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A team led by Kanazawa University in Japan has developed a cleaner method for the recycling of several rare earths (REs) such as yttrium (Y) and europium (Eu) used as phosphors in fluorescent lamps (FLs).
End-of-life FLs are a potentially huge source of REs, but harsh and polluting processes are needed currently to extract these metals from the spent phosphors. As reported in Waste Management, instead of using acid extractants to dissolve the REs trapped in the spent lamps, the Kanazawa team turned to chelator chemistry.
Chelators—organic compounds containing elements such as N or O—bond to metals through electron donation. This allows them to gently leach out REs from the solid mass of a spent phosphor, without the need for strong acids.
To bolster the extraction rate, the team added a second ingredient to their process: mechano-chemical energy. Planetary ball-milling—i.e., grinding a solid into fine particles between layers of small, hard balls in a rotating chamber—was found to raise the yield of REs when performed during chelator treatment. This is because once milled the greater surface area of the pulverized phosphors provided easier access to the leachable metals within.