This Review provides an overview of valuable metals, the supply of which has been classified as critical for Europe. Starting with a description of the current state of the art, novel approaches for their recovery from primary resources are presented as well as recycling processes. The focus lies on developments since 2005. Chemistry strategies which are used in metal recovery are summarized on the basis of the individual types of deposit and mineral. In addition, the economic importance as well as utilization of the metals is outlined.
Durch die Entsorgung quecksilberhaltiger Leuchtstoffe werden dem Wertstoffkreislauf jedes Jahr große Mengen an Seltenen Erden entzogen. Zur Rückgewinnung dieser Wertstoffe wurde die Feststoffchlorierung mit NH 4 Cl untersucht. Dies ist eine Aufschlussmethode abseits nasschemischer oder pyrometallurgischer Verfahren. Die betrachteten, teils Hg-haltigen Leuchtstoffmischungen enthielten neben La, Ce, Gd und Tb mit geringeren Elementgehalten vor allem Y und Eu. Durch NH 4 Cl-Zugabe und Erhitzen bis zur Zersetzungstemperatur des NH 4 Cl wurden Y und Eu in einer Sublimationsapparatur mit hohen Ausbeuten selektiv aufgeschlossen. Die Abhängigkeit des Aufschlussgrades und der Selektivität vom NH 4 Cl/ Leuchtstoffmischung-Verhältnis und der Temperatur wurden systematisch untersucht.Solid state chlorination with NH 4 Cl comprises a method for rare earth recycling apart from pyro-or hydrometallurgical strategies. The examined partially Hg-containing fluorescent lamp scraps are rich in rare earths like La, Ce, Tb and Gd, but especially in Y and Eu. By mixing with NH 4 Cl and heating up to NH 4 Cl decomposition temperature in a sublimation reactor, Y and Eu could be transferred selectively into their respective metal chlorides with high yields. The yield and selectivity depend on temperature and the ratio of NH 4 Cl to fluorescent lamp scraps, which were varied systematically.
Any development of an effective process for rare earth (RE) recycling has become more and more challenging, especially in recent years. Since 2011, when commodity prices of REs had met their all-time maximum, prices have dropped rapidly by more than 90 %. An economic process able to offset these fluctuations has to take unconventional methods into account beside well-known strategies like acid/basic leaching or solvent extraction. The solid-state chlorination provides such an unconventional method for mobilizing RE elements from waste streams. Instead of hydrochloric acid this kind of chlorination decomposes NH4Cl thermally to release up to 400 °C hot HCl gas. After cooling the resulting solid metal chlorides may be easily dissolved in pH-adjusted water. Without producing strongly acidic wastes and with NH4Cl as cheap source for hydrogen chloride, solid-state chlorination provides various advantages in terms of costs and disposal. In the course of the SepSELSA project this method was examined, adjusted and optimized for RE recycling from fluorescent lamp scraps as well as Fe14Nd2B magnets. Thereby many surprising influences and trends required various analytic methods to examine the reasons and special mechanisms behind them.
Dieser Aufsatz gibt einen Überblick über Wertmetalle, deren Versorgungslage für Europa als kritisch eingestuft wird. Aufbauend auf einer Darstellung des Stands der Technik werden neue Ansätze, vornehmlich seit 2005, zur Gewinnung aus Primärrohstoffen vorgestellt und die Recyclingverfahren diskutiert. Ausgehend von den jeweiligen Lagerstätten sowie der Mineralchemie wird aufgezeigt, welche Strategien zur Gewinnung der Metalle verfolgt werden. Außerdem wird auf die wirtschaftliche Bedeutung und Verwendung der Metalle eingegangen.
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