Policy Analysis pubs.acs.org/est
Value Analysis of Neodymium Content in Shredder Feed: Toward Enabling the Feasibility of Rare Earth Magnet Recycling H. M. Dhammika Bandara, Julia W. Darcy, Diran Apelian, and Marion H. Emmert* Center for Resource Recovery and Recycling, Department of Chemistry and Biochemistry & Department of Mechanical Engineering, 100 Institute Road, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States S Supporting Information *
ABSTRACT: In order to facilitate the development of recycling technologies for rare earth magnets from postconsumer products, we present herein an analysis of the neodymium (Nd) content in shredder scrap. This waste stream has been chosen on the basis of current business practices for the recycling of steel, aluminum, and copper from cars and household appliances, which contain significant amounts of rare earth magnets. Using approximations based on literature data, we have calculated the average Nd content in the ferrous shredder product stream to be between 0.13 and 0.29 kg per ton of ferrous scrap. A value analysis considering rare earth metal prices between 2002 and 2013 provides values between $1.32 and $145 per ton of ferrous scrap for this material, if recoverable as pure Nd metal. Furthermore, we present an analysis of the content and value of other rare earths (Pr, Dy, Tb).
1. INTRODUCTION The recent implementation of export restrictions on rare earth (RE) elements and RE containing products by China has resulted in price explosions for these materials in 2011. Manufacturers of hybrid and electric cars, electric motors, actuators, turbines, and hard disk drives in the U.S. and elsewhere have been struggling to cope with unstable prices, as many of these technologies require the RE elements neodymium (Nd), dysprosium (Dy), or samarium (Sm) as raw materials for strong and light magnets.1−3 This issue provides a strong motivation for the United States to invest in methods for price stabilization of REs as critical materials.4 Typical approaches to this end include stockpiling, substitution, and recycling.5,6 However, despite recent efforts, none of these strategies are currently implemented on a large scale.7 Recycling can lessen the impact of external factors on the price and thus aid in stabilizing market prices.8,9 With respect to RE magnets, technologies for the recovery, reuse, and recycling of magnetic scrap and chips generated as waste during manufacturing have already been developed.10 However, no existing commercial process in the U.S. recycles RE magnets from end-of-life products such as used cars and household appliances. Reasons for this, among others, are the lack of data on the quantity of RE materials from magnets in waste streams and on the fate of magnets after shredding.11 Herein, we focus on quantifying the amount of Nd in current (2013) shredder product streams, as NdFeB magnets are the most widely used types of RE magnets and critical materials for the further implementation of sustainable technologies such as wind turbines and electric vehicles. Based on the obtained data, © 2014 American Chemical Society
we further estimate the value of Nd and other REs from magnets that can be recovered through recycling end-of-life cars and household appliances. Since SmCo magnets are typically not used in motors unless durability at high temperatures is required,12 the analysis herein focuses only on NdFeB magnets. Furthermore, SmCo magnets have a much smaller market share than NdFeB magnets, and are thus not expected in substantial amounts in the shredder product stream.13
2. MATERIALS AND METHODS 2.1. Approach. In order to quantify the amount of Nd contained in shredder input and product streams, three variables need to be known: (i) the composition of shredder feed, (ii) the weight percentage of ferrous materials in each source of shredder feed, and (iii) the average weight of Nd in each source. These three variables are treated separately below in order to estimate the Nd content of the shredder feed and the ferrous shredder product stream. Overall, we assume that magnetic materials including RE magnets will be located together with steel in the ferrous output of shredders, as the separation of ferrous materials from nonferrous materials is achieved through a magnetic separation step.14 The part of ferrous scrap found in shredder residue has been considered separately (see SI). Received: Revised: Accepted: Published: 6553
November 18, 2013 April 3, 2014 May 21, 2014 May 21, 2014 dx.doi.org/10.1021/es405104k | Environ. Sci. Technol. 2014, 48, 6553−6560
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Figure 1. Lifecycle of Nd magnets between end-of-life product and shredder scrap separation.14,19
Figure 2. (A) Total weight and calculated ferrous materials content (68%) in LDVs. (B) Calculated age distribution of LDVs shredded in 2013. (C) Estimated average weight of Nd mNd,i in a LDV vs year of manufacturing. (D) Calculated weight of Nd in ferrous materials xi from LDVs vs manufacturing year. Vertical axis shows Nd content in g per kg of ferrous scrap.
2.2. Shredder Feed Composition. Typical shredder feed materials include light duty vehicles (LDVs), discarded household appliances, and other sources of steel scrap, such as dismantled bridges, steel from demolished buildings, and discarded railroad cars (Figure 1).14,15 The LDV category consists of passenger cars, passenger vans, sports utility vehicles (SUVs), and light trucks. 16 The category “household appliances” includes only major appliances (refrigerators, washing machines, air conditioners).17,18 The exact composition of shredder feed determines the ratio and the quality of the product streams (e.g., ferrous vs nonferrous scrap) and is thus a closely guarded trade secret of shredder operators. However, average values for shredder feed compositions can be found to be 15−50% household appliances, 40−80% cars, and 10−15% other sources by weight, with the variations reflecting regional availabilities, seasonal variations, and existing materials contracts.14,19 Using these literature data for the ratio of end-of-life products in the feed and information about the ferrous materials content in
each source, we can determine the weight percentage of ferrous materials in the shredder feed (see 2.3). This is crucial, as RE magnets are expected to be located in the ferrous product stream due to their intrinsic magnetic properties. 2.3. Weight Percentage of Ferrous Materials in Scrap Sources. After shredding, ferrous and nonferrous scrap is separated using a drum magnet (Figure 1).14 The nonferrous fraction is further sorted to separate nonferrous metals (zinc, copper, aluminum, brass, and some stainless steel) from nonmetallic materials (plastics, glass, foam and fabrics). The ferrous product is typically the main product of a shredder operation and is sold to steel mills to produce recycled steel.14 The relative amounts of ferrous and nonferrous materials in the overall product streams can be determined by considering the average ferrous content in each source of shredder feed (LDVs, household appliances, and other sources). 2.3.1. Ferrous Content of LDVs. The weight percentage of ferrous materials in LDVs has remained between 65 and 70% since the early 1970s,19−24 despite a significant increase in 6554
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vehicle weight since then (Figure 2A).23 For the calculations herein, we approximate that the average value of 68 weight-% is a good representation of the ferrous materials content of LDVs.24 2.3.2. Ferrous Content of Household Appliances. Major household appliances contain between 25% and 51% of ferrous materials by weight. For the following calculations, we assumed that household appliances contain 40% ferrous materials by weight, which is the calculated average of several reported ferrous materials contents.25−27 2.3.3. Ferrous Content of Other Sources of Scrap. Other sources of scrap include steel beams from dismantled bridges, steel from demolished buildings and railroad cars. These sources consist of almost 100% of ferrous materials;15 thus, we approximate their ferrous materials content to be 100% for further calculations. Based on the approximations above and on the data for the composition of shredder feed, we calculate that the ferrous scrap stream is by far the largest shredder product stream by weight (57−69%; literature values are 60−80%).14,19 2.4. Neodymium Content in Different Scrap Sources. To the best of our knowledge, the Nd content in U.S. shredder scrap has not been determined. Therefore, we use estimates to determine the amount of Nd in the three main components of shredder feed (LDVs, household appliances, and other sources), which are then used to calculate the Nd content in ferrous scrap. 2.4.1. Other Sources of Scrap. As mentioned before, other sources of scrap mainly consist of construction materials and railroad cars.14 We do not expect RE magnets in any of these sources as they typically do not contain electric motors or other magnetic materials. Hence, we assume a Nd content of 0% for other sources of scrap. 2.4.2. Household Appliances. Nd contents of some common household appliances sold in the U.S. have been reported.28,29 However, these data in combination with annual sales data and average lifetimes1,18 are not sufficient to accurately estimate the amount of Nd from all shredded appliances. More accurate data are available for shredded waste electronic and electric equipment (WEEE) in the U.K., for which the Nd content has been experimentally determined to be 0.70 g Nd per 1 kg of ferrous shredder scrap.30 WEEE mainly consist of mixed household appliances (69% by weight) such as refrigerators (containing 40−60 g NdFeB magnets per unit), washing machines (80−180 g NdFeB/unit), and air conditioners (60−400 g NdFeB/unit).29,31 When adjusting the average value for the Nd content (0.70 g Nd/kg ferrous scrap) for contributions from electronics8,32 and other materials present (e.g., lighting equipment; for the calculations see the SI), a value of 0.61 g Nd per kg ferrous scrap can be derived for major household appliances. The original value (0.70 g Nd/kg ferrous scrap) as well as the adjusted value (0.61 g Nd/kg ferrous scrap) will both be used in final calculations of the Nd content in ferrous scrap. We postulate that the data derived from U.K. WEEE are a good approximation for the Nd content in household appliances shredded in the U.S. This hypothesis is based on several similarities between the U.S. and the U.K. recycling enterprise. First and foremost, the collection of household appliances is nonmandatory in both countries, unlike in most other European nations.29,30 Second, both nations are among the most developed countries in the world, which can be documented by different metrics such as the 2012 gross
