Material Flow Analysis of NdFeB Magnets for Denmark - American

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Material Flow Analysis of NdFeB Magnets for Denmark: A Comprehensive Waste Flow Sampling and Analysis Approach Komal Habib,*,† Peter Klausen Schibye,† Andreas Peter Vestbø,‡ Ole Dall,† and Henrik Wenzel† †

Department of Chemical Engineering, Biotechnology and Environmental Technology, University of Southern Denmark, Niels Bohrs Alle 1, DK-5230 Odense M, Denmark ‡ Teknologisk Institut, Gregersensvej 7, DK-2630 Taastrup, Denmark S Supporting Information *

ABSTRACT: Neodymium−iron−boron (NdFeB) magnets have become highly desirable for modern hi-tech applications. These magnets, in general, contain two key rare earth elements (REEs), i.e., neodymium (Nd) and dysprosium (Dy), which are responsible for the very high strength of these magnets, allowing for considerable size and weight reduction in modern applications. This study aims to explore the current and future potential of a secondary supply of neodymium and dysprosium from recycling of NdFeB magnets. For this purpose, material flow analysis (MFA) has been carried out to perform the detailed mapping of stocks and flows of NdFeB magnets in Denmark. A novel element of this study is the value added to the traditionally practiced MFAs at national and/or global levels by complementing them with a comprehensive sampling and elemental analysis of NdFeB magnets, taken out from a sample of 157 different products representing 18 various product types. The results show that the current amount of neodymium and dysprosium in NdFeB magnets present in the Danish waste stream is only 3 and 0.2 Mg, respectively. However, this number is estimated to increase to 175 Mg of neodymium and 11.4 Mg of dysprosium by 2035. Nevertheless, efficient recovery of these elements from a very diverse electronic waste stream remains a logistic and economic challenge.

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INTRODUCTION Invented first in 1983, NdFeB permanent magnets have now become indispensable for modern hi-tech applications, because they are hard to substitute without any performance loss. The chemical composition of these magnets is Nd2Fe14B (neodymium−iron−boron), and they are more often called neodymium magnets. These magnets are 60 times stronger (as per weight) than the earliest developed permanent magnets in the 1910s. NdFeB permanent magnets are currently used in a wide array of applications ranging from information technology (IT) and telecommunication products, e.g., mobile phones, cameras, tablets, and laptop and desktop computers, to home appliances, such as refrigerators, air conditioners, vacuum cleaners, washing machines, and dryers, as well as clean energy technologies, e.g., hybrid and electric vehicles and wind turbines. The magnetic strength of these magnets has allowed for considerable size reduction maintaining the high performance level, which in our daily life can be visualized in the case of © 2014 American Chemical Society

IT applications, such as mobile phones, tablets, and laptop computers.1−3 What makes these magnets so strong is the presence of rare earth elements (REEs), such as neodymium (Nd), which is present in all of the NdFeB magnets as their name suggests. Usually, praseodymium (Pr) is also found in these magnets because it coexists with neodymium in the geological resources of REEs. Dysprosium (Dy), a heavy REE, is added in small amounts to prevent these magnets from demagnetization at elevated temperatures. Occasionally, praseodymium and terbium (Tb) are used in these magnets to substitute neodymium and dysprosium, respectively. In 2010, NdFeB magnets alone comprised 20% of the total REEs demand, and Received: Revised: Accepted: Published: 12229

April 22, 2014 September 17, 2014 September 19, 2014 September 19, 2014 dx.doi.org/10.1021/es501975y | Environ. Sci. Technol. 2014, 48, 12229−12237

