Critical mass - rare earth elements

Materials World magazine
,
1 Jan 2012

There are constant warnings about the risks of exhausting supply of vital resources, including the impact on our way of life. Professor Animesh Jha, from the Institute for Materials Research at the University of Leeds, UK, examines the sources of rare earth elements and the research driving their use in emerging technologies.

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Rare earth elements are identified in the periodic table by the lanthanide series of 15 elements, starting with lanthanum and finishing with lutetium. Two more prelanthanide elements, yittrium and scandium are often included with the 15 lanthanide elements, thus the series is made up of 17 elements. The most stable valance state for these elements is (3+) which is characterised by their electronic structure. However the less dominant (4+) state is also observed in cerium, praseodymium, and terbium, all found in natural compounds and, the 2+ states in europium, samarium, and thulium under controlled oxidising conditions.

The identification of rare earth elements (REEs) on the critical list of materials affects the supply chain and may adversely affect the world’s desire for developing cleaner and more energy efficient electronic devices, including: displays, computer hard drives, wind turbines, fuel cells, hydrogen storage materials, efficient high-power lasers and amplifiers for materials processing and optical communication systems.

The REE supply chain affects three main sectors of the world economy – energy, health, and digital. Since the energy and digital economies are directly affected by the supply chain, there is also an impact on the natural and built environments, and therefore on long-term climate change. Scientifically the 17 REE elements are some of the most inspiring as a result of a rather unusual combination of properties, manifested by their electronic and nuclear structures. And this explains why they have found a multitude of applications in technology.

According to data supplier United Business Media (UBM), ‘The global demand for rare earths grew at five per cent per year between 2005 and 2010, although the market shrank in 2009 in line with the global economic downturn, which had a marked negative impact on demand in the rest of the world. Estimated total demand in 2010 was 125,000 tonnes of rare earth oxides.’ The global recession has led to a fall in demand for rare earth oxides (REOs), however it is only a short-term outlook. The climate change targets for CO2 reduction continue to affect both industry and government policy. This is especially true of policies for the adoption and implementation of REO-based technologies for the built environment and national infrastructure, such as transport and energy supply.

Consequently, the demand for REOs will rise again together with the new suppliers from outside China – the current major player in the supply of these elements. This is essential for reaching equilibrium in the supply and demand cycles of REOs for emerging technologies. The recent fall in the price of neodymium is attributed to the new suppliers in the market. With the world’s major and emerging economies yearning for clean, renewable means of energy production, rare earth materials will continue to dominate the debate both in scientific and government circles.

Table 1: A comparison of various rare earth
oxides in US$/kg since 2008 outside China. The price for inside China is
for 2011, which shows the need for driving the green energy agenda


Resources and energy competition

Finding new sources of REEs and recycling them are important for a sustainable economy. Research suggests that the massive monazite (AlPO3) crystals, which are a good source of REEs and commonly found in pegmatite rock, are few and far between. Wherever rich monazite is found in pegmatite deposits, the weathering leads to placer deposits (natural concentrations of heavy minerals caused by gravity moving the particles) that may be in the form of beach sands for REE supply.

The other common mineral types from where REEs can be formed are carbonates and fluorinated carbonates in the form of bastnasite. Introduction of water, carbonate, or CO2 derived from a garnet source (a group of more than ten different minerals of similar chemical composition) can significantly enrich the light REEs over the heavy REEs in metasomatised mantle (chemically altered mantle through hydro-thermal circulation). These garnets are known to form under supercritical conditions of water and CO2, as revealed recently from the geological mapping of the mid- Pacific ocean bed by Yasuhiro Kato, a geo-system engineer at the University of Tokyo. Bastnasite is one of the main constituent minerals found in Baiyun Obo, Inner Mongolia. Recent reports from the US and British Geological Surveys document mineral resources in the USA and other areas.

Exploration at Mountain Pass in California, run by Moly Corp, is one of largest sites outside China. It used to be one of the oldest and largest sites in the world for REO mining before 1985, when it was mothballed by shifting operations to China. A comparison of China’s domestic price for REOs against prices elsewhere in November 2011 shows the demand for REOs for clean energy generation inside China is likely to create an uncompetitive scenario for the rest of the world. From the late 1980s until early 1990s, India was also exporting REOs, which stopped when the potential importance of the materials for rare earth metals (REM) iron and samarium cobalt magnets was realised. Rare earth magnets were discovered in the early part of 1987 by General Motors in the USA and Sumitomo Metals in Japan.

In view of the limited resources in Western Europe, the REO supply situation appears to be more focused on recycling, especially from materials at the end of life. Although recycling REOs is an important area for growing new types of commercial activities, it is unlikely to meet the rising demands in the energy and digital sectors. Present supply chain scenarios suggest that if Europe focuses on research and development for cleaner technology based on REEs, there might be a joint opportunity to work with major mining companies outside China for creating healthy competition and industry.

The UK situation

The report on critical materials for the energy sector by the Joint Research Council within the EU identifies the neodymium and dysprosium metals as essential for meeting the demand for wind turbines and hybrid cars, and hydrogen storage. Consideration for catalytic converters for auto-motives and fuel cell devices is likely to increase demands for cerium oxide as well, which is not identified in the critical materials list. Similarly materials such as the oxides of europium and terbium, essential for solid-state lighting, are missing from the list.

Development of research and development capability in the UK and the rest of western Europe has already started. In the UK, the Less Common Metals Company in Birkenhead is a major rare earth metal producer. Recently, the Chemistry, Materials, and Environmental Sustainability Knowledge Transfer Networks have also identified the need to create research and development capabilities and new opportunities for business regarding REEs. Key features of emerging trends in REE research in the UK are:

  • A long history of hydrogen storage and magnetic materials research at the University of Birmingham, led by Emeritus Professor Rex Harris, has now been successfully used in recycling neodymium magnets through a TSB project.
  • Pioneering research by Professor Derek Fray on cathodic dissociation of metal oxides for electrowinning of metals at the University of Cambridge has led to commercial exploitation by Metalysis Limited in Rotherham, Yorkshire. The highly desirable electrochemical technique is for further purification of the REO and REM mixture into component metals or alloys, including the production of RE magnetic alloys.


Bright future?

It is impossible to contemplate a future without rare earth elements. Although there is a research initiative within the EU that is inviting bids for basic research and development in extending knowledge, which aims to supersede the performance of REO- and metal-based devices. If successful, it will be a disruptive technology with a time-scale of market entry for such technologies of at least 10 years. In the meantime the new and emerging REO must progress within the EU to support industry.

Geological survey and exploration must continue within the EU and with trading partners for developing novel means of mining and mineral beneficiation. Exploration in the mid-Pacific has revealed an abundance of yittrium-rich, light and heavy REEs in 100–1,500ppm concentrations, making the resource attractive for deep-sea mining, which carries significant risk and expense. Such exploration carries incalculable environment cost, concerning the use of energy intensive equipment and disturbance of the sea bed that is likely to release trapped greenhouse gases. In the past deep-sea mining of sea nodules for manganese and nickel has never been commercially viable.

The only viable option that remains is to continue exploring terrestrial sites for REEs, recycle, and develop new scientific understanding employing nano-science for economising the use of such sought after materials. A philosophy that must be embraced for conservation of rare earch oxides and metals comes from American physicist Richard Feynmann, who says, ‘there is plenty at the bottom’.

Further information

Professor Animesh Jha. Tel: + 44 113 343 2342. Email: a.jha@leeds.ac.uk Thanks to EPSRC and DTI, and the Millennium Inorganic Chemicals for their support. Also the PhD Studentship from the Chemistry and Environmental Sustainability KTN.