national income per capita ($43,480 for the U.S.; $32,538 for the U.K.),33 the 2012 human development index (0.94 out of 1 for the U.S.; 0.88 for the U.K.),33 and the 2011 gross average monthly wage ($4538 for the U.S.; $4199 for the U.K.).34 Third, according to data released by the U.S. Association of Home Appliance Manufacturers and the City of York recycling facility (U.K.), household appliances to be recycled in both countries are of very similar average weight (58−63 kg/unit for the U.S.; 56 kg/unit for the U.K.).35−37 Based on these data, we postulate that the value of 0.70 g/kg ferrous scrap derived from studies in the U.K. as well as the calculated value of 0.61 g Nd/ kg ferrous scrap are good assumptions for the Nd content of ferrous scrap from U.S. household appliances. Both values will be used below to calculate the total Nd content in the ferrous scrap stream in dependence on the shredder feed composition. 2.4.3. LDVsGeneral Approach. Arriving at a good approximation for the Nd content in shredded LDVs is challenging because currently shredded LDVs have been manufactured over a broad range of years. During this time, the weight of LDVs and their ferrous materials content has changed significantly as discussed before (see Figure 2A). Additionally, changes in the Nd content of the vehicles during this period have occurred because NdFeB magnets have only been introduced to the market in 1984.38 Thus, an increase in the amount of Nd in vehicles manufactured in the last decades seems likely, as the electrification of vehicles and, with it, the use of magnets in speakers and various types of motors has steadily progressed.39 Therefore, the age distribution of LDVs, the weight of Nd in shredded LDVs, and the weight of ferrous materials all need to be calculated to approximate the Nd content in currently shredded LDVs. The age distribution of LDVs can be expressed as a series of values wi, which stand for the percentage-wise contribution of vehicles manufactured in year i to the overall population of currently shredded LDVs. Additionally, values xi for the amount of Nd in ferrous scrap from shredding LDVs manufactured in year i need to be known. With these variables, the average Nd content in ferrous scrap x̅ can be calculated using the average mean method (eq 1). The values of xi can be determined using eq 2 and the variables mNd,i (the average weight of Nd in an LDV produced in year i) and mferrous,i (the weight of ferrous materials in an LDV produced in year i).
x̅ = xi =
∑ wx i i ∑ wi
(1)
mNd, i mferrous, i
(2)
2.4.3.1. Age Distribution of Shredded LDVsDetermining wi. No data is available on the age distribution of LDVs shredded at present in the U.S. However, the age distribution of LDVs shredded in 1995 in the U.S. has been reported.40 This distribution is best described by a Weibull distribution function (eq 3), in which wi is the percentage of LDVs manufactured in a previous year i that makes up the population of LDVs being shredded at present. ⎛ i−i ⎞ −⎜ 0 ⎟ α wi = 100 × α (i − i0)α − 1e ⎝ β ⎠ β
α
(3)
This function and with it the parameters wi are determined by the manufacturing year i, the oldest manufacturing year in the distribution i0, and the mean lifetime of LDVs. In 6555
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vehicles manufactured between 1985 and 2012, using an approximation of 68% for all our calculations as discussed in section 2.3.1 (see also Figure 1). 2.5. Nd Content in Ferrous ScrapDetermining xi and x.̅ By substituting the values for the weight of ferrous materials mferrous,i and the total weight of Nd in an LDV mNd,i in eq 1, the weight percentage xi of Nd in ferrous scrap from LDVs manufactured in year i can be calculated (see Figure 2D). For example, a typical LDV built in 2000 weighs 1732 kg. Ferrous materials account for 68% of this weight and thus mferrous,2000 equals 1178 kg (68% × 1732 kg). The weight of Nd mNd,2000 in the LDV is 134 g; therefore, the Nd content in ferrous scrap x2000 which is produced by shredding this average LDV is 0.11 g/kg (134 g/1178 kg). By entering all the obtained values for xi and wi into eq 2, the Nd content in the part of ferrous scrap that is generated through shredding LDVs was calculated to be on average 0.10 g per kg ferrous scrap (for detailed calculation and tabulation of xi and wi see the SI).
agreement with the literature, we assume for our calculations that the oldest shredded vehicles in the LDV population are 28 years old and that the mean lifetime is 13 years.20,41 With these assumptions, the parameters α and β are two empirical constants that have been determined to fit the Weibull distribution to the observed data; literature precedent suggests values of α = 7.3 and β = 14.8 to be a good fit, which will be used for further calculations.41 Adapting the Weibull distribution function to estimate the age distribution of LDVs shredded in 2013 then leads to an age distribution as shown in Figure 2B. Interestingly, a large majority (nearly 75%) of LDVs that are shredded at present have been manufactured in the short time span between 1997 and 2001. Therefore, we expect that the amount of Nd in cars built during these 5 years will be crucial for the Nd content in scrap generated in 2013 from shredding LDVs. More recent data on the age distribution of shredded cars in Connecticut from 2007 confirm that the Weibull distribution discussed above is still valid for approximating the age distribution of today’s shredded LDVs.40 The mean age of cars determined by this more recent publication is 16 years, which is very similar to the function used above (13 years). At the same time, the oldest shredded cars in 2007 were shown to be 30 years old, which is very close to the age of the oldest cars assumed above (28 years). Since both distributions show slightly different values, the Nd content in the ferrous shredder stream has been calculated for both distributions (see below and SI). The effect of using different age distributions on the Nd content and the value analysis will be discussed in the Results and Discussion section. 2.4.3.2. Total Weight of Nd in LDVs − Determining mNd,i. In order to determine mNd,i (the Nd content of a vehicle produced in year i) we use the only available literature data on the Nd content of average LDVs manufactured in the years 2012 and 1995. Kirchain and co-workers have determined the total amount of Nd in the 11 most common motors of a typical 2012 model year sedan to be 173 g per car, which allows us to estimate the average amount of Nd to be 16.3 g per motor (173 g/11).42 Fastenau and Loenen report that LDVs manufactured in 1995 contain on average 60 motors and that 7% of these motors contain NdFeB magnets.43 Using the same value as above for the average weight of Nd in a motor (16.3 g), the total amount of Nd in a typical LDV manufactured in 1995 was calculated to be 68.5 g (7% × 60 motors × 16.3 g). Next, we assume that the total amount of Nd in an LDV increased linearly over the years with the stepwise incorporation of NdFeB magnet technology. This approach provides the total weight of Nd in a car in dependence on its year of manufacturing (Figure 2C). According to our estimates, no Nd from NdFeB magnets should be present in cars built prior to 1989. This is, in our opinion, supported by data for the market share of NdFeB magnets in 1988, which is 0.14% of the total number of magnets produced globally.44 Because these magnets were discovered only in 1984,38 both their low market share and the lack of their incorporation in LDVs seem reasonable. 2.4.3.3. Weight of Ferrous Materials in LDVs − Determining mferrous,i. The average weight of LDVs in the U.S. has increased from 1483 to 1841 kg between 1985 and 2005, and remained relatively constant since 2005. However, the weight percentage of ferrous materials in LDVs has remained between 66 and 70% of the total weight since 1985.22 This allows us to calculate the weight of ferrous materials in
