Brief review of strategies to reduce environmental impact
Author: Dr. Caterina Tommaseo and Dr. Philipp Lengsfeld
Abstract
Rare earth elements are necessary for renewable technologies and electricity, and their demand is increasing with the ecological and energy transition. The ecological transition needs the rare earth elements in the production of electric vehicles and photovoltaic systems. However, the extraction of rare earth elements, which takes place with polluting methods, has an impact not only on territories and devastating effects on biodiversity but also necessitates strategic changes in the local communities, as well as in the geopolitical field. Rare earths are the main actors of the ecological transition, due to their diverse areas of application but also their specific properties such as ductility and malleability, versatility, and stable magnetism. On the other hand, they are complicated to be extracted and are associated at the same time with environmental pollution. Further important points of debate are the exploration of substitutes and recycling methods for management of demand/supply and reduction of environmental impact.
Rare Earth Elements’ identikit
Rare earth elements occupy an important place in the ecological transition, which are applied in renewable technologies, electronic vehicles, and batteries. Unfortunately, the extraction of rare earth elements has a significant impact on the environment due to polluting factors from the mining and processing. Therefore this article demonstrates the existing discrepancies in the generation of green energy and its environmental impact (Figure 1).
Figure 1: Overview of the rare earth elements` identikit for the ecological transition in correlation to renewable technology/green energy and in discrepancy to environmental/health protection concerning processing for their application. The exploration of substitutes, and recycle processes for the minimization of toxic/hazardous impact on environment/health affords challenges in the field of economy and research.
The term rare earths typically refers to a cluster of 17 rare earth elements (REEs). The cluster of 17 REEs comprise 15 lanthanides (atomic number 57-71), Scandium (atomic number 21), and Yttrium (atomic number 39). The 15 lanthanides are generally grouped depending on their atomic weights into “Light Rare Earth Elements” (LREEs) and “Heavy Rare Earth Elements” (HREEs), with Scandium (Sc) and Yttrium (Y) classified separately (UNCTAD 2014).
Traditionally, the majority of these REEs were used in the production of catalysts, polishing, ceramics, and phosphors. However, demand changed drastically in the 21st century, driven by the rapid growth of cleantech and high-tech-related applications such as magnets, metal alloys, electronics, and batteries. This means that they are easily found in our everyday lives from our energy-saving lamps to our smartphones. Futuristic applications of REE are in high-temperature superconductivity, safe storage, and transport of hydrogen for a post-hydrocarbon economy (U.S. Geological Survey, 2002). For applications of individual REEs, see (HEFA).
Application
REE are used in a range of electronic, optical, magnetic, and catalytic applications because of the specific and unique physical and chemical properties that the different REE possess (Adibi et al., 2014, Voncken, 2016) and are the main drivers of green energy and low-carbon sectors (Roskill, 2019). For example, neodymium (Nd) is an essential constituent of NdFeB high-strength permanent magnets that are often used in electric vehicles and wind turbines. The application in electric vehicles, which is currently experiencing significant growth, has contributed to an increased demand for REE. Today, the share of Nd being used in the glass industry is small at only 360 tons, compared to the 18,200 tons consumed in the magnet sector (Fishman et al., 2018).
A number of REE deposits have been identified around the world that could potentially fulfill the future demand outlook (Goodenough et al., 2017). China currently is the majority producer in all stages of the REE value chain. This combination of high economic importance, such as the need for Nd for the electric vehicle market, with an increased risk to supply disruption due to market concentration, has led many governments and organizations to classify REE as ‘critical’ materials (Graedel et al., 2015; Nassar et al., 2015; Pell et al., 2018). There is an additional incentive to develop production outside China to reduce production concentration.
The balance between supply and demand and the sources of supply can change quickly. In conclusion, criticality studies can be useful for decision-makers in policy and industry.
