Low Carbon – High Damage? Renewable Energies and Rare Earth Elements

Achieving the goals of the Paris Climate Agreement limiting the global temperature increase to 1.5 °C will require massive investment in renewable energy. The transition to a decarbonized energy system will lead to a huge increase in demand for minerals, especially metals, rare earth elements (REE) and lithium, making the energy sector a major force in commodity markets. More mining is necessary than ever. The world mining production will ­increase the risk of high damages if the minerals will not be mined as sustainable as possible. Especially mining and processing REE to build permanent magnets for wind turbines and generators for electric vehicles are causing significant environmental challenges at the beginning of the supply chain. Mining REE is highly toxic. The ­source ­minerals of REE can contain the radioactive elements thorium and uranium, among others. And the more is mined the higher will be the volume of radioactive waste from th e separation of the elements. The paper describes the side effects of a rapidly growing industry that needs more sustainable business models to avoid risks or even disasters.

1  Introduction

In the net-zero emissions scenario, electricity becomes the new linchpin of the global energy system, providing more than half of total final consumption and two-thirds of useful energy by 2050. Total electricity generation expects to grow by 3.3 %/a to 2050, faster than global economic growth over the period. Annual capacity additions from all renewables quadruple from 290 GW in 2021 to around 1,200 GW in 2030. As renewables reach over 60 % of total generation in 2030, no new unabated coal-fired power plants are needed. Annual nuclear capacity additions to 2050 are almost four times the recent historical average (1).

An energy system powered by renewable energy technologies is fundamentally different from one powered by traditional hydrocarbon resources (2). More minerals and metals, e. g., are needed to build solar PV and wind farms than to build fossil fuel plants at same capacity. An onshore wind turbine park requires nine times more mineral resources than a gas-fired power plant while producing the same amount of energy. Electricity grids require huge amounts of copper and aluminum. According to the European Union’s Report on Critical Raw Materials for Strategic Technologies and Sectors, the demand for some rare earth metals used in permanent magnets for electric vehicles, digital technologies or wind generators could increase tenfold by 2050 (Figure 1) (3).

2  Risks of unsustainable mining for renewable energy

What emissions and waste are generated to produce renewable energy? It is necessary to look at the entire value chain, from extraction to production, including waste generation and recycling, in order to identify opportunities and risks of sustainable energy technologies. Inevitably, there is an environmental issue with renewable energy that has received little attention because most of its raw materials come from China, Myanmar, Vietnam, Malaysia, and Australia.

Unsustainable rare earth mining practices are in the spotlight for a long time, e. g., in Myanmar on the border to China (4). Myanmar has been able to increase annual production to an average of 24,000 t over the past five years (5). This production volume made Myanmar the world’s fourth-largest producer of rare earths.

Of particular interest in Myanmar are dysprosium and terbium, the two most valuable heavy rare earth metals (6). Their main area of application is high-performance permanent magnets, which are needed to manufacture motors and generators for electric vehicles and wind turbines.

The elements, extracted using a process known as in-situ leaching, are in high demand as China’s central government has stepped up its efforts to clean up the rare earths industry in recent years. Despite rising global demand, mines have been closed because of severely restricted regulations in Jiangxi province (Figure 2).

The process of in situ leaching is extremely critical from an environmental point of view. Large areas of soil are infiltrated with the leaching solution (ammonium sulphate). During the leaching process, the leaching solution, and an altered soil environment (low pH) can activate toxic heavy metals such as lead and zinc in the soil. Heavy metal contamination of soils is serious, and their accumulation has also been observed in surface and groundwater (7, 8). The use of environmentally friendly production methods, such as the use of biotechnological methods (bioleaching), unfortunately does not take place, although these alternatives are available (9).

Against the background that the recycling of rare earth ele­ments (REE) from end-of-life (EoL) products is less than 1 % on a global scale and can be described as “lost by design” (10, 11, 12), the questions are justified whether renewable forms of energy are truly sustainable and the term “clean energy production” is correct.

Like the use of nuclear energy in the past, there will be a shift in the problem areas in terms of time and space. Given that the production of REE increasingly generates more emissions and waste, this issue is becoming more and more relevant.

3  Rare earth elements and radioactivity

Renewable energy technologies will be an important growth driver for the REE industry. Global demand for rare earth permanent magnets for wind turbines and hybrid and electric vehicles continues to grow (Figure 3). Wind turbines require neodymium-iron-boron permanent magnets, which contain significant amounts of the REEs neodymium, praseodymium and dysprosium. For today’s wind turbines with permanent magnet generators, the average specific demand for neodymium is 0.2 t/MW (13). The demand for neodymium in wind turbines is forecast to be between 9,000 and 13,000 t in 2040 (14). In 2018, the global demand for neodymium for wind turbines was still 2,430 t (15).

Since 2011, the raw material criticality of rare earths has become particularly relevant, given the market turbulence and price developments and the resulting supply risk (12). In addition to market issues, other aspects must be considered, e. g., regarding the value of the deposits containing REE. Some of the deposits are described as high grade or high volume. However, this does not necessarily mean that they will be commercially successful.