3. RESULTS AND DISCUSSION 3.1. Quantifying Nd in Ferrous Scrap. Our estimates of the Nd and ferrous materials content in each scrap source and the literature-known ranges of shredder feed composition (40− 80% LDVs, 15−50% household appliances, and 10−15% other sources)14,19 allows us to quantify the amount of Nd in ferrous shredder scrap produced in 2013. Household appliances contain the largest amount of Nd per weight of ferrous scrap (0.70 g per kg of ferrous scrap); in comparison, the Nd content in shredded LDVs is much lower (0.10 g per kg of ferrous scrap) and other sources (railroad cars, dismantled bridges etc.) do not contain any Nd. Therefore, we expect that a shredder feed with the largest amount of household appliances and the smallest amount of other sources contains the maximum amount of Nd. Consequently, the minimum amount of Nd is present in a shredder feed with a minimum amount of household appliances and a maximum amount of other sources. Both of these cases are discussed below in detail. Maximum Nd Content. The weight percentage of household appliances in shredder feed does not exceed 50% and, at the same time, the minimum weight percentage of other sources cannot be less than 10%.14 Therefore, a shredder feed consisting of 50% household appliances, 40% cars, and 10% other sources will produce ferrous scrap with a maximum Nd content. Based on our calculations, the total amount of Nd can thus be estimated to be 167 g/572 kg = 0.29 g/kg ferrous scrap under these conditions (see Table 1). Minimum Nd Content. In analogy, the Nd content in ferrous scrap will be minimized using a shredder feed Table 1. Maximum Nd Content in Ferrous Scrapa
scrap source household appliances LDVs other sources total a
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% of total scrap feed
% ferrous in source
ferrous scrap per 1000 kg shredder feed
Nd content per kg ferrous scrap by source
weight of Nd in 1000 kg shredder feed by source
50%
40%
200 kg
0.70 g
140 g
40% 10%
68% 100%
272 kg 100 kg
0.10 g 0g
27 g 0g
572 kg
167 g
All percentage values are weight-%. dx.doi.org/10.1021/es405104k | Environ. Sci. Technol. 2014, 48, 6553−6560
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parts, no processes are operational yet. However, due to the considerable Nd content in hybrid vehicles, we expect that the Nd content of shredder feeds in the future can be influenced significantly when a high market penetration is achieved. 3.3. Value of REEs in Ferrous Scrap. Importantly, with our calculations of the minimum and maximum content of Nd in ferrous shredder scrap, we are now able to determine the respective value of the recoverable REs. This is crucial, as the establishment and continuous use of practical recycling technologies for RE magnets is dependent on their commercial feasibility. Additional separation, isolation and purification steps will be required to recover pure Nd from ferrous scrap. Thus, the materials values calculated herein can only be one of the factors that need to be considered for establishing new recycling technologies. Value of Nd. For the following value calculations, Nd prices were based on the market prices for pure Nd from the German Institute for Rare Earths and Metals.48 In order to gain a better insight into the possible price ranges, we have considered (i) the maximum price of Nd ever observed (August 2011; $500/ kg), (ii) the minimum price of Nd from the 10 year period before the price spike (August 2002; $12.00/kg), and (iii) current pricing from August 2013 ($95/kg; Table 3).49 Furthermore, we have tabulated both the maximum (0.29 g per kg) and minimum (0.13 g per kg) Nd content in ferrous scrap, which is dependent on the composition of shredder feed, as discussed above. Using this approach, we estimate that 1 t of ferrous scrap contains Nd with a value between $1.56 and $145. In analogy, the value of Nd in the ferrous product stream of smaller shredders processing 2000−3000 t per month50 (∼75% ferrous scrap14) can be estimated to be between $2340 and $326,250 (Table 3). With modified (see SI) values (age distribution of shredded LDVs from 2007; adjusted Nd content of major household appliances), price ranges of $1.32 to $140 per ton of ferrous scrap ($1980 to $315,000 per monthly output of smaller shredder) are obtained in analogous calculations, which are in the same order of magnitude as the above discussed values. Value of Other RE Elements. Due to the similar chemical reactivities of the rare earth elements, a recovery process for Nd from magnets would most likely also recover any other rare earth metals present in magnets. For example, NdFeB magnets can contain up to 9% of other RE elements such as dysprosium (Dy), terbium (Tb), and praseodymium (Pr) in addition to Nd.6 Our calculations above enable us to estimate the maximum amounts of these elements that might be present in the recovered mixture of rare earth elements and to estimate a maximum value for the present amounts. Prices for Pr are typically lower than for Nd, and manufacturers have added Pr to RE magnets during times of high prices for Nd in order to lower production costs.8 Since Pr is added in very small quantities (≤5% of the weight of Nd) the
composition with the lowest possible weight percentage of household appliances and the highest possible weight percentage of other scrap sources. This estimation results in a shredder feed composition of 15% household appliances, 15% other sources, and thus 70% LDVs, providing a minimum Nd content of 90 g/686 kg = 0.13 g/kg ferrous scrap (see Table 2). Table 2. Minimum Nd Content in Ferrous Scrapa
scrap source household appliances LDVs other sources total a
% of total scrap feed
% ferrous in source
ferrous scrap per 1000 kg shredder feed
Nd content per kg ferrous scrap by source
weight of Nd in 1000 kg shredder feed by source
15%
40%
60 kg
0.70 g
42 g
70% 15%
68% 100%
476 kg 150 kg
0.10 g 0g
48 g 0g
686 kg
90 g
All percentage values are weight-%.
Analogous calculations have been performed (see SI) using (i) an age distribution of shredded cars from 2007;40 (ii) an adjusted value for the Nd content of household appliances; and (iii) using both of these modifications in our Nd content calculations. The results are close to the above-discussed outcomes and provide ranges of 0.11 to 0.28 g Nd per kg ferrous scrap. Due to these very close results we will use the original values of 0.13 to 0.29 g Nd per kg ferrous scrap to discuss exemplary price calculations further below. Analogous price calculations for the modified Nd content values are provided in the SI. 3.2. Influence of Hybrid and Electric Vehicle Use on Nd Content. One factor that could substantially influence the Nd content in shredded LDVs is the presence of electric and hybrid vehicles in the shredder feed. According to Kirchain, a typical hybrid car with a NiMH battery contains approximately 3.2 kg of Nd. 2.4 kg of Nd are located in the battery which is removed prior to shredding, but the remaining amount of Nd (0.80 kg) is still significantly higher than the Nd content in a typical conventional car (0.29 kg).34 Most cars that constitute the LDVs in shredder feed in 2013 were manufactured between 1998 and 2001 (see Figure 2B above). In 2000, hybrid and electric vehicles accounted for only 0.10% of car sales in the U.S., which we assume to be a good estimate of sales for the years between 1998 and 2003.45,46 Due to this very low number, we conclude that the presence of hybrid and electric vehicles has a negligible influence on the Nd content in ferrous scrap for today’s shredder operations, especially since most of these vehicles are currently not sent to shredders as only one process for the recovery of REs from NiMH batteries has been established.47 For other precious
Table 3. Minimum and Maximum Values of Nd Content in Ferrous Scrap Nd market price49 $12/kg Nd (August 2002) $500/kg Nd (August 2011) $95/kg Nd (August 2013)
Nd content per kg ferrous scrap 0.13 0.29 0.13 0.29 0.13 0.29
g g g g g g
value of Nd per ton ferrous scrap
value of Nd in ferrous scrap output (1500−2250 t) of smaller shredder per month50
$1.56 $3.48 $65.00 $145.00 $12.35 $27.55
$2340 to $3510 $5220 to $7830 $97,500 to $146,250 $217,500 to $326,250 $18,525 to $27,788 $41,325 to $61,988
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Environmental Science & Technology value of Pr in ferrous scrap is estimated to be much lower than that of Nd ($3.75 per ton of ferrous scrap; Table 4).
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Table 4. Value of Rare Earth Elements other than Nd in Ferrous Scrap
The Supporting Information includes detailed calculations of the Nd content in LDVs. This material in available free of charge via the Internet at http://pubs.acs.org.
rare earth element
maximum price per kg in 201149
maximum weight per ton of ferrous scrapa
maximum value of rare earth elements per ton of ferrous scrap
Pr Dy Tb
$250 $3100 $5000
0.015 kg 0.015 kg 0.015 kg
$3.75 $46.50 $75.00
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ASSOCIATED CONTENT
S Supporting Information *
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AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected]. Notes
The authors declare no competing financial interest.
a
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Based on the maximum weight of Nd per ton of ferrous scrap 0.29 kg × 5 weight-% = 0.015 kg.
ACKNOWLEDGMENTS This work was supported by WPI, NSF (IIP-0968839) and the members of the I/U CRC Center for Resource Recovery and Recycling (CR3). We thank all members of CR3 for valuable discussions. In particular, we acknowledge Jeff Webster (previously wTe, now Victaulic Corp.), Mark Bauer (GM), Yan Wang (WPI), and Jerry Schaufeld (WPI) for their valuable input.
