Recover rare earths from old fluorescent tubes

By Wolfgang Kempkens

You are special, discarded fluorescent tubes. They contain rare recyclables, including the coveted rare earths. Now researchers at the Technical University of Freiberg have developed a method, that these raw materials recovered - and is profitable.

Rare earth to their name in honor, at least as "rare" refers to. Its value is high and easily influenced. China, the 90 Percent of Promotes rare earths, has already threatened to, to curb the export. You can find the rare metals are used in displays, Fluorescent, Mobile phones, Permanent magnets, Batteries and even polishes.

Discarded appliances are indeed recycled. But the minute amounts of rare earths previously could not recover themselves. Often only small amounts are installed, whose recovery is too complex and therefore too expensive.

Chemists at the Technische Universität Bergakademie Freiberg have now developed a method, the smallest amounts of rare earths and other raw materials can be recovered as mercury. The importance of the method lies in the fact, "That we reappraise it easy to track all phosphors regardless of their Seltenerdgehalten", so Professor Martin Bertau, Director of the Institute for Technical Chemistry, who led the research. "We isolate the metals in pure form, - without countless plates, as is the case in classical rare earth treatment. "

From some of tonnes of waste a few kilograms of recyclables

Without separation stages is not, however,. The internal coating of fluorescent tubes, which generate light during operation, be washed with hydrochloric acid. The result is a kind of porridge, Called slurry, the earth beside the coveted rare yttrium, Contains gadolinium and europium, impurities such as calcium and barium.

To separate the latter, the slurry is mixed with sulfuric acid. Here is calcium to form gypsum, Barium to barite. Now the rare earths are in the hydrochloric acid only dissolved. Which are separated by diffusion dialysis of the acid. This part consists of a membrane, lets through only the rare earths. For other molecules it acts as a barrier. Lastly, the metals, present as oxides, separate.

The special feature of development in Freiberg: The researchers have made the step from the laboratory out into a larger system. A larger plant has the TU together with the company FNE disposal services Freiberg and NARVA light sources GmbH & Co. Developed KG. The system is designed for the processing of some metric tons per year production waste. Rare earths are obtained on a kilogram range. "In fact, it is one of the few methods, who have made the leap from the laboratory to industrial production, while at the same time economically ", said Professor. Bertau.

First production waste is recycled by the lamp manufacturer Narva medium Saxon town of Brand-Erbisdorf, covering the entire range, from classical fluorescent tube to light emitting diode lamp. The precious Committee moves to the FNE disposal services Freiberg where it is processed in the new facility. The rare-earth, but also metals such as mercury, be recovered unmixed. Narva puts, after they have been cleaned in a further service provider, back into production.

Positive results despite price drop

Despite the current fall in prices for rare earths, the method is viable. "We have a positive balance", says Martin Seifert, PhD student at Bertau and head of the FNE resorts workup. Europium about costs around 600 Euros per kilogram. 2012 were still good 3000 Euro.

http://www.ingenieur.de/Fachbereiche/Umwelt-Recyclingtechnik/Seltene-Erden-alten-Leuchtstoffroehren-zurueckgewinnen

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