Environmental Science & Technology

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life-cycle stages, namely, mine production, manufacturing (into products), use and maintenance, and disposal. Because the spatial boundary of the current study is confined to Denmark, where neither any mine production nor magnets manufacturing happens, we have divided this MFA into four stages: imports, use, waste management, and exports. Data collection for all of these steps is explained in the next section. The baseline year for this MFA study is 2012 because of the maximum data availability. However, we have made an effort to make a dynamic MFA by projecting the study until 2035. The aim is to present the dynamic behavior of our stock and flow model for the defined time period, i.e., 2012−2035, as well as to include proper estimations of the secondary supply potential of neodymium and dysprosium from recycling of NdFeB magnets, because we need to extend the temporal scope beyond the lifetimes of the essential end-use products containing NdFeB magnets to allow for the modeling of recovered flows in the MFAs. The outflows to calculate the amount of neodymium and dysprosium appearing in the waste stream have been estimated by applying the average lifetimes of all of the different product types (see Table 2), where all of the products are supposed to leave the in-use stock at the end of their average lifetime and enter the waste stream. This approach of applying average lifetimes, as opposed to using lifetime distributions, was judged to provide a sufficient degree of detail for the aim of the study. The same approach has been applied by a number of other dynamic MFA studies reported in the literature.14 In-use stocks can be mainly estimated in two different ways, i.e., by a top-down or a bottom-up approach.14,15 In this study, the top-down method refers to the estimation of in-use stocks based on the calculation of mass balances of the material flow into use with the help of trade statistics and/or country-specific input−output data and the material flow out of use at the end of the product’s lifetime. The bottom-up approach considers estimating the amount of material in the end-use products by detailed waste flow sampling and chemical characterization or using product composition data and combining it with the total number of products in the given geographical boundary. In the current study, both approaches are used to estimate the in-use stocks of neodymium and dysprosium contained in NdFeB magnets because they complement each other by filling in the data gaps. The waste flow sampling and analysis (bottom-up approach) can provide detailed knowledge of the composition of NdFeB magnets regarding their neodymium and dysprosium contents contained in different end-use products. However, because these magnets are mainly found in very recent products, many such products containing NdFeB magnets do not yet appear in the current waste electrical and electronic equipment (WEEE) streams, and obtaining access to new products for further chemical analysis is difficult and can become expensive if proven necessary to buy new products for detailed chemical characterization. Also, some key products, e.g., wind turbines and magnetic resonance imaging (MRI) machines, which are very large-scale end-users of REEs cannot be bought for obvious reasons to perform such chemical analyses. The topdown approach, therefore, becomes important here to complement the bottom-up approach in view of estimating the in-use stocks. The computer software tool STAN (substance flow analysis), developed at Vienna University of Technology, is used for the programming purpose of this MFA study.16

this share is expected to grow rapidly in the future because of the forecasted high demand by different end-use sectors.4,5 REEs are not as rare as their name suggests, because the geological resource of these elements is adequate enough to meet the demand for at least the next couple of hundred years. However, there are risks attached to the supply of REEs because more than 85% of the current global supply originates from China. Simultaneously, China is blessed with 53% of Nd and 72% of Dy known reserves currently. In the past, China reduced the exports of REEs significantly by introducing an export quota in 2005. This resulted in skyrocketed prices of REEs in 2010, which forced the global community to seek other solutions, such as other countries opening new mines, substituting REEs with other elements having less supply risk, and enhancing recycling of REEs from the end-of-life products because their current recycling rate is less than 1%.6,7 More recently, REEs have been classified as critical resources because of the high risk associated with their supply along with their increasing importance in some of the key end-use sectors, such as clean energy technologies.8,9 Du and Graedel10 have presented estimates of the in-use stocks of NdFeB magnets at the global level, where they have considered the same magnet composition for all of the end-use products. A challenge is that, in general, very little information is available regarding the NdFeB magnets and their composition in different end-use products, and the resulting material flow analysis (MFA) studies of resource flows in these magnets, therefore, depend upon rough estimates and imply large uncertainties. As an example, two recently published studies are based on the estimate/assumption that no dysprosium is used in the hard disk drives (HDDs) contained in computers,11,12 an assumption that our more detailed study now shows not to be in line with reality. This study, thus, aims to contribute to qualifying the existing estimation-based MFAs of critical resources in NdFeB permanent magnets by a comprehensive sampling and analysis program of these magnets in the waste flows of the Danish waste management system. The study, therefore, adds value to the already existing literature by providing the detailed REE composition and the weight of NdFeB magnets used in various end-use products. It is aimed at mapping the current (2012) and projecting the future (until 2035) flow of NdFeB magnets in Denmark with the help of the MFA approach to estimate the flows, in-use stocks, and maximum theoretical recovery potential (equivalent to the amount of neodymium and dysprosium contained in the NdFeB magnets present in the waste flows) of these magnets and thereof neodymium and dysprosium from the end-of-life products. This contribution presents the detailed MFA results for 2012 along with the developments in imports, change in stock, waste, and exports of neodymium and dysprosium contained in the NdFeB magnets until 2035, whereas the comprehensive MFA results for 2035 are shown in the Supporting Information.