Dy and Tb are added to NdFeB magnets to increase the operating temperature window of the magnets. Both elements are significantly more expensive than Nd, and are thus preferentially added in very small quantities. As such, the Dy content found in magnets for motors is typically not higher than 5%.6,8 If all NdFeB magnets are assumed to contain 5% of Dy, the maximum value of recoverable Dy per ton of ferrous scrap is $46.50, based on the highest historic Dy prices in 2011. In analogy, if 5% Tb is used in all magnets instead of Dy, the maximum value of recoverable Tb is $75.00. However, not all NdFeB magnets contain 5% of Dy or Tb. Therefore, the actual value of Dy and Tb in ferrous scrap is expected to be typically much lower than these estimated maximum values.
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ABBREVIATIONS B boron Co cobalt Dy dysprosium Fe iron HVAC heating, ventilation, and air conditioning LDV light duty vehicle Nd neodymium NiMH nickel metal hydride Pr praseodymium RE rare earth(s) REE rare earth element(s) Sm samarium Tb terbium WEEE waste electronic and electric equipment
4. SUMMARY AND CONCLUSIONS In summary, we have estimated the content of Nd in ferrous scrap shredded in 2013. Based on the lifecycle of end-of-life light-duty vehicles (LDVs) and household appliances, we have estimated a maximum and minimum Nd content in ferrous shredder scrap (0.13 and 0.29 g of Nd per kg of ferrous scrap). Furthermore, we have considered the influence of the presence of hybrid and electric vehicles in the relevant waste streams. Using historical and current market prices, we were able to estimate the value that could be generated by recovering Nd and other rare earth elements from the ferrous scrap product stream. The value of recoverable Nd varies greatly between $1.32 and $145 per ton of ferrous scrap, reflecting the large price fluctuations between 2002 and 2013. In contrast, the used age distribution of shredded cars and modifying the Nd content of major household appliances have only a minor effect on the value analysis. The model calculations used herein are flexible to accommodate changes in the waste streams that are expected for the future−for example, when hybrid and electric vehicles reach a higher market penetration. We expect that the results of our analysis will be one factor that helps to determine the feasibility of recycling and recovery technologies for rare earths from end-of life magnets. However, before recycling of end-oflife rare earth magnets will become a reality many challenges11 still need to be addressed: (i) Identification of the RE containing shredder product stream(s) (e.g., steel scrap or copper pickings);51 (ii) development of sortation technologies that accumulate RE containing materials in real time; (iii) selective leaching of RE contents; (iv) separation and recovery of REs. Creating such technologies in a sustainable and economically sound fashion is the focus of our future work in this area.
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REFERENCES
(1) Du, X.; Graedel, T. Global in-use stocks of the rare earth elements: A first estimate. Environ. Sci. Technol. 2011, 45 (9), 4096− 4101. (2) Dent, P. Rare earth elements and permanent magnets. J. Appl. Phys. 2012, 111, 1−6. (3) Gutfleisch, O.; Willard, M.; Bruck, E.; Chen, C.; Sankar, S.; Liu, J. Magnetic materials and devices for the 21st century: Stronger, lighter and more energy efficient. Adv. Mater. 2011, 23 (7), 821−842. (4) Jacoby, M.; Jiang, J. Securing the supply of rare earths. Chem. Eng. News 2010, 88 (35), 9−12. (5) Alonso, E.; Field, F.; Gregory, J.; Kirchain, R. Material availability and the supply chain: Risks, effects and responses. Environ. Sci. Technol. 2007, 41 (19), 6649−6656. (6) Binnemans, K.; Jones, P.; Blanpain, B.; Gerven, T.; Yang, Y.; Walton, A.; Buchert, M. Recycling of rare earths: A critical review. J. Clean. Prod. 2013, 51, 1−22. (7) Molycorp, Molycorp Mountain Pass, http://www.molycorp. com/about-us/our-facilities/molycorp-mountain-pass (accessed August 2013). (8) Rademaker, J.; Kleijn, R.; Yang, Y. Recycling as a strategy against rare earth element criticality: A systematical evaluation of the potential yield of NdFeB magnet recycling. Environ. Sci. Technol. 2013, 47 (18), 10129−10136. (9) Alonso, E.; Sherman, E.; Wallington, T.; Everson, M.; Field, F.; Roth, R.; Kirchain, R. Evaluating rare earth element availability: A case 6558
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with revolutionary demand from clean technologies. Environ. Sci. Technol. 2012, 46 (6), 3406−3414. (10) U. S. Department of Energy, Ames National Laboratory, Reclaiming Rare Earths. https://www.ameslab.gov/news/newsreleases/reclaiming-rare-earths (accessed August 2013). (11) Darcy, J. W.; Bandara, H. M. D.; Mishra, B.; Blanplain, B.; Apelian, D.; Emmert, M. H. Challenges in recycling end-of-life rare earth magnets. JOM 2013, 65 (11), 1381−1382. (12) (a) Constantinides, S. Rare Earth Materials. How Scarce Are They? Management Conference of the Motor and Motion Association, Spring 2010, Fort Myers, FL. http://www.arnoldmagnetics.com/ WorkArea/DownloadAsset.aspx?id=5323 (accessed March 2014). (b) Liu, J.-F.; Choi, H.; Walmer, M. Design of permanent magnet systems using finite element analysis. J. Iron Steel Res. Int. 2006, 13, 383−387. (13) Constantinides, S. The Demand for Rare Earth Materials in Permanent Magnets. 51st Annual Conference of Metallurgists (COM), October 2012, Niagara Fallas, Canada. http://www.arnoldmagnetics. com/WorkArea/DownloadAsset.aspx?id=5933 (accessed March 2014). (14) Brahmst, E. Copper in End-of-Life Vehicle Recycling. The Center for Automotive Research, Ann Arbor, MI, 2006. (15) Fenton, M. Iron and Steel Recycling in the United States in 1998, The U. S. Geological Survey, Open File-Report 01-224, 1998. (16) U. S. Environmental Protection Agency. Vehicle Weight Classifications. http://www.epa.gov/otaq/standards/weights.htm (accessed August 2013). (17) U. S. Environmental Protection Agency. Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2010. http://www.epa.gov/osw/nonhaz/municipal/pubs/msw_ 2010_factsheet.pdf (accessed March 2014). (18) U. S. Environmental Protection Agency. Responsible Appliance Disposal Program, Annual Report, 2011. (19) Kim, J.; Bae, J.; Allenby, B. Recycling Systems and Management of End-of-Life Vehicles (ELVs), Center for Sustainable Engineering, 2007. (20) Jody, B.; Daniels, E.; Duranceau, C.; Pomykala, J.; Spangenberger, J. End-of-Life Vehicle Recycling: State of the Art of Resource Recovery from Shredder Residue. U. S. Department of Energy, Argonne National Laboratory, 2010. (21) Duranceau, C.; Spangenberger, J. All Auto Shredding: Evaluation of Automotive Shredder Residue Generated by Shredding only Vehicles; U. S. Department of Energy, Argonne National Laboratory, 2011. (22) Das, S.; Curlee, R.; Rizy, C.; Schexnayder, S. Automobile recycling in the United States: Energy impacts and waste generation. Resour. Conserv. Recycling 1995, 14 (3-4), 265−284. (23) U. S. Environmental Protection Agency, Light Duty Automotive Technology, Carbon Dioxide Emissions and Fuel Economy Trends: 1975 Through 2012. http://www.epa.gov/fueleconomy/fetrends/19752012/420r13001.pdf (accessed August 2013). (24) Staudinger, J.; Keoleian, G. Management of End-of-Life Vehicles in the US, Report No. CSS01-01; Center for Sustainable Systems, University of Michigan, 2001. (25) Dillon, P. S. Salvageability becoming law. Spectrum, IEEE 1994, 31 (8), 18−21. (26) Truttmann, N.; Rechberger, H. Contribution to resource conservation by reuse of electrical and electronic household appliances. Resour. Conserv. Recycling 2006, 48 (3), 249−262. (27) Matsuto, T.; Jung, C. H.; Tanaka, N. Material and heavy metal balance in a recycling facility for home electrical appliances. Waste Manage. 