Rare Earth Metal Recycling

Transcription

1 Rare Earth Metal Recycling Laura Meyer, Bert Bras, Member, IEEE REs consist of the fourteen lanthanide group metals, Scandium, and Yttrium and are critical for advanced technologies, green technologies, and defense technologies. Nearly 200 minerals contain >0.01% RE metals but only a dozen have high enough quantities to be economically extractable. In this article, we will review the need for rare earth recycling, options available to recycle rare earth metals, and the possibilities and difficulties of recycling rare earths on an industrial scale. Even though processes are available to extract RE metals from waste products, most of them are still at laboratory scale and very few examples exist where they have been applied in industrial size recycling settings. Because rare earths are used in small amounts, a key challenge is the lack of information about the amount of rare earth metals in products. Nevertheless, preliminary findings show that specialized rare earth recycling lines may be technically feasible, but not economically profitable unless a broader systems perspective is taken. Index Terms Mining Industry, Rare Earth Metals, Recycling, Waste Recovery 2010 [3]. In the second half of 2010 alone, China decreased export quotas by 72% and an additional 35% during the first rounds of 2011 permits [4]. The resulting supply and demand gap has opened a market which the international community is attempting to fill by accelerating the opening of additional mines. The supply and demand gap should also be filled by rare earth recycling enterprises. II. RARE EARTH DEPENDENCY CONCERNS A. United Sates Concerns and Governmental Response As seen in by the applications in Table I, REs are critical for the life style the developed world has grown accustomed and for future life style improvements. In the past RE s were not a major concern because they occur in such small percentages within products and the market prices were kept low by China s high export rates. The United States used to be one of the prominent rare earth producers but closed its mine due to environmental concerns and the difficulty of competing with China s rare earth prices. China began cornering the I. INTRODUCTION are Earth (RE) metals are critical to high technology R like computers and MRIs, green technology like energy efficient light bulbs and wind turbines, and defense technology like jet fighter engines and smart bombs, because of their unique chemical, magnetic, electrical, and luminescence characteristics. REs consist of the fourteen lanthanide group metals, Scandium, and Yttrium. The National Minerals Advisory Board, the National Academy of Science, the National Academy of Engineering, the National Research Council and the National Academy of Medicine all concluded that REs are critical to our nation s industrial interests [1]. In 2010 the United States was 100% import dependent on RE Oxides and 97% of the world s exports are from China [2]. In 2005 China started decreasing their rare earth exports, leading up to a 40% decrease in exports between 2009 and We gratefully acknowledge the support of the National Science Foundation under Grant No Materials Use: Science, Engineering, and Society (MUSES): Modeling Material Flows for Sustainable Industrial Systems for Urban Regions (SISFUR). Any opinions, finding and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the view of the United Sates government and/or the authors parent institutions. Ms. Laura Meyer is with the Sustainable Design and Manufacturing Lab at Georgia Institute of Technology, Atlanta, GA USA (phone: ; fax: ; lmeyer3@gatech.edu). Dr. Bert Bras is with the Sustainable Design and Manufacturing Lab at Georgia Institute of Technology, Atlanta, GA USA ( bert.bras@me.gatech.edu). market in the 90s, during which Deng Xiaoping compared China s rare earths to the Middle East s oil. Secretary of State Clinton proclaimed the Chinese export restrictions as a "wakeup call" for the world to seek additional sources of REs [6], [7]. With China s dramatic change in export policy in 2010, H.R was approved by the House of Representatives and if passed by the Senate would have established a research and development program in the DOE to assure long-term supply of RE metals. Between February 10 and April 15, 2011, six rare earth related bills were introduced in congress. Three of those focused on rare earths: H.R. 618: Rare Earths and