One of the most controversial issues in REE is the presence of radioactivity in REE-bearing minerals, primarily thorium and uranium, although the REE themselves also have natural radioactive isotopes. Practically, the processing of monazite for rare earth production will produce a significant amount of thorium that needs to be managed safely to prevent the public concern and environmental impacts. According to an article published by the Chinese Rare Earth Society, the production of one ton of REE can also produce one ton of radioactive residue (16).

The content of naturally occurring radioactive material (NORM) in geological formations of REE can vary from insignificant to high concentrations, requiring legislation and special care and close monitoring during extraction. The mining, separation, treatment and disposal of radioactive materials can result in high additional costs as well as risks to health and the environment (17). In practice, to avoid regulations and liabilities, ore deposits with low concentrations of radioactive elements are preferred. Long term REE mining is in need for careful assessment to find a sustainable balance between viable mining and environmental (18).

In addition to the destruction of the natural environment, there are significant health impacts. The high levels of thorium oxide associated with REE have been known for some time (19, 20). The parent mineral monazite typically contains 3.5 to 10 % thorium oxide and 0.1 to 0.4 % uranium oxide. Thorium or thorium oxide should not be underestimated because of its radioactivity and toxicity. The ionizing radiation (decay type: α, γ) can cause considerable damage to the organism when inhaled. With a specific activity of approximately 7,150 Bq/g and a half-life T1/2 of 14.05 Ma, thorium oxide is no longer classified as low-level waste (LLW) but as intermediate-level waste (ILW) by the International Atomic Energy Agency (IAEA). Waste with a radioactivity of 1,010 to 1,015 Bq/m³ is called intermediate level waste or ILW.

4  Waste and emissions

World production of REE in 2021 was approximately 280,000 t (Figure 4). Although the volume of mining is still small compared to iron and steel (1.9 bn t of crude steel) and copper (around 20 Mt), there is a growing need to limit emissions from the production of these minerals, as they are also associated with increasing emission potentials (21, 22).

Reports on the waste management problems associated with the processing of rare earths at the Kuantan site of the Australian company Lynas Rare Earths Ltd. in Malaysia illustrate the importance of material flow management. Lynas claims to be an ethically and environmentally responsible producer of rare earths and the only producer of separated rare earths outside China (23).

The REE concentrates produced at Mount Weld in Western Australia are shipped to Kuantan/Malaysia. The Uranium and thorium grades of 11 ppm and 630 ppm, respectively, are in the upper range compared to other global deposits (24). There, processing continues by separating and segregating the REE concentrates from excess material. This process only generates more than 90,000 m³/a of radioactive waste. According to Lynas Rare Earth Ltd., the commercial use of the recycled waste, e. g., as building materials, will reduce the solid residues. However, there are concerns that recycled building materials may be contaminated or radioactive (25). Another consideration for the company is to dilute the waste to a thorium concentration of less than 500 ppm, which is the maximum concentration allowed by international standards for the material to be disposed of without restrictions. The plan is to process 220,000 t/a of waste using the “solution by dilution” approach (26). Environmental scientists see this as a poor solution.

Dumping is not an alternative for environmental reasons and to protect the population and workers (27). The creation of a toxic legacy site adds an unjustified burden to the current generation of people and future generations. Schüler et al. (28) cite the example of the Inner Mongolia Baotou Steel Union or China Northern Rare Earth mining company in their study, where REE are extracted as a by-product of iron ore. Data collected shows processing residues of 150 Mt (28). Additionally, there are approximnately 300 abandoned rare earth mines, 191 Mt of waste slag residues and tailings, and a contaminated forest area of 97 km² in Ganzhou/China. It should take the government 70 years and cost around 4.9 bn € to restore the environment (29).

Tailings ponds contain significant amounts of thorium, which, together with the dust generated during processing, can massively pollute groundwater and air (30). The resulting air pollution – especially due to dust – can be irritating to the skin, toxic or carcinogenic, depending on its physico-chemical composition. The extensive tailings ponds contain a variety of toxic chemicals and radioactive elements (Figure 5). These exposures can significantly increase the mortality rate from lung cancer. In the absence of precautions, toxic substances can leach into rivers, groundwater and soil, affecting the health of the local population. Consequences of such continuous poisoning include diabetes, osteoporosis and chest and respiratory problems (31).

5  Reuse of radioactive waste

For the reasons outlined above, the level of radioactive elements needs to be considered in detail, as it on the one hand has an impact on the environment and a direct influence on the inhabitants of the mining areas, and on the other hand requires responsible mining of the valuable minerals in an economically and environmentally sound manner. Due to the increasing transparency of value chains and the resulting stakeholder awareness of environmental and social issues, these aspects have the potential to become the strongest lever for more future sustainable business models in REE mining.

Current potential applications for thorium and thorium oxide are in welding electrodes, lamp construction, light bulb envelopes, alloys and optical lenses. A study by TH Georg Agricola University in Bochum/Germany has looked at sustainable uses for thorium and thorium oxide, with a view to achieving a true industrial symbiosis within the framework of company networks (32).