2004, 24 (5), 425−436. (28) Liu, R.; Buchert, M.; Dittrich, S.; Manhart, A.; Merz, C.; Schuler, D. Applications of Rare Earths in Consumer Electronics and Challenges for Recycling; IEEE International Conference on Consumer Electronics: Berlin, 2011. (29) Seo, Y.; Morimoto, S. Comparison of dysprosium security strategies in Japan for 2010−2030. Resour. Policy 2014, 39, 15−20. (30) James, A. Determination of Platinum Group Elements (PGE) and Rare Earth Elements (REE) in Waste Materials by Microwave Digestion
and ICP-MS to Assess the Potential for Economic Recovery. M. Sc. Thesis, Cranfield University, United Kingdom, 2011. (31) Ongondo, F. O.; Williams, I. D.; Cherrett, T. J. How are WEEE doing? A global review of the management of electrical and electronic wastes. Waste Manage. 2011, 31 (4), 714−730. (32) (a) Buchert, M.; Manhart, A.; Bleher, D.; Pingel, D. Recycling Critical Raw Materials from Waste Electronic Equipment; Oeko-Institut e.V.: Darmstadt, 2012; http://www.oeko.de/oekodoc/1375/2012010-en.pdf (accessed March 2014). (b) Manhart, A.; Buchert, M.; Bleher, D.; Pingel, D. Recycling of Critical Metals from End-of-Life Electronics, Electronics Goes Green 2012+ (EGG), 2012, 9−12 Sept. 2012; pp 1−5. (c) Hurst, C., Japan’s Approach to China’s Control of Rare Earth Elements. China Brief 2011, 11 (7). http://fmso. leavenworth.army.mil/documents/Japan%27s-approach.pdf (accessed March 2014). (33) United Nations Development Programme, Table 1: Human Development Index and its components. https://data.undp.org/dataset/ Table-1-Human-Development-Index-and-its-components/wxub-qc5k (accessed March 2014). (34) U.N. Economic Commision for Europe, Gross Average Monthly Wages by Country and Year. http://w3.unece.org/pxweb/dialog/varval. asp?ma=60_MECCWagesY_r&path=../database/STAT/20-ME/3MELF/&lang=1&ti= Gross+Average+Monthly+Wages+by+Country+and+Year (accessed March 2014). (35) Sahni, S.; Boustani, A.; Gutowski, T.; Graves, S. Appliance Remanufacturing and Energy Savings, MIT Energy Initiative Report Series, MITEI-1-a-2010. http://web.mit.edu/ebm/www/Publications/ MITEI-1-a-2010.pdf (accessed March 2014). (36) American Iron and Steel Institute. The New Steel. Appliance Recycling for Environmentally Friendly Consumers. http://www.steel. org/The%20New%20Steel/∼/media/Files/AISI/Steel%20Markets/ fs_Appliance_sept2010.ashx (accessed March 2014). (37) City of York Council. Recycling and Re-use Scrutiny SubCommittee, Final Report − Recycling and Reuse − Removing Bulky Items from the Waste Stream, Annex C. http://democracy.york.gov.uk/ documents/s2116/ Annex%20C%20REcycling%20Report%20frnweights2005.pdf (accessed March 2014). (38) Sugimoto, S. Current Status and Recent Topics of Rare Earth Permanent Magnets. J. Phys. D: Appl. Phys. 2011, 44 (6), 064001. (39) Boulanger, A. G.; Chu, A. C.; Maxx, S.; Waltz, D. L. Vehicle Electrification: Status and Issues. Proc. IEEE 2011, 99 (6), 1116−1138. (40) Muller, D.; Cao, J.; Kongar, E.; Altonji, M.; Weiner, P.; Graedel, T. Service Lifetimes of Mineral End Users. U. S. Geological Survey Mineral Resources External Research Program Report, 2006. http:// minerals.usgs.gov/mrerp/reports/Mueller-06HQGR0174.pdf (accessed March 2014). (41) van Schaik, A.; Reuter, M. A.; Boin, U. M. J.; Dalmijn, W. L. Dynamic modelling and optimization of the resource cycle of passenger vehicles. Miner. Eng. 2002, 15 (11), 1001−1016. (42) Alonso, E.; Wallington, T.; Sherman, A.; Everson, M.; Field, F.; Roth, R.; Kirchain, R. An assessment of the rare earth element content of conventional and electric vehicles. SAE Int. J. Mater. Manf. 2012, 5 (2), 473−477. (43) Fastenau, R. H. J.; van Leonen, E. J. Applications of Rare Earth Permanent Magnets. J. Magn. Magn. Mater. 1996, 157, 1−6. (44) Smith, V.; Keoleian, G. The Value of Remanufactured Engines. J. Ind. Ecol. 2004, 8 (1-2), 193−221. (45) U. S. Department of Transportation, Bureau of Transportation Statistics. Transportation Statistics Annual Report, 1994−2012. (46) U. S. Department of Energy, Alternative Fuels Data Center. http://www.afdc.energy.gov/data/categories/vehicles (accessed August 2013). (47) Honda News Releases 2013, Honda Established World’s First Process to Reuse Rare Earth Metals Extracted from Nickel-metal Hydride Batteries for Hybrid Vehicles. http://world.honda.com/news/2013/ c130303Reuse-Rare-Earth-Metals/ (accessed March 2014). 6559
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(48) German Institute for Rare Earths and Metals, Current and Historical Market Prices of the Most Common Rare Earth Metals. http:// institut-seltene-erden.org/en/current-and-historical-market-prices-ofrare-earth-gangigsten/ (accessed August 2013). (49) Metal-pages. http://www.metal-pages.com/ (accessed August 2013). (50) Breslin, M. Domestic shredders starving for feedstock. Am. Recycl. 2011, January, 25,31. (51) Fowler, J. Meatball Separators. Scrap 2011, January/February, 103−106. http://www.scrap.org/ArticlesArchive/2011/JanuaryFebruary/EquipFocusMeatballSeparators.htm (accessed March 2014).
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Value Analysis of Neodymium Content in Shredder Feed: Toward Enabling the Feasibility of Rare Earth Magnet Recycling H. M. Dhammika Bandara, Julia W. Darcy, Diran Apelian, and Marion H. Emmert* Center for Resource Recovery and Recycling, Department of Chemistry and Biochemistry & Department of Mechanical Engineering, 100 Institute Road, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, United States S Supporting Information *
ABSTRACT: In order to facilitate the development of recycling technologies for rare earth magnets from postconsumer products, we present herein an analysis of the neodymium (Nd) content in shredder scrap. This waste stream has been chosen on the basis of current business practices for the recycling of steel, aluminum, and copper from cars and household appliances, which contain significant amounts of rare earth magnets. Using approximations based on literature data, we have calculated the average Nd content in the ferrous shredder product stream to be between 0.13 and 0.29 kg per ton of ferrous scrap. A value analysis considering rare earth metal prices between 2002 and 2013 provides values between $1.32 and $145 per ton of ferrous scrap for this material, if recoverable as pure Nd metal. Furthermore, we present an analysis of the content and value of other rare earths (Pr, Dy, Tb).
