Concepts for the Extraction of Rare Earths from Spent Phosphors

"The rare earth elements (REE) are nowadays mainly used for permanent magnets, catalysts, hydrogen storage alloys in rechargeable batteries, for glasses, ceramics, and polishing agents. Other important areas of application are phosphors in different types of lamps (fluorescent tubes, energy-saving lamps, etc.). These lamps are often collected and treated at their end of life by disintegration and sorting. However, the obtained fine fractions comprise not only REE-containing phosphors but also small amounts of mercury and are therefore disposed till today in special landfills. Due to the enormous price increase of the rare earths during the last two years, a lot of activities started for extracting these elements from secondary resources such as for example phosphors. All recycling concepts for this task mainly work with hydrometallurgical methods. The large number of different compounds in phosphors with sometimes very different behaviors with respect to their solubility in aqueous phases forms a major challenge to achieve good yields as well as acceptable purities of the produced rare earth concentrates by a process with a reasonable number of operation steps. Therefore, this paper gives at first a brief overview about the compounds, used as phosphors and about existing concepts or investigations. It further describes our own process design and the results, obtained on laboratory scale. INTRODUCTIONThe rare earth elements (REE) have a central position in the industrialised world despite their marginal production volume in comparison to common metals such as aluminium, copper, zinc etc., because they are essential for many applications. They often cannot be substituted without a considerable loss on functionality and quality. This group of metals comprise the lanthanoids (f–block elements, lanthanum–lutetium) as well as scandium and yttrium.The estimated world mine production of REE amounted to 133,000 t rare earth oxide equivalent in 2010, whereat China accounted for 130,000 t or 98 % (Cordier, 2012). The European Union (EU-27) imported 23,013 t in 2008 to cover its demand. The figure 1 shows the fraction of the European member states in terms of the total imports of rare earth compounds from outside the EU-27 (Schüler, Buchert, Liu, Dittrich, & Merz, 2011)."