum, cerium, neodymium, and terbium using 12 strains of cyanobacteria in vitro culture (a method for developing microorganisms, bacteria, and other biological assets).

The biotechnological potential of most of these strains has not been previously evaluated. They have been selected from highly specialized habitats such as the arid soils of the deserts of Namibia, the surface of lichens around the world, Lake Natron in Chad, rock crevices in South Africa or polluted streams in Switzerland.

The scientists found that a new, unknown species of Nostoc, a genus of cyanobacteria, had the highest ability to biosorb ions of these four rare earth elements from aqueous solutions, with an efficiency of 84.2 to 91.5 mg per gram of biomass. Scytonema hyalinum had the lowest potency at 15.5 to 21.2 mg per gram. Also effective were the bacteria Synechococcus elongates (Synechococcus elongates) elongate, Desmonostoc muscorum, Calothrix brevissima and a new, unidentified species Komarekiella.

The scientists found that bioabsorption was highly dependent on acidity: it was highest at pH five to six and steadily declined in more acidic solutions.

The process is most effective in the absence of “competition” on the biosorption surface for the biomass of cyanobacteria from positive metal ions other than rare earth elements such as zinc, lead, nickel, or aluminum.

The team used a technique called infrared spectroscopy to identify chemical functional groups in biomass that are primarily responsible for the biosorption of rare earth organisms.

The scientists concluded that bioabsorption of rare earth elements by cyanobacteria is possible even at low concentrations of metals. The process was also fast, for example most of the cerium in the bioavailable solution was taken up within five minutes of starting the reaction.

Source: phys.org.

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