1. INTRODUCTION The recent implementation of export restrictions on rare earth (RE) elements and RE containing products by China has resulted in price explosions for these materials in 2011. Manufacturers of hybrid and electric cars, electric motors, actuators, turbines, and hard disk drives in the U.S. and elsewhere have been struggling to cope with unstable prices, as many of these technologies require the RE elements neodymium (Nd), dysprosium (Dy), or samarium (Sm) as raw materials for strong and light magnets.1−3 This issue provides a strong motivation for the United States to invest in methods for price stabilization of REs as critical materials.4 Typical approaches to this end include stockpiling, substitution, and recycling.5,6 However, despite recent efforts, none of these strategies are currently implemented on a large scale.7 Recycling can lessen the impact of external factors on the price and thus aid in stabilizing market prices.8,9 With respect to RE magnets, technologies for the recovery, reuse, and recycling of magnetic scrap and chips generated as waste during manufacturing have already been developed.10 However, no existing commercial process in the U.S. recycles RE magnets from end-of-life products such as used cars and household appliances. Reasons for this, among others, are the lack of data on the quantity of RE materials from magnets in waste streams and on the fate of magnets after shredding.11 Herein, we focus on quantifying the amount of Nd in current (2013) shredder product streams, as NdFeB magnets are the most widely used types of RE magnets and critical materials for the further implementation of sustainable technologies such as wind turbines and electric vehicles. Based on the obtained data, © 2014 American Chemical Society
we further estimate the value of Nd and other REs from magnets that can be recovered through recycling end-of-life cars and household appliances. Since SmCo magnets are typically not used in motors unless durability at high temperatures is required,12 the analysis herein focuses only on NdFeB magnets. Furthermore, SmCo magnets have a much smaller market share than NdFeB magnets, and are thus not expected in substantial amounts in the shredder product stream.13
2. MATERIALS AND METHODS 2.1. Approach. In order to quantify the amount of Nd contained in shredder input and product streams, three variables need to be known: (i) the composition of shredder feed, (ii) the weight percentage of ferrous materials in each source of shredder feed, and (iii) the average weight of Nd in each source. These three variables are treated separately below in order to estimate the Nd content of the shredder feed and the ferrous shredder product stream. Overall, we assume that magnetic materials including RE magnets will be located together with steel in the ferrous output of shredders, as the separation of ferrous materials from nonferrous materials is achieved through a magnetic separation step.14 The part of ferrous scrap found in shredder residue has been considered separately (see SI). Received: Revised: Accepted: Published: 6553
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Figure 1. Lifecycle of Nd magnets between end-of-life product and shredder scrap separation.14,19
Figure 2. (A) Total weight and calculated ferrous materials content (68%) in LDVs. (B) Calculated age distribution of LDVs shredded in 2013. (C) Estimated average weight of Nd mNd,i in a LDV vs year of manufacturing. (D) Calculated weight of Nd in ferrous materials xi from LDVs vs manufacturing year. Vertical axis shows Nd content in g per kg of ferrous scrap.
2.2. Shredder Feed Composition. Typical shredder feed materials include light duty vehicles (LDVs), discarded household appliances, and other sources of steel scrap, such as dismantled bridges, steel from demolished buildings, and discarded railroad cars (Figure 1).14,15 The LDV category consists of passenger cars, passenger vans, sports utility vehicles (SUVs), and light trucks. 16 The category “household appliances” includes only major appliances (refrigerators, washing machines, air conditioners).17,18 The exact composition of shredder feed determines the ratio and the quality of the product streams (e.g., ferrous vs nonferrous scrap) and is thus a closely guarded trade secret of shredder operators. However, average values for shredder feed compositions can be found to be 15−50% household appliances, 40−80% cars, and 10−15% other sources by weight, with the variations reflecting regional availabilities, seasonal variations, and existing materials contracts.14,19 Using these literature data for the ratio of end-of-life products in the feed and information about the ferrous materials content in
each source, we can determine the weight percentage of ferrous materials in the shredder feed (see 2.3). This is crucial, as RE magnets are expected to be located in the ferrous product stream due to their intrinsic magnetic properties. 2.3. Weight Percentage of Ferrous Materials in Scrap Sources. After shredding, ferrous and nonferrous scrap is separated using a drum magnet (Figure 1).14 The nonferrous fraction is further sorted to separate nonferrous metals (zinc, copper, aluminum, brass, and some stainless steel) from nonmetallic materials (plastics, glass, foam and fabrics). The ferrous product is typically the main product of a shredder operation and is sold to steel mills to produce recycled steel.14 The relative amounts of ferrous and nonferrous materials in the overall product streams can be determined by considering the average ferrous content in each source of shredder feed (LDVs, household appliances, and other sources). 2.3.1. Ferrous Content of LDVs. The weight percentage of ferrous materials in LDVs has remained between 65 and 70% since the early 1970s,19−24 despite a significant increase in 6554
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vehicle weight since then (Figure 2A).23 For the calculations herein, we approximate that the average value of 68 weight-% is a good representation of the ferrous materials content of LDVs.24 2.3.2. Ferrous Content of Household Appliances. Major household appliances contain between 25% and 51% of ferrous materials by weight. For the following calculations, we assumed that household appliances contain 40% ferrous materials by weight, which is the calculated average of several reported ferrous materials contents.25−27 2.3.3. Ferrous Content of Other Sources of Scrap. Other sources of scrap include steel beams from dismantled bridges, steel from demolished buildings and railroad cars. These sources consist of almost 100% of ferrous materials;15 thus, we approximate their ferrous materials content to be 100% for further calculations. Based on the approximations above and on the data for the composition of shredder feed, we calculate that the ferrous scrap stream is by far the largest shredder product stream by weight (57−69%; literature values are 60−80%).14,19 2.4. Neodymium Content in Different Scrap Sources. To the best of our knowledge, the Nd content in U.S. shredder scrap has not been determined. Therefore, we use estimates to determine the amount of Nd in the three main components of shredder feed (LDVs, household appliances, and other sources), which are then used to calculate the Nd content in ferrous scrap. 2.4.1. Other Sources of Scrap. As mentioned before, other sources of scrap mainly consist of construction materials and railroad cars.14 We do not expect RE magnets in any of these sources as they typically do not contain electric motors or other magnetic materials. Hence, we assume a Nd content of 0% for other sources of scrap. 2.4.2. Household Appliances. Nd contents of some common household appliances sold in the U.S. have been reported.28,29 However, these data in combination with annual sales data and average lifetimes1,18 are not sufficient to accurately estimate the amount of Nd from all shredded appliances. More accurate data are available for shredded waste electronic and electric equipment (WEEE) in the U.K., for which the Nd content has been experimentally determined to be 0.70 g Nd per 1 kg of ferrous shredder scrap.30 WEEE mainly consist of mixed household appliances (69% by weight) such as refrigerators (containing 40−60 g NdFeB magnets per unit), washing machines (80−180 g NdFeB/unit), and air conditioners (60−400 g NdFeB/unit).29,31 When adjusting the average value for the Nd content (0.70 g Nd/kg ferrous scrap) for contributions from electronics8,32 and other materials present (e.g., lighting equipment; for the calculations see the SI), a value of 0.61 g Nd per kg ferrous scrap can be derived for major household appliances. The original value (0.70 g Nd/kg ferrous scrap) as well as the adjusted value (0.61 g Nd/kg ferrous scrap) will both be used in final calculations of the Nd content in ferrous scrap. We postulate that the data derived from U.K. WEEE are a good approximation for the Nd content in household appliances shredded in the U.S. This hypothesis is based on several similarities between the U.S. and the U.K. recycling enterprise. First and foremost, the collection of household appliances is nonmandatory in both countries, unlike in most other European nations.29,30 Second, both nations are among the most developed countries in the world, which can be documented by different metrics such as the 2012 gross
national income per capita ($43,480 for the U.S.; $32,538 for the U.K.),33 the 2012 human development index (0.94 out of 1 for the U.S.; 0.88 for the U.K.),33 and the 2011 gross average monthly wage ($4538 for the U.S.; $4199 for the U.K.).34 Third, according to data released by the U.S. Association of Home Appliance Manufacturers and the City of York recycling facility (U.K.), household appliances to be recycled in both countries are of very similar average weight (58−63 kg/unit for the U.S.; 56 kg/unit for the U.K.).35−37 Based on these data, we postulate that the value of 0.70 g/kg ferrous scrap derived from studies in the U.K. as well as the calculated value of 0.61 g Nd/ kg ferrous scrap are good assumptions for the Nd content of ferrous scrap from U.S. household appliances. Both values will be used below to calculate the total Nd content in the ferrous scrap stream in dependence on the shredder feed composition. 2.4.3. LDVsGeneral Approach. Arriving at a good approximation for the Nd content in shredded LDVs is challenging because currently shredded LDVs have been manufactured over a broad range of years. During this time, the weight of LDVs and their ferrous materials content has changed significantly as discussed before (see Figure 2A). Additionally, changes in the Nd content of the vehicles during this period have occurred because NdFeB magnets have only been introduced to the market in 1984.38 Thus, an increase in the amount of Nd in vehicles manufactured in the last decades seems likely, as the electrification of vehicles and, with it, the use of magnets in speakers and various types of motors has steadily progressed.39 Therefore, the age distribution of LDVs, the weight of Nd in shredded LDVs, and the weight of ferrous materials all need to be calculated to approximate the Nd content in currently shredded LDVs. The age distribution of LDVs can be expressed as a series of values wi, which stand for the percentage-wise contribution of vehicles manufactured in year i to the overall population of currently shredded LDVs. Additionally, values xi for the amount of Nd in ferrous scrap from shredding LDVs manufactured in year i need to be known. With these variables, the average Nd content in ferrous scrap x̅ can be calculated using the average mean method (eq 1). The values of xi can be determined using eq 2 and the variables mNd,i (the average weight of Nd in an LDV produced in year i) and mferrous,i (the weight of ferrous materials in an LDV produced in year i).