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MATERIALS AND METHODS MFA. To estimate the current and future (2035) flows and stocks, MFA has been used. MFA has become a widely accepted tool for environmental, waste, and resource management and is defined as the systematic assessment of flows and stocks of materials within a system defined in space and time. A basic principle of MFA is the conservation of matter, where input is equal to output plus any change in stock.13 Usually, MFA of elements/metals comprises four important material 12230

dx.doi.org/10.1021/es501975y | Environ. Sci. Technol. 2014, 48, 12229−12237


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Table 1. Summarized Results of Dismantling and Chemical Analysisa Dismantling Results HDDs (3.5 in.) number of product samples device mass (g) NdFeB mass (g) NdFeB/device (%, w/w)

mobile phones

DVD players

61 553.9 ± 97.4 12.5 ± 6.9 2.2 ± 1.0

31 115.0 ± 38.7 3.4 ± 1.8 2.9 ± 0.5 Elemental Analysis Results

17 120.1 ± 27.2 0.7 ± 0.1 0.6 ± 0.1

5 4000 ± 100 1.429 ± 0.675 0.04 ± 0.02

118 4.6 ± 3.7 30.8 ± 4.1 1.6 ± 1.0

49 4.0 ± 3.2 30.4 ± 3.1 2.4 ± 1.0

17 8.7 ± 0.8 27.5 ± 1.6 1.3 ± 0.9

number of magnet samples Pr/magnet (%, w/w) Nd/magnet (%, w/w) Dy/magnet (%, w/w) Tb/magnet (%, w/w)b

HDDs (2.5 in.)

5 0.2 ± 0.3 35.1 ± 3.2 3.3 ± 1.8

a

HDD (3.5 in.), hard disk drive for a desktop computer; HDD (2.5 in.), hard disk drive for a laptop computer; DVD, digital video disc; and w, weight. bTerbium (Tb) was analyzed in all samples with the help of EDX spectroscopy, where the detection limit of the EDX equipment is 0.1% (w/ w), but in all cases, the content of Tb was found to be below the detection limit.

Table 2. List of Products Having NdFeB Magnets and Their Average Lifetimea magnet composition (%)

product category power medical devices automobiles

home appliances

body care appliances IT and telecommunication

miscellaneous

product wind turbines (1 MW) MRI conventional vehicles

average lifetime (years)

average weight of the magnet (kg/unit)

neodymium (Nd)

dysprosium (Dy)

25b

660b

30b

2b

1010 16c

86025 1.14 until 2011 1.72 from 201226,d same as a conventional vehicle +2 kg of magnet for the motor/generator system6,8,26,d 1.04e 0.54e 0.49 (freezer)e 0.26 (fridge)e 0.5e 0.09 (standard)e 0.08 (robotic)e 0.11e 0.001e 0.001g 0.0125g 0.0034g 0.0034e 0.0034e 0.0014g 0.0015e 0.0007g 0.055 (circulator pumps)h

2125 2926,d

1.6325 226,d

same as a conventional vehicle +31% Nd for the motor/generator system6,8,26,d 29e

same as a conventional vehicle +6% Dy for the motor/generator system6,8,26,d e 2

30e 30g 30.8g 30.4g 30.4e 30.4e 35.1g 29e 27.5g 25 (circulator pumps)h 29 (others)e

2e 2.3g 1.6g 2.4g 2.4e 2.4e 3.3g 2e 1.3g 0.05 (circulator pumps)h 2 (others)e

electric and hybrid vehicles

1611

washing machine dryer refrigerator

1123 1223 1223

air conditioner vacuum cleaner

1023 723

microwave oven electric toothbrush body shavers desktop computer laptops notebook tablet DVD players speakers mobile phones circulator pumps, industrial applications, etc.

823 223 423 1011 611 4f 3f 5f 1010 3f 20h,f

a

MW, megawatt; MRI, magnetic resonance imaging; IT, information technology; and DVD, digital video disc. bConfidential data from a leading wind turbine manufacturer. cLifetime of conventional vehicles assumed the same as electric vehicles.11 dConfidential data from a leading car manufacturer and a major REE mining company. eInformation provided by a leading home appliance producer and magnet manufacturer. fLifetimes of products assumed based on expert opinion and industrial sources. gResults obtained from our own chemical analysis of NdFeB magnets. h Confidential data from a leading circulator pump manufacturer.