Environmental side effects of REE: mining and production
Mining and refining of REE are associated with serious environmental problems, such as soil and water contamination, human health, air pollution, etc. The environmental impact might also affect a sustainable production and stable supply chain of rare earths. The production of REE through mining, mineral processing, REE separation, and metal formation can cause environmental impacts. For example, mining can cause ecological destruction, pollution, and soil erosion (Liu and Diamond, 2005, Guo, 2012, Vahidi et al., 2016). Mining and mineral processing of REE can also generate large amounts of waste which may include high levels of radiation. The production of one ton of REE can produce 60,000m3 of waste gas that contains hydrochloric acid, 200m3 of acid-containing sewage water, and 1-1.4 tons of radioactive waste (L. Hayes-Labruto et al., 2013). The mineral processing and purification stages require high amounts of energy and are chemically intensive as well as producing significant amounts of waste products (Koltun and Tharumarajah, 2014).
Strategies for improvement: Substitutes
There are several pathways to reducing REE use in electric vehicle motors: (i) improving material efficiency in magnet production to obtain NdFeB magnets with less REE content but with similar performance; (ii) reducing the amount of NdFeB magnets in permanent-magnet synchronous motors; (iii) substituting permanent-magnet motors with REE-free motors. Improved material efficiency in magnet production can reduce REE content in permanent magnets but with similar performance characteristics. For example, material efficiency for neodymium and praseodymium may improve by up to 30% between 2015 to 2030 in a permanent magnet of equal magnetic strength and cost (Pavel et al., 2017)
As a result of research developments, Daimler indicates that the Dy content in permanent magnets in PHEV and HEV vehicles could significantly drop from 7.5–9% to approximately 5% in 2020 and afterwards to 2.5% (K. Ruland, Daimler AG, 2015). Terbium can replace dysprosium without losing performance, but due to its higher price and supply criticality issue it is not considered a convenient substitute.
Strategies for improvement: Recycle
REE recycling is currently very limited with less than 1% of all REE being recycled (Binnemans et al., 2013).
Recycling is mostly limited to permanent magnets and polishing compounds with a lesser amount from batteries and lamps (USGS, 2016). This is because REE are used in small amounts in the majority of their end-use applications, and there are challenges with the collection, extraction, and recovery of the constituent materials within end-products (Jowitt et al., 2018, Li et al., 2017). The permanent magnets used in modern technology (such as hard drives) usually consist of a neodymium-rich NdFeB alloy that might also contain smaller and varying amounts of Pr, Gd, Tb, Dy, and other metals. < 2 % of permanent magnets instead consist of a SmCo alloy free from other REE than Sm.
Traditional recovery methods for REE are based on e.g. hydrometallurgical, pyrometallurgical, and electrometallurgical techniques (Tsamis and Coyne, 2015).
The main challenge of REE recycling is usually the presence of contaminants in the feedstock. (Binnemans et al., 2013, Tsamis and Coyne, 2015). For example, electronic waste has a very complicated composition with numerous contaminants; common permanent magnets contain 72 weight% Fe, which in many suggested REE recovery processes cannot be recycled into a sellable product (Binnemans, 2013). In many cases, extensive pretreatment is required to extract a fraction from which REE can be recovered efficiently. (Schüler et al., 2011). Other challenges are deficiencies in the waste collection, technical difficulties such as separating neodymium magnets from the items that contain them, and a lack of incentives such as regulations or a sufficiently high and stable price level. (Binnemans et al., 2013, Schüler et al., 2011). Another problem is that many used goods containing REE are exported to developing countries, reducing available feedstock for the countries that have the technical infrastructure necessary for the recovery processes. (Schüler et al., 2011).
Conclusion
There is high demand for rare earth elements for the ecological and digital transition as renewable energies, electric vehicles, batteries increasingly take center stage. For this reason, the increasingly out of equilibrium rising demand/supply problem and the impact on the environment because of the mining and processing of rare earth elements needs to be improved focusing on the development of recycling processes and on processes and materials suitable to substitute rare earth elements.
The promotion of technology innovation on both the demand and production sides can enable more efficient use of materials, and allow material substitution, which brings substantial environmental and security benefits. Also funding research and development into new recycling technologies reduce the rapid growth of waste volumes and supports sustainability.
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