The rare earth metals are a group of 17 silvery-white, metallic elements consisting of the 15-element Lanthanide series on the periodic table plus scandium and yttrium. Although they share very similar chemical properties, they have unique magnetic, catalytic and optical characteristics that make them essential for improving performance, including speed, efficiency, durability and thermal stability, in magnetic, catalytic, electronic, energy and other applications.
Despite their name, the rare earth elements are not scarce. However, they are rarely found in concentrated deposits; rather, they are usually dispersed and mixed in low concentrations with other elements, making their extraction difficult and costly.
The most abundant rare earth metal is cerium. It ranks as the 25th most abundant element in the earth's crust, making it roughly as common as copper. Among its diverse applications are catalysts, glass polishing powders and metal alloys.
The most used rare earth element is neodymium, because it makes possible the most powerful permanent magnets, thus enabling a variety of products to be made smaller, lighter, and more energy-efficient. Permanent magnets are the largest application for rare earth elements as a whole in terms of both weight and value, at about 30 percent and 41 percent, respectively.
The second largest application is catalysts, at about 17 percent of total weight, followed by polishing powders, metallurgical uses, glass and ceramics production, lighting and alloys. The main rare earth elements used as catalysts are cerium and lanthanum, which are favored not only because of their excellent performance but also because they are more abundant and less expensive than other rare earth elements. Rare earth-based catalysts are used primarily for automobile emission control, petrochemical refining, industrial waste gas purification, and improving the performance of fuel cells.
The automobile industry, particularly the electric vehicle sector, is a large and rapidly growing user of rare earth metals. The share of total rare earth production used in automobiles is 20 to 30 percent, mostly for permanent magnets for electric and hybrid vehicle motors and also for catalytic converters for emissions control. The average electric vehicle uses approximately 0.5 kg of rare earth elements, about double that of a traditional fossil fuel vehicle.
The mining and refining of rare earth metals have substantial environmental effects, including long-term damage to ecosystems and public health. They are difficult, dangerous, costly and destructive, particularly for the heaviest ones (i.e., dysprosium, terbium and yttrium) for several reasons. (1) The ores are widely dispersed and often occur in deposits with complex geology, including being mixed together in low concentrations with other minerals. (2) Large, open-pit mines are often required. (3) The ores are chemically highly stable and thus require multiple, energy-intensive stages of chemical processing to break them down. (4) The ores frequently contain radioactive elements, mainly thorium and uranium. These factors typically result in contamination of the soil, surface water and groundwater with toxic heavy metals, acids, wastewater and radioactive materials, and also contribute to air pollution with the release of airborne dust and waste gases.
The mining and refining as well as the consequent damage is primarily concentrated in developing countries and in those with weaker environmental regulation and enforcement, including Myanmar, Madagascar, Malaysia and China. That is, it is largely a transfer of environmental damage from the wealthier nations to the less developed nations.
There are several ways to reduce the destructive environmental and health effects caused by the mining and refining of rare earth elements. Because making these activities safer remains challenging, an alternative approach is to reduce the use of rare earth elements. This can be accomplished to some extent by improving the performance of alternative materials and technologies, such as magnets that do not contain rare earth metals and electric motors that do not use magnets, for example, using induction motors instead of permanent magnet motors.
It can also be accomplished by decreasing the production and use of products which contain them. Automobiles are a particularly good example because there are already very strong environmental and public health reasons to reduce their production and use. These reasons include their major contributions to greenhouse gas emissions, air pollution, urban sprawl, habitat loss, traffic accidents and metabolic diseases.