Binnemans, and 5 co-authors reported in 2013 that between 2000 and 2012, China has been producing more than 95% of the annual world supply of the rare-earth elements (REEs). Due to large and increasing domestic demands, China has introduced tight export quota for rare earths. These quota cause rare-earth supply risks outside China, but they also stimulate other countries to look for other rare-earth resources and to develop their own rare-earth industry. The shortage of rare earths stimulates the exploration for new rare-earth deposits, the development of new mines and the re-opening of older mines that had been closed in the past because of economic reasons. The supply risk of rare earths also provides a boost to the research on the recycling of rare earths from End-of-Life consumer goods. Up to now, rare-earth recycling (research) has focused on relatively small volumes of End-of-Life waste with a high REE content. However, rare-earths are also present in lower concentrations in a multitude of industrial residues.
This review discusses the possibilities to recover rare earths from residues such as pyrometallurgical slags, bauxite residue (red mud), phosphogypsum, mine tailings and waste water. All these waste streams have in common that they only have low REE concentrations, but are available in very large volumes. This implies that these industrial waste streams could provide significant amounts of rare earths, provided efficient recycling flow sheets can be developed.
The rare earths or rare-earth elements (REEs) are a group of 17 chemically similar metallic elements (15 lanthanides, plus scandium and yttrium). They are becoming
increasingly important in the transition to a low-carbon, circular economy, considering their essential role in permanent magnets, lamp phosphors, rechargeable nickel metal hydride batteries, catalysts and other green economic applications. The increasing popularity of hybrid and electric cars, wind turbines and compact fluorescent lamps is causing an increase in the demand and price of REEs.
The European Commission considers the REEs as the most critical raw materials group, with the highest supply risk. According to the medium-term criticality matrix
of the U.S. Department of Energy (DOE), the five most critical REEs are neodymium (Nd), europium (Eu), terbium (Tb), dysprosium (Dy) and yttrium (Y). China is presently producing more than 90% of all rare earths, although this country possesses less than 40% of the proven reserves. Due to large and increasing domestic demands, China tightened its REE export quota from 50145 tonnes in 2009 to only 31,130 tonnes in 2012. These export quota may cause serious problems for REE users outside of China, and, hence, also for the development of a more sustainable, low-carbon circular economy.
To tackle the REE supply challenge, a threefold approach can be proposed. A first component of this strategy is to substitute critical rare earths by less critical metals.
Secondly, the REE supply risk can be mitigated by investing in sustainable primary mining from old or new REE deposits. Mining companies are now actively seeking for
new exploitable rare-earth deposits and old mines are being reopened.
A good example is the Mountain Pass Mine in California, which restarted production in 2012. However, because of the absence of economic and/or operational primary deposits on their territory, many countries will have to invest in technospheric mining. Jones and co-workers distinguish between (1) direct recycling of pre-consumer
manufacturing REE scrap/residues; (2) urban mining of post-consumer (often complex multi-material) End-of-Life products; (3) landfill mining of historic (and future) urban and industrial waste residues containing REEs. Direct recycling and urban mining are focusing on resources with a very high content of rare earths, but the total volumes accessible to recycling are relatively low. The most interesting sources of rare earths for recycling are permanent magnets, nickel metal hydride batteries and lamp phosphors. Despite the existence of a vast literature dealing with (mostly lab-scale) research efforts on REE recycling, less than 1% of the REEs were being recycled in 2011. This is mainly due to inefficient collection, technological difficulties and a lack of incentives. Compared with the primary extraction of REEs from ores, the recovery of REEs via technospheric mining has the advantage that there are no issues with radioactive thorium and that the composition of the obtained REE concentrate is less complex. For instance, lamp phosphors contain mainly Eu, Tb, Y, Ce, La, but are devoid of Nd, Pr and Dy.
Binnemans, et al. (2013) recently published an overview of the state-of-the art of recycling of rare earths, focusing on End-of-Life material streams. On the other hand, much less attention has been paid to industrial waste residues containing rare earths (both present in historic landfills and being freshly produced). These industrial waste residues contain much lower concentrations of REEs than the End-of-Life consumer goods that are considered for recycling via urban mining activities. However, the volumes of these residues are enormous so that the total amounts of REEs locked in these residues are also very large. This review paper gives on overview of the possibilities to recover rare earths from important industrial waste streams, i.e. metallurgical slags, bauxite residue (red mud), phosphogypsum, mine tailings, and waste-water streams.
Managed & Built by I2M Consulting, LLC | © 2010-