x̅ = xi =
∑ wx i i ∑ wi
(1)
mNd, i mferrous, i
(2)
2.4.3.1. Age Distribution of Shredded LDVsDetermining wi. No data is available on the age distribution of LDVs shredded at present in the U.S. However, the age distribution of LDVs shredded in 1995 in the U.S. has been reported.40 This distribution is best described by a Weibull distribution function (eq 3), in which wi is the percentage of LDVs manufactured in a previous year i that makes up the population of LDVs being shredded at present. ⎛ i−i ⎞ −⎜ 0 ⎟ α wi = 100 × α (i − i0)α − 1e ⎝ β ⎠ β
α
(3)
This function and with it the parameters wi are determined by the manufacturing year i, the oldest manufacturing year in the distribution i0, and the mean lifetime of LDVs. In 6555
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vehicles manufactured between 1985 and 2012, using an approximation of 68% for all our calculations as discussed in section 2.3.1 (see also Figure 1). 2.5. Nd Content in Ferrous ScrapDetermining xi and x.̅ By substituting the values for the weight of ferrous materials mferrous,i and the total weight of Nd in an LDV mNd,i in eq 1, the weight percentage xi of Nd in ferrous scrap from LDVs manufactured in year i can be calculated (see Figure 2D). For example, a typical LDV built in 2000 weighs 1732 kg. Ferrous materials account for 68% of this weight and thus mferrous,2000 equals 1178 kg (68% × 1732 kg). The weight of Nd mNd,2000 in the LDV is 134 g; therefore, the Nd content in ferrous scrap x2000 which is produced by shredding this average LDV is 0.11 g/kg (134 g/1178 kg). By entering all the obtained values for xi and wi into eq 2, the Nd content in the part of ferrous scrap that is generated through shredding LDVs was calculated to be on average 0.10 g per kg ferrous scrap (for detailed calculation and tabulation of xi and wi see the SI).
agreement with the literature, we assume for our calculations that the oldest shredded vehicles in the LDV population are 28 years old and that the mean lifetime is 13 years.20,41 With these assumptions, the parameters α and β are two empirical constants that have been determined to fit the Weibull distribution to the observed data; literature precedent suggests values of α = 7.3 and β = 14.8 to be a good fit, which will be used for further calculations.41 Adapting the Weibull distribution function to estimate the age distribution of LDVs shredded in 2013 then leads to an age distribution as shown in Figure 2B. Interestingly, a large majority (nearly 75%) of LDVs that are shredded at present have been manufactured in the short time span between 1997 and 2001. Therefore, we expect that the amount of Nd in cars built during these 5 years will be crucial for the Nd content in scrap generated in 2013 from shredding LDVs. More recent data on the age distribution of shredded cars in Connecticut from 2007 confirm that the Weibull distribution discussed above is still valid for approximating the age distribution of today’s shredded LDVs.40 The mean age of cars determined by this more recent publication is 16 years, which is very similar to the function used above (13 years). At the same time, the oldest shredded cars in 2007 were shown to be 30 years old, which is very close to the age of the oldest cars assumed above (28 years). Since both distributions show slightly different values, the Nd content in the ferrous shredder stream has been calculated for both distributions (see below and SI). The effect of using different age distributions on the Nd content and the value analysis will be discussed in the Results and Discussion section. 2.4.3.2. Total Weight of Nd in LDVs − Determining mNd,i. In order to determine mNd,i (the Nd content of a vehicle produced in year i) we use the only available literature data on the Nd content of average LDVs manufactured in the years 2012 and 1995. Kirchain and co-workers have determined the total amount of Nd in the 11 most common motors of a typical 2012 model year sedan to be 173 g per car, which allows us to estimate the average amount of Nd to be 16.3 g per motor (173 g/11).42 Fastenau and Loenen report that LDVs manufactured in 1995 contain on average 60 motors and that 7% of these motors contain NdFeB magnets.43 Using the same value as above for the average weight of Nd in a motor (16.3 g), the total amount of Nd in a typical LDV manufactured in 1995 was calculated to be 68.5 g (7% × 60 motors × 16.3 g). Next, we assume that the total amount of Nd in an LDV increased linearly over the years with the stepwise incorporation of NdFeB magnet technology. This approach provides the total weight of Nd in a car in dependence on its year of manufacturing (Figure 2C). According to our estimates, no Nd from NdFeB magnets should be present in cars built prior to 1989. This is, in our opinion, supported by data for the market share of NdFeB magnets in 1988, which is 0.14% of the total number of magnets produced globally.44 Because these magnets were discovered only in 1984,38 both their low market share and the lack of their incorporation in LDVs seem reasonable. 2.4.3.3. Weight of Ferrous Materials in LDVs − Determining mferrous,i. The average weight of LDVs in the U.S. has increased from 1483 to 1841 kg between 1985 and 2005, and remained relatively constant since 2005. However, the weight percentage of ferrous materials in LDVs has remained between 66 and 70% of the total weight since 1985.22 This allows us to calculate the weight of ferrous materials in
3. RESULTS AND DISCUSSION 3.1. Quantifying Nd in Ferrous Scrap. Our estimates of the Nd and ferrous materials content in each scrap source and the literature-known ranges of shredder feed composition (40− 80% LDVs, 15−50% household appliances, and 10−15% other sources)14,19 allows us to quantify the amount of Nd in ferrous shredder scrap produced in 2013. Household appliances contain the largest amount of Nd per weight of ferrous scrap (0.70 g per kg of ferrous scrap); in comparison, the Nd content in shredded LDVs is much lower (0.10 g per kg of ferrous scrap) and other sources (railroad cars, dismantled bridges etc.) do not contain any Nd. Therefore, we expect that a shredder feed with the largest amount of household appliances and the smallest amount of other sources contains the maximum amount of Nd. Consequently, the minimum amount of Nd is present in a shredder feed with a minimum amount of household appliances and a maximum amount of other sources. Both of these cases are discussed below in detail. Maximum Nd Content. The weight percentage of household appliances in shredder feed does not exceed 50% and, at the same time, the minimum weight percentage of other sources cannot be less than 10%.14 Therefore, a shredder feed consisting of 50% household appliances, 40% cars, and 10% other sources will produce ferrous scrap with a maximum Nd content. Based on our calculations, the total amount of Nd can thus be estimated to be 167 g/572 kg = 0.29 g/kg ferrous scrap under these conditions (see Table 1). Minimum Nd Content. In analogy, the Nd content in ferrous scrap will be minimized using a shredder feed Table 1. Maximum Nd Content in Ferrous Scrapa
scrap source household appliances LDVs other sources total a
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% of total scrap feed
% ferrous in source
ferrous scrap per 1000 kg shredder feed
Nd content per kg ferrous scrap by source
weight of Nd in 1000 kg shredder feed by source
50%
40%
200 kg
0.70 g
140 g
40% 10%
68% 100%
272 kg 100 kg
0.10 g 0g
27 g 0g
572 kg
167 g
All percentage values are weight-%. dx.doi.org/10.1021/es405104k | Environ. Sci. Technol. 2014, 48, 6553−6560
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parts, no processes are operational yet. However, due to the considerable Nd content in hybrid vehicles, we expect that the Nd content of shredder feeds in the future can be influenced significantly when a high market penetration is achieved. 3.3. Value of REEs in Ferrous Scrap. Importantly, with our calculations of the minimum and maximum content of Nd in ferrous shredder scrap, we are now able to determine the respective value of the recoverable REs. This is crucial, as the establishment and continuous use of practical recycling technologies for RE magnets is dependent on their commercial feasibility. Additional separation, isolation and purification steps will be required to recover pure Nd from ferrous scrap. Thus, the materials values calculated herein can only be one of the factors that need to be considered for establishing new recycling technologies. Value of Nd. For the following value calculations, Nd prices were based on the market prices for pure Nd from the German Institute for Rare Earths and Metals.48 In order to gain a better insight into the possible price ranges, we have considered (i) the maximum price of Nd ever observed (August 2011; $500/ kg), (ii) the minimum price of Nd from the 10 year period before the price spike (August 2002; $12.00/kg), and (iii) current pricing from August 2013 ($95/kg; Table 3).49 Furthermore, we have tabulated both the maximum (0.29 g per kg) and minimum (0.13 g per kg) Nd content in ferrous scrap, which is dependent on the composition of shredder feed, as discussed above. Using this approach, we estimate that 1 t of ferrous scrap contains Nd with a value between $1.56 and $145. In analogy, the value of Nd in the ferrous product stream of smaller shredders processing 2000−3000 t per month50 (∼75% ferrous scrap14) can be estimated to be between $2340 and $326,250 (Table 3). With modified (see SI) values (age distribution of shredded LDVs from 2007; adjusted Nd content of major household appliances), price ranges of $1.32 to $140 per ton of ferrous scrap ($1980 to $315,000 per monthly output of smaller shredder) are obtained in analogous calculations, which are in the same order of magnitude as the above discussed values. Value of Other RE Elements. Due to the similar chemical reactivities of the rare earth elements, a recovery process for Nd from magnets would most likely also recover any other rare earth metals present in magnets. For example, NdFeB magnets can contain up to 9% of other RE elements such as dysprosium (Dy), terbium (Tb), and praseodymium (Pr) in addition to Nd.6 Our calculations above enable us to estimate the maximum amounts of these elements that might be present in the recovered mixture of rare earth elements and to estimate a maximum value for the present amounts. Prices for Pr are typically lower than for Nd, and manufacturers have added Pr to RE magnets during times of high prices for Nd in order to lower production costs.8 Since Pr is added in very small quantities (≤5% of the weight of Nd) the
composition with the lowest possible weight percentage of household appliances and the highest possible weight percentage of other scrap sources. This estimation results in a shredder feed composition of 15% household appliances, 15% other sources, and thus 70% LDVs, providing a minimum Nd content of 90 g/686 kg = 0.13 g/kg ferrous scrap (see Table 2). Table 2. Minimum Nd Content in Ferrous Scrapa
scrap source household appliances LDVs other sources total a
% of total scrap feed
% ferrous in source
ferrous scrap per 1000 kg shredder feed
Nd content per kg ferrous scrap by source
weight of Nd in 1000 kg shredder feed by source
15%
40%
60 kg
0.70 g
42 g
70% 15%
68% 100%
476 kg 150 kg
0.10 g 0g
48 g 0g
686 kg
90 g
All percentage values are weight-%.
