Module 24 Mineral Resources and Geology

Module 25 Weathering and Soil Science

Many people in the environmental science community believe that hybrid electric vehicles (HEV) and all-electric vehicles are some of the most exciting innovations of the last decade. Cars that run on electric power or on a combination of electricity and gasoline are much more efficient in their use of fuel than similarly sized internal combustion (IC) automobiles. Some of these cars use no gasoline at all, while others are able to run as much as twice the distance as a conventional IC car on the same amount of gasoline.

Although HEV and all-electric vehicles reduce our consumption of liquid fossil fuels, they do come with environmental trade offs. The construction of HEV vehicles uses scarce metals, including neodymium, lithium, and lanthanum. Neodymium is needed to form the magnets used in the electric motors, and lithium and lanthanum are used in the compact high-performance batteries the vehicles require. At present, there appears to be enough lanthanum available in the world to meet the demand of the Toyota Motor Corporation, which has manufactured more than 3 million Prius HEV vehicles. Toyota obtains its lanthanum from China. There are also supplies of lanthanum in various geologic deposits in California, Australia, Bolivia, Canada, and elsewhere, but most of these deposits have not yet been developed for mining. Until this happens, some scientists believe that the production of HEVs and all-electric vehicles will eventually be limited by the availability of lanthanum.

In addition to the scarcity of metals needed to make HEV and all-electric vehicles, we have to consider how we acquire these metals. Wherever mining occurs, it has a number of environmental consequences. Material extraction leaves a landscape fragmented by holes, and road construction necessary for access to and from the mining site further alters the habitat. Erosion and water contamination are also common results of mining.

A typical Toyota Prius HEV uses approximately 1 kg (2.2 pounds) of neodymium and 10 kg (22 pounds) of lanthanum. Mining these elements involves pumping acids into deep boreholes to dissolve the surrounding rock and then removing the acids and resulting mineral slurry. Lithium is extracted from certain rocks, and lithium carbonate is extracted from brine pools and mineral springs adjacent to or under salt flats. Both extraction procedures are types of surface mining, which can have severe environmental impacts. The holes, open pits, and ground disturbance created by mining these minerals provide the opportunity for air and water to react with other minerals in the rock, such as sulfur, to form an acidic slurry. As this acid mine drainage flows over the land or underground toward rivers and streams, it dissolves metals and other elements. As a result, water near surface mining operations is highly acidic—sometimes with a pH of 2.5 or lower. It may also contain harmful levels of dissolved metals and minerals.

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Current HEV technology does represent a step forward in our search to reduce the use of fossil fuels. However, to make good decisions about the use of resources, we must have a full understanding of the costs and benefits.

Sources: M. Armand and J.-M. Tarascon, Building better batteries, Nature 451 (2008): 652–657; Anonymous, Rare earth metals may trigger trade wars, www.discovery.com, February 11, 2013.