2 Critical Materials Revitalization Act of 2011, H.R. 1388: Rare Earths Supply Chain Technology and Resources Transformation Act of 2011, and H.R. 1314: Resource Assessment of Rare Earths Act of The 2011 National Defense Authorization Act mandates the Department of Defense to work towards improving their RE supply chain and to establish a domestic source of Nd-Fe-B magnets. The Department of Energy continues to address their dependency on rare earth elements as the work towards their second Critical Materials Strategy report which should be published in December B. Supply and Demand Gap In 2011 China has continued to enforce a strict export policy. China is working to consolidate mining efforts and eliminate illegal mines, which supplied 15,000-20,000 tons of RE metals [8]. Table II shows non-chinese s mines that as of March 2011 were at least in the pilot plant stage of development and plan to start selling REs on the market by For calculations, the Chinese mine export rates were based off the 2011 export quota and distributed among the mine production percents seen in 2010 [9], [10]. Even with assuming all ten mines successfully start commercial production by 2014 and that the Chinese mines continue to export at their 2011 rates, terbium falls over 50% short of the 2014 predicted demand of 600 tons [11]. This gap will need to be closed by finding substitute materials for rare earths, reduction of rare earths used in products, and by recycling. III. MINING FINANCIAL AND ENVIRONMENTAL COSTS Rare earth mining is financially and environmentally demanding. Ores must go through a concentration and separation process which can involve crushing, grinding, flotation, filter pressing, sulphation, heating, leaching, multiple separation processes, precipitation, filtration, and refining [11], [20]. In 2010, Molycorp predicted that after renovating their mining facilities their operations would produce ton/yr of CO emissions, tons/yr of VOC emissions, tons/yr in NO X emissions, and 2.24 tons/yr in SO X emissions [21]. In March 2011, Lynas predicted their construction and other capitol costs for the Mt. Weld mine to be $535.2 million in Australian dollars [11]. After construction is complete, Lynas s average rare earth oxide production cost will be $10 per kg, Australian dollars [22]. IV. URBAN MINING Urban mining, a form of recycling, is the process of extracting valuable resources, like REs, from waste. Rare earths are present in waste fluorescent lamps, catalysts, antilock brakes, NiMH batteries, motors, and other products that are used throughout urban regions. REs are almost 20% of a NiMH laptop battery [23] and compose approximately 98% of lighting phosphors [24]. In comparison, Mount Weld, who has the richest rare earth ore of any potential mines as of March 2011, is only 9.7% RE [25]. Mount Weld s Eu supply is thus only about 0.4% of the ore compared to the lighting phosphors which are 4.9% europium [24]. Ideally the portion of the application that contains the REs can be extracted, refurbished, and then reused for the same application. This transition towards a closed loop supply chain will keep the energy and transformations from prior processing within the product supply chain and thus potentially decrease cost and emissions during product production. A. RE Extraction Properties Another physical advantage to urban mining is the rare earth extraction process. Much of the difficulty of extracting RE metals from the earth occurs because they appear intermixed in ores. Extraction methods separate elements by the differences in their properties, which are minimal between rare earths. Some of these characteristics include: reactivity, electrical conductivity, and melting points along with ionic and strongly paramagnetic properties which are common for all REs; solubility and complex formation which only have very small differences between REs; and basicity and density which undergo size induced variations. The REs are essential for their unique chemical, magnetic, electrical, and luminescence characteristics, but the minute differences in characteristics between the rare earths make it difficult for them to be separate from each other. When rare earths are separated from waste products, they are intermixed with fewer rare earths and sometimes occur in higher concentrations than ores. There is also the possibility of eliminating the complications of extracting intermixed rare earths by extracting the mixture, then refurbishing the mixture to be placed back in its original supply chain. B. Extraction Methods RE recovery from waste products consists of three major steps: separation of the RE component from the source device, extraction of the RE metals from the RE component, and finally metallothermic reduction of the RE metals. RE components can be separated from their source device mechanically like neodymium magnets in cell phones or through leaching like phosphors in a lamp. Leaching uses a solvent to selectively dissolve one or more components [26], [27]. Both the leachette and the mechanically separated RE components will contain other elements in addition to the RE

