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Modern life is closely related to a set of 17 elements located at the bottom of the periodic table. Known as rare earths, many of these metals are very magnetic and find use in computer technologies, green energy and others. However, because of rising prices, legal problems and the difficulty of mining, preserving their supply is a major scientific and political challenge.
Several ERs, such as yttrium (Y) and europium (Eu), are used as phosphors in fluorescent lamps (FL). These lamps replace more and more conventional incandescent lamps, but have a limited life. End-of-life LFs are therefore a potentially huge source of renewable energy – an example of "technospheric extraction" – but stringent and polluting processes are needed to actually extract these metals from spent phosphors. Now, a team led by Kanazawa University in Japan has developed a cleaner method.
As stated in Waste Management, instead of using acid extractants to dissolve the ERs trapped in spent lamps, the Kanazawa team turned to chelator chemistry. Chelators – organic compounds containing elements such as N or O bonds with metals through the donation of electrons. This allows them to smoothly extract the ER from the solid mbad of a spent phosphor without the need for strong acids.
"An ideal type of compound chelator is known as amino-polycarboxylates," says co-author of the study, Ryuta Murase. "These are already being used to remove toxic metals from solid waste, and we have also found that they are also very effective at extracting ERs from spent phosphors, particularly yttrium and lanthanum, which are used in red phosphors more chemically reactive, EDTA chelator, probably because it forms the strongest complexes with metals. "
To boost the extraction rate, the team added a second ingredient to its process: the chemical-mechanical energy. The "planetary ball milling" – grinding of a solid into fine particles between layers of small hard balls in a rotating chamber – has proven to increase the yield of ER during chelation treatment. Indeed, once milled, the larger surface of the sprayed phosphors facilitated access to leachable metals.
"We worked hard to optimize the process down to the smallest detail, including temperature, pH, grinding speed, bullet size and other factors," said the corresponding author, Hiroshi Hasegawa. "Our efforts have paid off and the most economically important metals have been leached from used lamps with recovery rates of 53% to 84% .Renewable energy recycling will be vital for sustainable technology, and we hope show that this can be done in a clean and efficient way. " "
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Material provided by Kanazawa University. Note: Content can be changed for style and length.
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