The discovery of strange bacteria that help extract rare earth elements from wastewater

Rare earth elements (REE) are a group of 17 chemical elements, which got their name because they usually occur in low concentrations (between 0.5 and 67 parts per million) within the Earth's crust.

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Since it is indispensable in modern technology, such as light-emitting diodes (LEDs), mobile phones, electric motors, wind turbines, hard disks, cameras, magnets, and low-energy lamps, the demand for it has increased steadily over the past few decades, and it is expected Demand should increase further by 2030.

As a result of their rarity and demand, they are very expensive: for example, a kilo of neodymium oxide currently costs about 200 euros, and the same amount of terbium oxide costs about 3,800 euros. China has almost a monopoly on rare earth element (or rare earth metal) mining, despite the announcement of the discovery of huge promising reserves (more than 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 companies involved in the processing of electronics.

This possibility was outlined by German scientists, in a paper published in the journal Frontiers in Bioengineering and Biotechnology.

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

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

"We optimized the conditions for uptake of rare earth elements by the biomass of cyanobacteria, and characterized the most important chemical mechanisms for their binding. These cyanobacteria can be used in future environmentally friendly processes to recover rare earth elements and simultaneously treat industrial wastewater," 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 by 12 strains of cyanobacteria in in vitro culture (a method for developing microorganisms, bacteria and other biological assets).

Most of these strains have not been previously evaluated for their biotechnological potential. They were sampled from highly specialized habitats such as the arid soils of the Namibian deserts, the surface of lichens around the world, Lake Natron in Chad, or crevices in rocks in South Africa. or polluted streams in Switzerland.

The scientists found that a new, uncharacterized species of Nostoc, a genus of cyanobacteria, had the highest capacity for biosorption of ions of these four rare earth elements from aqueous solutions, with efficiencies ranging from 84.2 to 91.5 mg per gram of biomass. , while Scytonema hyalinum had the least efficient 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, unspecified species of Komarekiella.

The scientists found that bioabsorption strongly depended on acidity: it was highest between pH five and six, and decreased steadily in increasingly acidic solutions.

The process was most effective when there was no "competition" on the biosorption surface for cyanobacterial biomass from positive ions of metals other than rare earth elements such as zinc, lead, nickel or aluminum.

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

The scientists concluded that bio-uptake of rare earth elements by cyanobacteria is possible even at low metal concentrations. The process was also fast, for example, most of the cerium in the bioavailable solution was absorbed within five minutes of starting the reaction.

Source: phys.org