3 metals, thus extraction and reduction steps are taken to obtain the individual RE metals. During the extraction steps, REs are separated as oxides, fluorides, salts, double salts, chlorides, hydroxides, and a few less common compounds [26] and then must undergo metallothermic reduction to return to their March 28, 2011 [38], hybrid car s NiMH batteries contain between $165 and $250 of rare earth per battery [24]. A lanthanum based rare earth metal alloy is used as the active material of the negative electrode and the intermetallic contains cerium, praseodymium, and neodymium. It was metal state. The most common RE reduction method is calciothermic reduction which uses calcium as a reducing agent at high temperatures [37]. In order to extract REs, current best mining practices use a mix of primarily solvent extraction and ion exchange, with more specific methods sometimes integrating solid phase extraction, supercritical extraction, electro slag refining, electrowinning, and electrorefining processes. These processes fall into three main categories: hydrometallurgy which is variations of aqueous chemistry, electrometallurgy which is variations of electrolysis, and pyrometallurgy which is variations of thermal treatments. A variety of extraction methods can be seen in Table III. Urban mining would apply these processes in order to extract rare earths from waste instead of extracting rare earths from ores. C. Specific Products Urban Mining Potential Studies have successfully extracted rare earth elements from waste products in a lab setting but most of these methods have not been transferred over to the industrial sector. RE magnets are the main exception. Small quantities of magnet scrap are already recycled [2]. In 2010, the United Sates alone imported an estimated $113 million in refined rare earth metals [2]. This is in addition to all the rare earths the United Sates imports indirectly through end products like computers. Using rare earth prices from predicted that during 2010 the world would consume 27,300 tons of REs metals just for NiMH battery applications. Researchers have found methods to extract rare earth s from metal alloys, like those in NiMH batteries, with over 97% laboratory recovery rates by: grinding, leaching, and crystallization [34]; solvent extraction and stripping [39]; and leaching, liquid-liquid extraction, and stripping [40]. Catalytic converters and lighting phosphors are two other candidates for urban mining because of their high concentration of rare earths and pre-established collection infrastructure. Unfortunately many products have too low of a rare earth content to be candidates for urban mining. LCD screens are only 0.07 wt% rare earth which is lower than mine RE cut off grades [2]. NdFeB magnets are also low at only wt% Nd [23] but are already recycled because of the ease of recycling magnetic scrap back into the production streams. For RE products that can be mechanically separated or easily chemically separated, direct reuse of the products in the same supply chain could be an economical option even with low RE content. V. PHOSPHOR CASE STUDY Within a fluorescent lamp, phosphors convert the lamp s ultraviolet radiation into visible light. There are two types of fluorescent lamp phosphors, both of which contain rare earths,

4 halophosphate and the more efficient and rare earth heavy triphosphate. In 2009 the EPA passed higher efficiency requirements for fluorescent lamps and as a result NEMA predicted the demand from phosphors for REs to increase by 230% [24]. General purpose fluorescent lamp (GPFL) phosphors are a prime candidate for recycling. The lamps can be collected in large quantities since they are primarily used by businesses. Additionally, since fluorescent lamps contain mercury, recycling infrastructure already exists. A. Phosphor Composition The rest of this paper will focus on tri-phosphors because the majority of GPFLs disposed in the future will contain triphosphors in order to meet the EPA efficiency standards. Triphosphors are a mix of three phosphors: 55% red phosphor, 35% green phosphor, and 10% blue phosphor [41]. Typical fluorescent lamp phosphor compositions are Y 2 O 3 :Eu for red, LaPO 4 :Ce, Tb for Green, and BaMgAl 10 O 17 :Eu for blue [41]. The exact tri-phosphor composition varies company to company and thus this paper will focus on TCP s T5 linear fluorescent lamp. The T5, T8, T12 