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REEs are used in a variety of ceramic applications, from glass sculptures to high-tech hybrid vehicle components (see Table 1). The ceramic and glass industry consumes approximately 10-15% or more of the REEs in commerce each year. Cerium and yttrium are the most commonly used elements of this group, which are used for glass polishing and ceramic manufacturing. REE applications include glass polishing compounds, optical glass, ultraviolet (UV)-resistant glass, X-ray imaging, thermal control mirrors, colorizers/decolorizers, capacitors, sensors, and scintillators.
Rare earth elements are becoming an increasingly expensive commodity due to reduced exports from China, the leading global supplier of REEs. However, suppliers of rare earth materials are poised to expand resources in the U.S., Canada, Australia and many other countries.
The costs of rare earth materials may not necessarily decrease with increasing supplies. Efforts to comply with environmental regulations in developed (and developing) nations may be a cost-controlling factor. Ceramic manufacturers can benefit from understanding the environmental lifecycle of their materials. A lifecycle analysis (LCA) can be employed to help implement more efficient processes so that vital resources are not wasted and to balance increased extraction rates while protecting the environment.
Mining LCAThe development of new rare earth ore deposits (including initial investigation, site permitting, mining and refining) requires several years to complete, as well as substantial capital investments.1 Historically, mining and processing activities have yielded a variety of environmental impacts, including soil, surface water, and groundwater contamination. These impacts are attributed to metals, acids, and other hazardous materials from mine tailings, wastewater impoundments, and ore processing facilities. They often require remedial actions to protect communities and/or the environment from exposure to hazardous materials.
Acid mine drainage is of particular concern from mining operations. Mine tailings often contain the mineral pyrite (FeS2), which, when exposed to air and water, forms an acidic solution that can impact surface water bodies and groundwater. This acidic solution often leaches arsenic and/or cyanide-both of which are hazardous to human health and the environment-out of surrounding rock formations.
Rare earth mining and processing is unique in that it is a complex multi-step process that is resource-intensive and may lead to unintended environmental impacts if performed improperly. As a result, new REE mining projects are likely to face intense scrutiny during the permitting process.
This has been the case at the Molycorp REE mine in Mountain Pass, Calif., the largest rare earth mine in the U.S., which had been closed since 2002 due to environmental concerns and increased production from China. The mine ultimately reopened this year, in part due to increasing REE prices and reduced supplies from China; its lengthy closure was also because the state of California only recently approved its environmental permits. It took Molycorp nearly a decade to complete the permitting process and install new environmental controls.
One way to understand how the increasing demand for REEs can impact the environment is to evaluate the sustainability of REE production using an LCA approach. Lifecycle analysis is an environmental management tool that takes a holistic approach to evaluating products and processes in an effort to avoid “problem shifting,” where a solution to one environmental problem impacts another part of a product’s lifecycle. In this way, the LCA process goes beyond environmental compliance in the traditional sense because it helps one industry (e.g., ceramic manufacturing) understand how activities along its entire supply chain (from resource extraction to disposal or reuse) impact the environment (see Figure 1).
For example, a recent LCA study evaluated the environmental impacts of REE production at the Bayan Obo mine in China.2 This study found that the production of REEs resulted in increased greenhouse gas (GHG) emissions, resource depletion and waste production, including low level radioactive waste. Typical rare earth deposits contain small amounts of thorium and uranium, resulting in low level radioactivity in the wastewater slurry and mine tailings.
While this example used an LCA approach to understand the environmental impacts associated with REE production, other studies have documented environmental impacts at former mining operations and facilities that formally processed REEs. For example, the previously discussed Bayan Obo mine has had documented releases of thorium, uranium, and heavy metals that have been linked to a possible increased incidence of illnesses in Baotou, China (population 1.7 million).
