Development of a Continuous Process Chain for Selective Recovery and Purification of Rare Metals

Solar cells, liquid crystal displays (LCDs) and light-emitting diodes (LEDs) have become more and more important in recent decades. Crucial components of such electronic devices include rare metals (e.g., indium and gallium), which are only available in limited quantities. In order to meet their rising demand in the coming years, recycling processes, especially those that enable selective recovery of the individual components, are steadily gaining in importance. One conceivable method is particle-loaded solvent extraction followed by mechanical processing. Therefore, we first investigated the possibility of recovering individual particle fractions from a multicomponent mixture on the basis of the surface properties. Both UV-Vis spectroscopy and small-angle X-ray scattering (WAXS) were used for evaluation. The conducted experiments showed, among other things, that the indium oxide content increased from 50% to 99% in a binary system and from 33% to 94% in a ternary compound. In addition, the purification of the separated particles was examined in detail. Using UV-Vis spectrometry, it was found that permeation washing of filter cakes is suitable for removing impurities and retrieving most of the solvent used. Based on the results of the conducted laboratory tests, we finally developed a concept for the continuous and selective recovery of rare metals.