Currently, there is renewed interest in using thorium as a fuel source in nuclear technologies because thorium is more abundant than uranium (33). Thorium is considered a viable alternative to produce nuclear energy because it is an efficient fissile material that produces less unwanted waste than uranium. Government-supported projects on thorium-based nuclear power in China, India, Norway, USA and United Kingdom, e. g., could benefit from thorium extracted from REE processing (34, 35).

In addition, the thorium isotope 232 (90Th232) is on average 3.5 times more abundant than uranium in the rocks of the Earth’s crust. Global thorium resources are estimated at 6.4 Mt (5, 36). The world’s economically recoverable thorium is estimated at around 2.61 Mt, with Australia and the USA leading the way with 489,000 and 400,000 t respectively. The European economies Turkey and Norway have 344,000 and 132,000 t respectively of thorium (35).

Due to its – in comparison to uranium – short-lived radioactive waste (max. 300 years) and the high efficiency of thorium fuel elements, it has advantages over uranium (37). The use of thorium in the nuclear fuel cycle as a complement to the uranium/plutonium cycle also shows potential for improving the medium-term usage of nuclear energy and its side effects. However, its widespread use requires large quantities of uranium 233, too, which is only available when thorium is used with “classical” uranium/plutonium fuels (38).

In the longer term, the potential introduction of advanced reactor systems could provide an opportunity to realize the full benefits of a closed thorium and uranium 233 fuel cycle in dedicated breeder reactors currently at the design study stage.

Nuclear power is another low-carbon form of energy, alongside the renewable forms of wind, solar and hydro. A complete switch to renewable energy can only be achieved with sufficient storage or back-up capacity. Life cycle assessments show that the CO₂eq emissions of nuclear and wind energy over the entire life cycle are a factor of 5 lower than those of gas energy (39).

According to a comparative study to determine the CO₂ emissions of the most common types of power plant a coal-fired power plant emits approximately 950 g/kWh of CO₂, while a nuclear power plant emits approximately 30 g/kWh. According to the source, not only the operation, but also the entire life cycle of the plants, including all production steps, was considered (40). Further studies show that the overall radiation exposure from the use of the rare earth metals neodymium and praseodymium in wind turbines is lower to much lower than that from nuclear power (41) but it is still significant and cannot be ignored in the “political arena”.

Using thorium as a source material, reactors could be built to meet future energy needs. High potential is attributed to nuclear energy production with so-called “Generation IV” reactor concepts, in particular the liquid salt reactor or molten salt reactor (MSR) technologies (42, 43). Innovations in reactor technology promise lower costs, improved passive safety, faster construction times, smaller absolute size, more flexible siting and the ability to use nuclear waste as fuel. However, these designs are less proven and supply chains for many of their components have not yet been developed (43). However, the future development of world energy requirements could open up the possibility of realizing the processing and marketing of thorium, especially for smaller MSR reactor applications, in a strategic time horizon (44).

6  Discussion and summary

It can be assumed that the use of renewable energy will enable more environmentally friendly energy production through decarbonization, which is also urgently needed in view of population growth.

The rapid development of today’s society, accompanied by an increasing demand for energy and environmentally friendly high technology, requires ever greater access to REEs. As the demand for these elements increases, so does the amount of waste, by-products and residues generated during the various stages of their production. All of this leads to increasing pollution of the environment and all its components. As a result, elevated concentrations of uranium and thorium have been detected in air, water and biota.

However, the demand for a substantial contribution to climate protection by the EU based on renewable energy technologies is only possible if the raw materials, in this specific case rare earths, are mined responsibly and their by-products are used. Key challenges for responsible mining include growing waste issues, managing environmental externalities, integrating technological innovation and providing net social benefits to project affected communities. The use of environmentally sound production methods, the fulfilment of all recultivation tasks as an integral part of mining and the consideration and reduction of indirect costs/externalities is a compelling necessity (45, 46). Internalizing costs of harmful effects will be an incentive for the mining industry to improve its sustainability performance.

The permanent stock or the renewal and the development of wealth in a closed system with limited availability of resources is made possible by the circular economy through an economic approach in which the materials and energy used are not removed from the economic process as residues or waste but are fed back into the production or consumption process (47, 48).

The reuse of thorium, which is a by-product of REE production, should be considered for this reason a necessary option for the future. In addition to the deposit and the resulting opportunities for long-term primary energy production independent of solar and wind, thorium has the potential to increase the fuel content for the nuclear chain reaction, thus reducing the amount of waste for the same amount of energy produced compared to uranium. The demand for a clean, safe and affordable source of nuclear energy will influence the growth of the thorium market (49). The thorium market is expected to grow at a compound annual rate of 4 % from 2021 to 2028.

As described above, thorium can be successfully returned to the economic cycle. If this does not happen, if the (radioactive) waste is not used but diluted, the intended environmental objectives will not be achieved. Utilization should take place under the aspect of energy and resource efficiency. A circular approach, circular business models could directly meet two environmental objectives of the EU: pollution prevention and control and the transition to a circular economy.