Waste Flow Sampling, Dismantling of WEEE, and Chemical Characterization of NdFeB Magnets. In this study, we have targeted 7 different general product categories ranging from personal care products to electricity generators. Within these 7 product categories, a total of 18 different product types were dismantled, falling mostly into the product categories of IT, home appliances, and personal care products.

Altogether, a total of 157 products were dismantled, with their magnets taken out and analyzed (see section S1 of the Supporting Information for more details). All dismantling of WEEE was performed manually using ordinary hand tools: screwdrivers, hammer, chisel, clamp, universal pliers, etc. The magnets were first demagnetized by thermally treating them in an oven at 400 °C for 45 min. After cooling to room 12231



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Figure 1. MFA of neodymium contained in NdFeB magnets (Mg year−1) for Denmark in 2012, where the process boxes show the in-use stock + Δ stock for the specific product category. dStock, Δ stock; EoL, end-of-life; IT, information technology; DVD, digital video disc; and MRI, magnetic resonance imaging.

and composition in Table 1. The detailed data for the dismantled HDDs regarding their NdFeB magnet mass, REE composition, and the correlation between the REE consumption of the HDDs and their year of manufacturing can be found in the section S2 of the Supporting Information. Table 2 presents the average lifetimes, NdFeB magnet weight, and composition for 20 different product types considered in this study.

temperature, the nickel (Ni) coating on the magnets was peeled off manually to reveal a fresh surface of the magnet material. The thickness of nickel coating was measured as 50 ± 10 μm. A field emission Zeiss XB-1540 scanning electron microscope equipped with an energy-dispersive X-ray (EDX) spectroscopy system17,18 was then used for elemental identification of the magnet material. The dismantled WEEE items, which have been chemically characterized to know their NdFeB magnet composition are summarized regarding their magnet weight 12232



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Data Collection and Assumptions. With regard to the top-down approach for the in-use stock estimation, the United Nations Comtrade database is used for the estimation of annual imports and exports of NdFeB magnets, where the representative categories for permanent magnets are HS 850511 and HS 850519.19,20 These data, further, have been cross-checked with different industries, e.g., the circulator pump and wind turbine manufacturers in Denmark, who import the NdFeB magnets/magnet alloy to produce the final goods. The Euromonitor International database is used to estimate the number of products containing NdFeB magnets sold in Denmark from 2006 to 2012.21−23 The data regarding the number of MRI machines, direct-drive wind turbines, and passenger vehicles (both conventional and electric) in Denmark have been obtained from the relevant administrative and industrial sources. As mentioned above, seven different product categories ranging from body care appliances to electricity generators have been chosen, which further correspond to 20 different end-use products (Table 2). Data collected from industry and research organizations were used regarding the magnet weight and its composition for the products that could not be dismantled and chemically characterized in detail. This information later supplemented the bottom-up approach to estimate the in-use stock in different product categories. All of the assumptions made for this study are documented in section S3 of the Supporting Information. To perform the dynamic MFA of NdFeB magnets in Denmark by 2035, we have projected the sales or technology deployment data for all of the product categories considered in this study until 2035. The Euromonitor International database has been used regarding the market forecasts of IT application and mobile phones by 2016 and the personal care products and consumer appliances by 2017.21−23 After 2016 (for IT applications and mobile phones) and 2017 (for the personal care products and consumer appliances), we have developed a historical trend-based projection of these product categories until 2035. To estimate the number of passenger vehicles by 2035, we have adapted the data from Danish Statistics24 and modified it to calculate the annual sales of passenger vehicles until 2035, where the share of electric and hybrid vehicles has been projected on the basis of their historical development trend. For the MRI machines, we have used their historical development trend to project the future number of annually installed MRI machines up to 2035. The future deployment rate of direct-drive wind turbines has been estimated on the basis of the assumption that all of the offshore wind turbines installed in the future will be direct-drive turbines having NdFeB magnets, where the forecasts related to the number of annual installed offshore turbines until 2035 have been obtained from industrial sources. The NdFeB magnet demand by the miscellaneous category has been projected until 2035 based on a historical trend-based projection along with expert opinion from industrial sources. With regard to the weight of NdFeB magnets and their chemical composition, we have assumed the same data by 2035 as we have used for the current estimations (2012) for all of the product categories, except for passenger vehicles, where we have assumed an increase in REE consumption by almost 33% because of the increase in the number of electric motors from 2012 onward (on the basis of confidential data provided by a major REE mining company and a leading vehicle manufacturer). The assumptions regarding the share of products having NdFeB magnets in