designation determines the radius of the bulb, 5/8, 8/8, and 12/8 respectively. Since the specification sheet defines the lamp content by weight percents, and phosphor composition already varies company to company, it is assumed that the T5 weight percent is representative of all bulbs considered. The T5 s weight percent relative to the entire bulb is wt% for Yt, wt% for Ce, wt% for Eu, wt % for Tb, and wt% for the entire phosphor [42]. For all analysis in the phosphor case study, the most conservative weight percent is used. B. Phosphor Manufacturing and Refurbishing Once the REs are in the separated oxide state, the general process for manufacturing phosphors starts with the refinement of raw materials: matrix, which contains the REs, activator, and flux. Next the raw materials undergo blending with a ball mill and blender, synthesis through firing, coarse crushing with a crusher and ball mill, classification through sedimentation, elutriation, and sieving, finishing through washing and surface treatments, and finally sieving [43]. The red phosphor, Y 2 O 3 :Eu, can be prepared by mixing the two oxides and firing at 1350C for 12 hours with flux [44]. The green phosphor, LaPO 4 :Ce, Tb is fired at 1200C for three hours in a reduced atmosphere [44]. The blue phosphor requires two firings with milling in between. The blue phosphor is fired at C, depending on the flux, in a reduced atmosphere [44]. C. Quantity of REs in Atlanta from Tri-phosphors In order to calculate the quantity of tri-phosphors in Atlanta it is assumed all commercial and industrial building use fluorescent lamps for their lighting needs. Even though this will result in a non-conservative estimate for commercial and industrial buildings, for the entire Atlanta metropolitan area the assumption will be balanced by the calculations not considering fluorescent lamps in residences and outdoors. During a fluorescent tube lifecycle study the DOE used two different T12 lamps with a mean light output of 2,880 lm and 2,300 lm, and T8 lamps with a mean light output of 2,520 lm as their baseline models for commercial and industrial properties. They determined the T8 market share to be 57%, the 2,520 lm T12 lamp s market share to be about 29% and the 3200 lm T12 lamp s market share to be about 14%. This results in an average light output of about 2814 lm for bulbs used in commercial and industrial buildings [41]. Table IV shows the calculation of the total lumens required to light different categories of commercial and industrial facilities. The Atlanta square footage data was obtained from the Sustainable Industrial Systems for Urban Regions (SISFUR) group at Georgia Tech. A conservative assumption was made that all of the light coming from the ceiling reaches the level of use, for which the lux requirements were designed. This results in Atlanta requiring almost 30.4 billion lumens which would be provided by approximately 10.8 million GPFLs. T8 and T12 bulbs are approximately 4 feet long. An Egyptian phosphor recycling study determined the average weight of bulbs approximately 4 feet long to be 129g [45]. Since bulbs vary manufacturer to manufacturer, the 129g was accepted as a reasonable weight within the standard weight range to use for analysis during this study. Considering these parameters and the fluorescent lamp weight percents, there is about 18,660 kg of Y, 6,220 kg of Ce, 18,660 kg of Eu, and 32,400 kg of Tb in fluorescent lamps in Atlanta. Based off March 2, 2011 prices [38], there is almost $46 million of REs in Atlanta, stored in fluorescent lamps. If bulbs are replaced every five years then every year in Atlanta over $9 million of REs leave the local economy when the bulbs are replaced. Ideally instead of extracting the REs, the supply chain could approach a closed loop system by refurbishing phosphors for direct reuse in fluorescent lamps. As of March 7, HEFA Rare Earth Products quoted their red phosphor Y 2 O 3 :Eu as $3.80/g, green phosphor (La,Ce,Tb)PO 4 :Ce,Tb as $4.00/g, and blue phosphor BaMgAl 10 O 17 :Eu as $3.80. Thus combining the phosphors into a tri-phosphor will cost at least $3.87/g. This is a conservative tri-phosphor cost estimate since there are processing costs from creating the tri-phosphor from the original phosphors. Considering this conservative triphosphor cost estimate and assuming an 85% process efficiency rate, the Atlanta metropolitan area could generate over $37 million annually in revenue from phosphor refurbishing just the fluorescent lamps from its locality. D. Current Recycling Infrastructure According to Ms. Linda Dunwoody of Veolia, a fluorescent bulb recycler, about 30% of fluorescent lamps are recycled.