Releases of thorium, uranium, and heavy metals, as well as chlorinated solvents (e.g., volatile organic compounds or VOCs), have also been documented at REE mining and processing facilities in the U.S. and Malaysia. However, many of these releases occurred in the 1970s, ‘80s, and ‘90s. In the case of China, the releases occurred more recently (within the last decade), and environmental concerns are part of what fueled China’s decision to curb exports in 2010. As a result of the current state of knowledge regarding the environmental risks associated with REE mining and the advent of new treatment technologies, many of these concerns can be easily addressed at new and proposed REE mining and processing operations.
Commercial ConsiderationsFollowing extraction and processing, users of REEs must contend with a number of rules governing products in commerce. Environmental compliance does not stop once the pure rare earth oxide powders are shipped off to ceramic manufacturers. As REEs proliferate in the marketplace and in consumer products, the risk of human and environmental exposures is also more likely.
Unfortunately, little health hazard information exists for most rare earth metals. Regulators in Europe, the U.S., and other countries are requiring the disclosure of toxicity and hazard information for these materials. For example, the European Union’s Registration, Evaluation, Authorization, and Restriction of Chemical substances (REACH) regulation requires companies to provide comprehensive environmental characterizations based on import tonnage. Thus, requirements for reporting and examining environmental impacts for many chemical substances are expected to increase in the future.
Purified REEs typically come in powdered forms and, therefore, working with these materials can lead to the inhalation of metal dusts. Ceramic and glass manufacturers working with metal powders during product development typically implement occupational monitoring programs to ensure a safe working environment. Unfortunately, occupational standards for most rare earth compounds are lacking,3 and manufacturers have limited guidance to aid them. The only available REE occupational standard is for yttrium compounds (1 mg/m3 in air). Limited information suggests that exposure to high levels of REEs (particularly cerium) can affect the respiratory system. Therefore, ceramic manufacturers should critically evaluate their safety programs and limit exposure to metal dusts.
Finally, ceramic manufacturers must also ensure the safety of their products. Stricter public health laws are being developed in many U.S. states, and these laws will eventually apply to products incorporating REEs. For example, California’s Proposition 65 requires businesses to notify Californians about significant amounts of chemicals in the products they purchase, that may be present in their homes or workplaces, or that are released into the environment.
The U.S. Environmental Protection Agency (EPA) has a Green Chemistry Initiative whereby businesses are encouraged to evaluate chemical products and processes, and develop technologies or substitutes that reduce or eliminate the use or generation of hazardous substances. Lastly, the EPA and many state agencies are implementing electronic waste recycling programs to recover valuable metals and reduce the amount of wastes sent to landfills.
These laws can often be difficult to navigate and require manufacturers to reevaluate their environmental strategies. In addition, some states and foreign governments are requiring facilities to have ISO 9000-certified environmental management systems in place.
Multiple OpportunitiesREEs are key components for emerging “green” technologies. Components of hybrid and electric vehicles, solar panels, and wind turbines contain many ceramic components strengthened by these unique metals. The development of new rare earth resources in the U.S. and abroad is expected to alleviate current supply chain shortages.
The increased REE supply will hopefully contribute to the growing ceramic market sector. However, glass and ceramic manufacturers should continue to evaluate viable chemical substitutes, proper waste disposal techniques, and recycling programs to balance short-term supply shortages. The emerging green economy will have a bright future if ceramic manufacturers consider the environmental life cycle of REEs.
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References1. Long, K.R., Van Gosen, B.S., Foley, N.K., Cordier, D., “The Principal Rare Earth Elements Deposits of the United States-A summary of Domestic Deposits and a Global Perspective,” U.S. Geological Survey Scientific Investigations Report 2010-5220, 2010, http://pubs.usgs.gov/sir/2010/5220/.
2. Tharumarajah, A., Koltun, P., “Cradle to Gate Assessment of Environmental Impact of Rare Earth Metals,” presented at 7th Australian Conference on Life Cycle Assessment, Life Cycle Assessment: Revealing the Secrets of a Green Market, Melbourne, Australia, March 9, 2011.
3. American Conference of Governmental Industrial Hygienists (ACGIH), “2011 Guide to Occupational Exposure Values,” ACGIH Publication No. 0389, 2011.