Perspectives for rare-earth recycling

Abstract

1. Abstract The economic evaluation is fundamental in the recycling industry. For example, aluminium is recycled in large scale, because it is a profitable business. The viability of aluminium recycling depends strongly on the cost of electric energy. For example, if the electric energy is expensive, this increases the profitability of aluminium recycling. In the case of rare-earths, recycling is possible, but the economic side can not be neglected. First, it is necessary to understand the main applications of rare-earths and the rare-earths demand. The rare-earth market is now driven by iron rare-earth magnets. Neodymium, Praseodymium, and alloying elements as Terbium, Dysprosium and Holmium have high cost, associated to high demand. Tb, Dy and Ho are alloying elements added to increase the temperature of operation of the magnets. Magnets use rare-earths as alloying metals, and the purity can be of 99 or 99.5%. Thus, the purity of rare-earths in magnets is well below the purity of oxides used as dopants in lasers. The lasers and luminescent phosphor industry many times request oxides with purities of four 9 level (99.99%) or even six nines (99.9999%). Lanthanum is used in large scale by oil cracking industry, for stabilization of zeolites. The lanthanum can be recycled by the oil industry. But with lanthanum oxide price near 2 US/kg,thisproceduremaynotbeeconomicallyinterestingAveryrelevantapplicationofrare−earthssincethe1960shasbeenluminescentphosphors.Europiumhadbeenthemostexpensiverare−earthforlongtime,butsince2015thepriceofEuropiumdecreasedsignificantly.TheRGBsystemhasbeenreplacedbyblueLEDcoupledbyyellowphosphor.Somerare−earthsasEuropiumandTerbiumwereusedinPlasmaoldTVsandalsoinCFLlightbulbs.TheRGBsystemwasusedforproducingwhitelight.TheredandbluecolorsusedtobeproducedwithEuropiumbasedphosphorsandthegreencolorwithterbiumbasedphosphors.ButrecyclingofrecentLEDTVsmaynotbeinteresting,andthesameforrecentLEDlightbulbs.TherecyclingofoldRGBsystemmaynotbeprofitablebecausethelowpriceofEuropiumnow,around60US/kg, this procedure may not be economically interesting A very relevant application of rare-earths since the 1960s has been luminescent phosphors. Europium had been the most expensive rare-earth for long time, but since 2015 the price of Europium decreased significantly. The RGB system has been replaced by blue LED coupled by yellow phosphor. Some rare-earths as Europium and Terbium were used in Plasma old TVs and also in CFL lightbulbs. The RGB system was used for producing white light. The red and blue colors used to be produced with Europium based phosphors and the green color with terbium based phosphors. But recycling of recent LED TVs may not be interesting, and the same for recent LED lightbulbs. The recycling of old RGB system may not be profitable because the low price of Europium now, around 60 US/kg in May 2018. Recycling of permanent magnet is a possibility. The best way is re-melting the magnets (not recovering the oxide again). Energy is spent in the rare earth reduction, and this energy is lost if the magnets were converted in rare-earth oxides. Recycling of magnets used in wind turbines is easy. However, many magnets are used in very small motors of hard disks, or speakers, as for example speakers of cell phones. These small magnets need to be separated from the rest. The cost of dismantling need to be considered when recycling small magnets. Thus, there are many considerations to determine the viability of rare-earth recycling. Marcos Flavio de Campos-Federal Fluminense University-Volta Redonda RJ-BRAZIL）