5 Depending on the recycling company, businesses have the option to mail their fluorescent tubes in specially designed boxes, drop off their waste bulbs at regional disposal centers, or arrange pick up from a local recycling providers. EasyPak Recycling, a recycler based out of Illinois, charges $65.95 to recycle 32 T12 lamps or 64 T8 lamps. This price includes shipping, tracking, reports and certificates [46]. If phosphor refurbishment is incorporated into the fluorescent lamp recycling process, then recyclers could potentially start buying fluorescent lamps from corporations instead of charging a fee. This would presumably result in an almost 100% recycling rate. Recyclers currently use either a crushing then separation method or a separation the crushing method. For the crushing method, the fluorescent lamp is crushed then sent through a series of colanders which separate the glass and aluminum. A triple distiller extracts mercury from the remaining powder then the powder is land-filled. The land-filled powder consists of the lamp s phosphor and components of the lamp s cathode, such as tungsten wire, that were not removed during the aluminum and glass separation steps. The second method cuts off the aluminum end caps and blows the powder out of the glass tube before crushing the class. This method prevents the cathode elements from intermixing with the final powder product. The phosphor is then sent to a triple distiller that extracts the mercury. Both methods landfill the extracted powder which contains valuable RE elements. E. Recycling Phosphors If phosphor recycling occurs, the environmental effects from the flux agents and firing during phosphor manufacturing and the earlier discussed environmental effects from mining can be avoided. The powders from fluorescent lamps will still need to be processed before being reused in new fluorescent lamps. During lamp manufacturing, the phosphors are part of a phosphor suspension which typically includes a binder and solvents for the binder and may also include surfactants, defoamers, and submicron particle size alumina [49]. These elements will either need to be removed from the lamp powder mix or refurbished with the phosphors with the goal of refurbishing to the phosphor suspension state instead of the phosphor state. Researchers have successfully extracted REs and recovered phosphor products in a laboratory setting. Several studies can be seen in Table V. It is critical to note that an economical, industrial scale lamp powder to production phosphor process has not been developed as of the writing of this paper. Even though an economical, industrial scale phosphor recycling process does not exist, there is great interest within industry. Rhodia, a phosphor producer, has successfully developed a phosphor refurbishing process but the process has not been developed to an economical state [50]. In February 2011, Ms. Linda Dunwoody reported Veolia was attempting to develop a phosphor recycling process to incorporate into their recycling infrastructure. VI. CONCLUSION The RE supply and demand gap that developed after China decreased their RE exports opens a market for RE recycling. RE extraction from waste products has been successful in a laboratory environment but still needs to be developed to an economical state on an industrial scale. The most promising waste products are ones with already established collection or recycling infrastructure and products that contain high levels of REs. Unfortunately many RE applications contain too low of RE concentration to be considered for urban mining. RE urban mining should be pursued for its economic and environmental potential and its ability to supplement the RE supply. VII. ACKNOWLEDGEMENT The authors would like to thank the other members of the SISFUR group for their insight during the research process and data on the Atlanta metropolitan region. The authors would specifically like to thank Dr. Matthew Realff from the SISFUR group for reviewing the paper s RE extraction methods. VIII. REFERENCES [1] J. Kennedy, et al., "Critical and Strategic Failure of Rare Earth Resources," in 2010 SME Annual Meeting, Denver, CO, [2] USGS, "Rare Earths," United States Geological Association2010. [3] D. Kingsnorth. (2009). The Rare Earth Market: Can Supply Meet Demand in 2014? Available: AC09.pdf [4] Bloomberg News. (2010), China Cuts Export Quotas for Rare Earths by 35%. Bloomberg. Available: [5] Greenland Minerals and Energy Limited. Rare Earths at the crossroads. Industrial Minerals magazine, 8. Available: pdf [6] M. Lee, "China assures Clinton on rare earth exports," in Washington Post, ed. 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