various product categories can be found in section S3 of the Supporting Information. Uncertainty Analysis. Because of the inherently uncertain nature of MFA results arising because of data availability and quality concerns along with the diverse nature of data sources, it becomes highly important to address the uncertainty of MFA results in a systematic manner.27 In the case of rich data availability, uncertainty of the input data for normally distributed variables can be shown with the help of traditional statistics and defined as the mean value ± 2 standard deviations, which correspond to an approximately 95% confidence interval (x ± y). However, because of the nature of the current study, where the lack of empirical data is the obvious issue, we have performed the data uncertainty analysis based on the method proposed by Hedbrant and Sörme.28 The details of the uncertainty analysis carried out in this study can be seen in section S4 of the Supporting Information.

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RESULTS AND DISCUSSION MFA of NdFeB Magnets in Denmark, 2012. MFA is used as a tool to quantify the in-use stocks as well as the maximum theoretical recovery potential of individual REEs (neodymium and dysprosium) present in NdFeB magnets contained in different end-use products from 2012 to 2035. Because no mining and refining of REEs occurs in Denmark, the flow of NdFeB magnets starts from the import of products containing these magnets and the magnets/magnet alloy, which is further used in different end-use products (named as the miscellaneous category in this study, containing products, e.g., industrial motors, circulator pumps, toys, magnetic bike lights, etc.). Results presented in Figure 1 regarding the neodymium MFA in Denmark for the year 2012 reveal that a total of 283 ± 36.5 Mg of neodymium, equivalent to almost 1% of the global neodymium mine production in 2010, was imported to Denmark mainly in two forms: first, magnets and magnet alloy to be further used in end-use products i.e., wind turbines and miscellaneous category; second, final products containing NdFeB magnets, such as IT applications, home appliances, etc. The major import category for neodymium is the wind turbine category, which alone is responsible for 46% of total import in 2012. However, it is important to mention that, out of this, almost 80% is currently used in developing and testing the prototypes of wind turbines and only 9% has been used in the wind turbines connected to the national electric grid thus far. The remaining 11% was exported in the form of manufactured wind turbines. The second largest import category is the miscellaneous category, which alone is responsible for 23% of total neodymium import in the form of NdFeB magnet alloy. However, nearly 61% of this imported magnet alloy is exported to the rest of the world mainly in the form of finished products, such as circulator pumps. The amount of neodymium imported in the form of NdFeB magnets contained in final products makes 90 Mg (32% of the total imported neodymium), out of which passenger vehicle and the home appliance categories have the largest share, with 48% each. The remaining 4% of the magnets contained in end-use products are imported in the form of IT applications (2%) and MRI machines (2%). Our estimates show that the in-use stock of neodymium in NdFeB magnets is 1424 Mg in 2012. Out of this, 38% of the inuse stock is contained in the wind turbine category, 28% is contained in home appliances, 18% is contained in passenger vehicles, 14% is contained in the miscellaneous category, and almost 2% is contained in MRI machines, IT applications, and 12233



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Figure 2. MFA of dysprosium contained in NdFeB magnets (Mg year−1) for Denmark in 2012, where the process boxes show the in-use stock + Δ stock for the specific product category. dStock, Δ Stock; EoL, end-of-life; IT, information technology; DVD, digital video disc; and MRI, magnetic resonance imaging.

mainly because of the long lifetime of key products, such as wind turbines (25 years), vehicles (16 years), and home appliances (up to 12 years). However, no neodymium was recovered from these end-of-life products in 2012 because of the diverse nature of products having these magnets as well as non-availability of commercial-scale technology to recover these resources in an economically feasible manner. Thus, in the current Danish waste management system, these critical

personal care products. In 2012, the amount of neodymium leaving the system was 56 Mg, mainly comprising of export of magnets and products in miscellaneous category (70%) and wind turbines (25%) as well as end-of-life products (5%). The overall amount of neodymium present in waste flows in 2012 was nearly 3 Mg, which mainly consisted of IT applications having 1.9 Mg, followed by MRI machines having 1.1 Mg. It can be noted that the amount of neodymium present in waste flows is quite low compared to what enters the system. This is 12234



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Figure 3. Comparative illustration regarding the share of different end-use sectors for the stock and flow model of neodymium contained in NdFeB magnets from 2012 to 2035.