Analogous calculations have been performed (see SI) using (i) an age distribution of shredded cars from 2007;40 (ii) an adjusted value for the Nd content of household appliances; and (iii) using both of these modifications in our Nd content calculations. The results are close to the above-discussed outcomes and provide ranges of 0.11 to 0.28 g Nd per kg ferrous scrap. Due to these very close results we will use the original values of 0.13 to 0.29 g Nd per kg ferrous scrap to discuss exemplary price calculations further below. Analogous price calculations for the modified Nd content values are provided in the SI. 3.2. Influence of Hybrid and Electric Vehicle Use on Nd Content. One factor that could substantially influence the Nd content in shredded LDVs is the presence of electric and hybrid vehicles in the shredder feed. According to Kirchain, a typical hybrid car with a NiMH battery contains approximately 3.2 kg of Nd. 2.4 kg of Nd are located in the battery which is removed prior to shredding, but the remaining amount of Nd (0.80 kg) is still significantly higher than the Nd content in a typical conventional car (0.29 kg).34 Most cars that constitute the LDVs in shredder feed in 2013 were manufactured between 1998 and 2001 (see Figure 2B above). In 2000, hybrid and electric vehicles accounted for only 0.10% of car sales in the U.S., which we assume to be a good estimate of sales for the years between 1998 and 2003.45,46 Due to this very low number, we conclude that the presence of hybrid and electric vehicles has a negligible influence on the Nd content in ferrous scrap for today’s shredder operations, especially since most of these vehicles are currently not sent to shredders as only one process for the recovery of REs from NiMH batteries has been established.47 For other precious
Table 3. Minimum and Maximum Values of Nd Content in Ferrous Scrap Nd market price49 $12/kg Nd (August 2002) $500/kg Nd (August 2011) $95/kg Nd (August 2013)
Nd content per kg ferrous scrap 0.13 0.29 0.13 0.29 0.13 0.29
g g g g g g
value of Nd per ton ferrous scrap
value of Nd in ferrous scrap output (1500−2250 t) of smaller shredder per month50
$1.56 $3.48 $65.00 $145.00 $12.35 $27.55
$2340 to $3510 $5220 to $7830 $97,500 to $146,250 $217,500 to $326,250 $18,525 to $27,788 $41,325 to $61,988
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Environmental Science & Technology value of Pr in ferrous scrap is estimated to be much lower than that of Nd ($3.75 per ton of ferrous scrap; Table 4).
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Table 4. Value of Rare Earth Elements other than Nd in Ferrous Scrap
The Supporting Information includes detailed calculations of the Nd content in LDVs. This material in available free of charge via the Internet at http://pubs.acs.org.
rare earth element
maximum price per kg in 201149
maximum weight per ton of ferrous scrapa
maximum value of rare earth elements per ton of ferrous scrap
Pr Dy Tb
$250 $3100 $5000
0.015 kg 0.015 kg 0.015 kg
$3.75 $46.50 $75.00
Policy Analysis
ASSOCIATED CONTENT
S Supporting Information *
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AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected]. Notes
The authors declare no competing financial interest.
a
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Based on the maximum weight of Nd per ton of ferrous scrap 0.29 kg × 5 weight-% = 0.015 kg.
ACKNOWLEDGMENTS This work was supported by WPI, NSF (IIP-0968839) and the members of the I/U CRC Center for Resource Recovery and Recycling (CR3). We thank all members of CR3 for valuable discussions. In particular, we acknowledge Jeff Webster (previously wTe, now Victaulic Corp.), Mark Bauer (GM), Yan Wang (WPI), and Jerry Schaufeld (WPI) for their valuable input.
Dy and Tb are added to NdFeB magnets to increase the operating temperature window of the magnets. Both elements are significantly more expensive than Nd, and are thus preferentially added in very small quantities. As such, the Dy content found in magnets for motors is typically not higher than 5%.6,8 If all NdFeB magnets are assumed to contain 5% of Dy, the maximum value of recoverable Dy per ton of ferrous scrap is $46.50, based on the highest historic Dy prices in 2011. In analogy, if 5% Tb is used in all magnets instead of Dy, the maximum value of recoverable Tb is $75.00. However, not all NdFeB magnets contain 5% of Dy or Tb. Therefore, the actual value of Dy and Tb in ferrous scrap is expected to be typically much lower than these estimated maximum values.
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ABBREVIATIONS B boron Co cobalt Dy dysprosium Fe iron HVAC heating, ventilation, and air conditioning LDV light duty vehicle Nd neodymium NiMH nickel metal hydride Pr praseodymium RE rare earth(s) REE rare earth element(s) Sm samarium Tb terbium WEEE waste electronic and electric equipment
4. SUMMARY AND CONCLUSIONS In summary, we have estimated the content of Nd in ferrous scrap shredded in 2013. Based on the lifecycle of end-of-life light-duty vehicles (LDVs) and household appliances, we have estimated a maximum and minimum Nd content in ferrous shredder scrap (0.13 and 0.29 g of Nd per kg of ferrous scrap). Furthermore, we have considered the influence of the presence of hybrid and electric vehicles in the relevant waste streams. Using historical and current market prices, we were able to estimate the value that could be generated by recovering Nd and other rare earth elements from the ferrous scrap product stream. The value of recoverable Nd varies greatly between $1.32 and $145 per ton of ferrous scrap, reflecting the large price fluctuations between 2002 and 2013. In contrast, the used age distribution of shredded cars and modifying the Nd content of major household appliances have only a minor effect on the value analysis. The model calculations used herein are flexible to accommodate changes in the waste streams that are expected for the future−for example, when hybrid and electric vehicles reach a higher market penetration. We expect that the results of our analysis will be one factor that helps to determine the feasibility of recycling and recovery technologies for rare earths from end-of life magnets. However, before recycling of end-oflife rare earth magnets will become a reality many challenges11 still need to be addressed: (i) Identification of the RE containing shredder product stream(s) (e.g., steel scrap or copper pickings);51 (ii) development of sortation technologies that accumulate RE containing materials in real time; (iii) selective leaching of RE contents; (iv) separation and recovery of REs. Creating such technologies in a sustainable and economically sound fashion is the focus of our future work in this area.
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