The growing dependence on rare earths requires new ways to extract them. Biomining with the help of microorganisms could be promising.
Early in the history of rare earths – a group of 17 chemical elements with similar properties – was the Swedish amateur geologist Carl Arrhenius: in 1787 he found an unknown, heavy, black stone in the Ytterby mine (near Stockholm). He called it “Ytterbit” and gradually more and more elements, the rare earths, were found in it. Austrian chemist Carl Auer von Welsbach was the first to recognize its usefulness; he used, for example, B. Yttrium, lanthanum and cerium for perfect mantles (efficient gas lamps). Today, rare earths are ubiquitous; Without them there would be no cell phones, wind turbines, robots, etc. The need has multiplied, and although these elements are widely available in small quantities, China has a de facto monopoly.
To escape this dependence, new productive deposits and recycling processes are sought. However, this is complex and expensive, so new ideas are needed. One of them comes from an unexpected place: biology. Some microorganisms (bacteria, microalgae) are capable of dissolving these metals from raw materials or binding them to themselves.
Biomining is already being practiced, for example, in the extraction of copper, gold, uranium or nickel from poor ores or mine wastewater. Asian and Australian researchers led by Phong HN Vo (University of Technology Sydney) have now investigated the potential of various biomining methods (including bioleaching, bioprecipitation, biosorption, bioaccumulation or bioflotation) for rare earths. Compared to mining and metallurgical processes, biomining has some special characteristics: the dissolution of metals takes a certain amount of time – months to years – and the microorganisms used must be fed with carbohydrates. But everything indicates that these methods could be used effectively and efficiently (more than 80 percent yield) to extract rare earths – and are very environmentally friendly (Science of the Total Environment 908, 168210).
The study found that biomining is most promising when it comes to coal ash (which contains a lot of metals) – when corn scraps or potato waste are used as food for microorganisms and as an energy source for processes. The researchers recommend that such procedures be developed to make them ready for practical use.
The author headed the research department at “Presse” and is a science communicator at AIT.
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