Figure 4. Comparative illustration regarding the share of different end-use sectors for the stock and flow model of dysprosium contained in NdFeB magnets from 2012 to 2035.

resources presumably end up being impurities in the output material streams of an electronic waste pre-processing facility. Figure 2 shows the MFA results for dysprosium in 2012, where it becomes apparent that a total of 17.34 ± 2.14 Mg of dysprosium was imported in Denmark in the form of NdFeB magnets, equivalent to almost 1% of the global mine production of dysprosium in 2010. Similar to Nd MFA presented in Figure 1, the largest share of this import arises from the wind turbine category with 51%, followed by the home appliance category with nearly 17%. The third largest category is passenger vehicles with 16% share in total dysprosium imports to Denmark, followed by the miscellaneous category with almost 13% share. The remaining 3% of dysprosium imports fall into the categories of IT applications, personal care products, and MRI machines. The total in-use stock of dysprosium in Denmark is equivalent to 97 Mg, where the wind turbine category is again the major category with the share of 38%, followed by the home appliance and passenger vehicle categories with shares of 28.7 and 18%, respectively. The rest of the in-use stock (15.3%) comprises of the miscellaneous product category (13%), MRI machines (1.5%), IT applications (0.8%), and personal care products. In 2012, almost 1.95 Mg of dysprosium left the system mainly in the form of export of different end-use products (90%) as well as end-of-life products (10%). A total of 0.21 Mg of

dysprosium appeared in the waste stream, which mainly comprised IT applications (0.13 Mg), followed by MRI machines (0.08 Mg). However, there was no recovery of this dysprosium from the waste stream for the same reasons as explained above for neodymium. MFA of NdFeB Magnets in Denmark, 2012−2035. Apart from doing the MFA of NdFeB magnets in Denmark in 2012, we estimated the potential stocks and flows of these magnets in the future until 2035 as well. The main purpose of doing this was to enhance our knowledge on the future demand of NdFeB magnets as well as the resulting waste flows. Extending our MFA model by 2035 allows us to visualize the secondary supply potential of neodymium and dysprosium from major end-use products having long lifetimes, such as wind turbines and passenger vehicles. Figures 3 and 4 show the development regarding the imports, change in stocks, exports, and waste flows for neodymium and dysprosium, respectively, from 2012 to 2035 (see Figures S25−S28 of the Supporting Information for the detailed MFA results of neodymium and dysprosium for each year from 2012 to 2035 as well as the comprehensive results for each element in 2035). Results presented in Figure 3 reveal that the forecasted import of neodymium contained in the NdFeB magnets reaches 943 ± 135 Mg by 2035, which is approximately 3 times higher compared to the 2012 imports. The major growth can 12235



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vehicles, home appliances, and wind turbines. This offers better opportunities for efficient recovery of neodymium and dysprosium from the end-of-life products in the future. The reliable and consistent data to estimate the NdFeB magnet weight and its composition for a wide array of products is limited. In this study, we have provided primary data for NdFeB magnets and their composition for a majority of products in IT and personal care product categories. Furthermore, we supplemented our MFA model with secondary data regarding NdFeB magnet weight and composition in the remaining product categories, obtained from various sources, including the magnet and end-use product manufacturers. The comprehensive uncertainty analysis presented in this study provides a systematic overview of the level of input data uncertainty for both the weight and composition of the NdFeB magnets as well as the market share of products with these magnets within a single product type. These data can be applied to similar product types in other countries. In some cases, though, the data might not be representative for the similar products in developing countries depending upon the required functionalities of the products. For example, a conventional passenger vehicle in a developing country may not have the same amount of electric motors with NdFeB magnets for different automated features compared to the passenger vehicles in the developed countries. The overall MFA model results cannot be fully generalized, because Denmark offers a special case being the global leader of wind turbine technology. With regard to the projected developments for the MFA of NdFeB magnets in the future until 2035, we have preferred to present the conservative estimates in order not to overestimate the actual flows of NdFeB magnets. It is worthwhile to mention here that we have not incorporated any technological developments enforcing the increase and/or decrease and/or complete elimination of NdFeB magnet demand for various product categories (excluding the passenger vehicles) in our future estimates of the stock and flow model of NdFeB magnets in Denmark. This variable coupled with others, such as changing lifetime of products, future innovations, changing economic and social conditions, etc., have their own implications, which are beyond the scope of this contribution.

