By using chelator chemistry and mechano-chemical energy to extract rare earth materials from phosphors in fluorescent lamps, a team of scientists at Kanazawa University hopes to shorten the supply chain by cleanly getting at the materials they need using better recycling methods. This means the rare earth components could be recycled and reused locally rather than continually having to be imported.
Recovery rate using the new method is between 53% and 84%, and being able to recycle already-mined materials will significantly shorten the supply chain. With 90% of all rare earth mines located in China, scarcity, fluctuating prices, and on-again, off-again import and export tariffs significantly increase the difficulties of using these materials in catalytic converters, electronic devices, fuel cells, batteries, and in the petroleum refining process.
Yttrium (Y) and europium (Eu) are used as phosphors in fluorescent lamps, which unfortunately don’t last forever. Extracting the metals from used fluorescents, or “technospheric mining,” has led to polluting processes involving acid extractants. But by substituting organic compounds containing nitrogen or oxygen that bond to metals via electron donation, rare earths can be gently leached without using acid.
“An ideal type of chelator compound is known as amino-polycarboxylates,” explains study co-author Ryuta Murase. “These are already used to remove toxic metals from solid waste. We found they were also very efficient at extracting REs from spent phosphors—especially yttrium and lanthanum.” Murase said EDTA was the best-performing chelator because it forms the strongest metal complexes. When plantetary ball-milling is added to the process, the larger surface area of the phosphors makes the rare earth metals easier to get at.
“We worked hard to optimize the process in every detail, including temperature, pH, milling speed, ball size, and other factors,” says corresponding author Hiroshi Hasegawa. “Recycling REs will be vital for sustainable technology, and we hope to show that it can be done cleanly and efficiently.”
Source: Kanazawa University