be visualized mainly from wind turbine and miscellaneous product categories, where import grows by a factor of 3.4 and 5.2, respectively, by 2035. The output flow (waste + export) of neodymium is 14 times higher in 2035 compared to 2012, primarily because of the expected big share of wind turbines and miscellaneous products being exported from Denmark in 2035. In 2012, export of wind turbines and miscellaneous products makes 95% (53 Mg) of the total output stream, where the remaining 5% is mainly comprised of end-of-life IT products as well as MRI machines. By 2035, export of wind turbines and the miscellaneous products is responsible for 77% (591 Mg) of the total output stream. The remaining 23% comprises end-of-life products arising from the miscellaneous product category, passenger vehicles, IT products, home appliances, MRI machines, and wind turbines. The overall amount of neodymium found in NdFeB magnets from the resulting waste stream is around 175 Mg in 2035 compared to only 3 Mg in 2012. Figure 4 shows the development of stocks and flows for dysprosium contained in the NdFeB magnets in Denmark from 2012 to 2035. It becomes evident that dysprosium import by 2035 is estimated to be 3 times higher compared to the import in 2012. This growth originates mainly from wind turbines, followed by the miscellaneous product and passenger vehicle categories. In contrast to the results presented in Figure 3 for neodymium, where the relative share of the miscellaneous product category reaches 36% for neodymium imports, it is interesting to note that this share seems to be only 19% of the dysprosium imports by 2035. This is mainly because of the low content of dysprosium in the magnets found in miscellaneous products, especially the circulator pumps. It can be seen that, in 2012, the maximum theoretical recovery potential of dysprosium is estimated to be only 0.2 Mg, whereas, in 2035, it is almost 11.4 Mg. This estimated high amount of dysprosium contained in NdFeB magnets found in Danish waste streams in 2035 comprises the end-of-life products originating mainly from the passenger vehicles (44%), followed by home appliances (34%), miscellaneous product category (16%), MRI machines (2.6%), IT applications (2.5%), wind turbines (0.7%), and personal care products (0.2%). The study has clearly shown that the current maximum theoretical recovery potential of neodymium and dysprosium from NdFeB magnets in Denmark in 2012 is only 3 and 0.2 Mg, respectively, which is equivalent to the amount of neodymium and dysprosium found in five 3 MW direct-drive wind turbines. Thus, it is undoubtedly more attractive and efficient to recover these resources from a major end-user, such as one wind turbine, compared to hundreds of thousands of computers and cell phones. As mentioned earlier, almost 60% of the current maximum theoretical recovery potential arises from only one category, IT applications. The major recovery challenge with this category is the diverse nature of end-of-life product types appearing in waste, coupled with the diversity of products even within a single product type. Moreover, the relatively low amounts of neodymium and dysprosium found in IT products render them relatively unattractive for recovery of these resources in an economically efficient manner. Notwithstanding the current small amount of neodymium and dysprosium found in waste streams and the challenges attached to its recovery, the estimated future amount of neodymium and dysprosium contained in NdFeB magnets found in waste stream seems to be higher mainly because of the appearance of major end-use products with long lifetimes, such as passenger

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ASSOCIATED CONTENT

S Supporting Information *

Additional methodological and experimental details, tables, and figures as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Telephone: +45-24409707. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge the TOPWASTE Project (www. topwaste.dk) and the REEgain Project (www.reegain.dk) for providing the opportunity to carry out this research and facilitating access to the necessary data. The authors are extremely thankful to Tom Ellegaard for giving the opportunity to collect and dismantle the electronic products with NdFeB magnets as well as to Lorie Hamelin and Marianne Wesnæs for their valuable comments. The authors are also grateful to Bjørn 12236



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Johansen, Peter Kjeldsteen, Poul Bøjsøe, Rune D. Grandal, and Aidan Cronin for necessary data provision. Assistance provided by David Laner throughout the modeling process is highly acknowledged.

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Material Flow Analysis of NdFeB Magnets for Denmark - American

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