Centennial Evolution of Aluminum In-Use Stocks on Our Aluminized

Article pubs.acs.org/est

Centennial Evolution of Aluminum In-Use Stocks on Our Aluminized Planet Gang Liu* and Daniel B. Müller Industrial Ecology Programme and Department of Hydraulic and Environmental Engineering, Norwegian University of Science and Technology, S.P. Andersens vei 5, 7491 Trondheim, Norway S Supporting Information *

ABSTRACT: A dynamic material flow model was developed to simulate the evolution of global aluminum stocks in geological reserve and anthropogenic reservoir from 1900 to 2010 on a country level. The contemporary global aluminum stock in use (0.6 Gt or 90 kg/capita) has reached about 10% of that in known bauxite reserves and represents an embodied energy amount that is equivalent to three-quarters of the present global annual electricity consumption. The largest proportions of in-use stock are located in the U.S. (28%), China (15%), Japan (7%), and Germany (6%) and in sectors of building and construction (40%) and transportation (27%). Industrialized countries have shown similar patterns of aluminum in-use stock growth: once the percapita stocks have reached a threshold level of 50 kg, they kept a near linear annual growth of 5−10 kg/capita; no clear signs of saturation can yet be observed. The present aluminum in-use stocks vary widely across countries: approximately 100−600 kg/capita in industrialized countries and below 100 kg/capita in developing countries. The growing global aluminum in-use stock has significant implications on future aluminum demand and provides important recycling opportunities that will be critical for greenhouse gas emissions mitigation in the aluminum industry in the coming decades.

1. INTRODUCTION Industrialization and urbanization are moving natural resources at a growing pace from the lithosphere into anthropogenic stocks of products in use.1−3 Understanding these in-use stocks has attracted growing interest in recent years because stocks (i) provide ultimate demand for services in our societies; (ii) generate a demand for upstream materials and release scrap at the end of product lifetime; and (iii) show more robust longterm historical patterns than flows and thus can help to better benchmark future scenarios. Dynamic material flow analysis (MFA) has been intensively applied to quantify material cycles and in-use stocks, offering new perspectives on a variety of topics, e.g., in what pattern and proportion materials are used4−6 and how stocks affect future material demand,7 recycling potential,8,9 and associated environmental impacts.10,11 Aluminum has been commercially produced only since the late 1880s when the Hall−Héroult process was discovered, but its use has grown rapidly since then, making it the second most used metal after iron. This growth has resulted in a notable shift of aluminum stocks from geogenic to anthropogenic reservoirs and in concerns for long-term availability of high-quality bauxite ores,12 as well as rising greenhouse gas (GHG) emissions.11 However, like other metals, aluminum can exist for a long time in products and infrastructures. A global estimate has shown that approximately 75% of all the aluminum ever produced is still in use.13 The growing inuse stocks may serve as future reserves for recycling and thus retain the value of the initial energy investments for primary production because recycling of obsolete products can reduce energy intensity by over 90% compared to primary production.14 © 2013 American Chemical Society

Previous studies have quantified aluminum in-use stocks using either a top-down approach based on estimation of annual consumption and product lifetime assumptions, or a bottom-up approach based on quantities of products in use and their aluminum concentrations. However, the quantity, quality, location, and historical patterns of global aluminum stocks are hitherto still poorly understood on a country level. First, because of the extensive amount of data required, these sparse studies have a small geographical coverage, mainly for the U.S.,10,15−17 Japan,18,19 China,18,20−22 and the globe as a total.23,24 Rauch25 has made a first estimate of aluminum in-use stocks for a complete country coverage, but these results are only for one year and remain subject to high uncertainty as they are approximated through linear regression of GDP and nighttime light satellite imagery data. Second, none of these studies have identified historical patterns of aluminum stocks in different countries, which would be critical to project future material demand (benchmark for future scenarios) and inform industry on recycling (capacity and location) and GHG emissions mitigation (strategy and effectiveness) efforts.10,11 In this paper, we develop a dynamic MFA model to quantify aluminum stocks and flows for all the countries from 1900 to 2010. We are essentially characterizing the centennial evolution of aluminum stocks to address two big questions: (i) After more than a century of growing demand and production, where Received: Revised: Accepted: Published: 4882

December 13, 2012 February 22, 2013 March 12, 2013 March 12, 2013 dx.doi.org/10.1021/es305108p | Environ. Sci. Technol. 2013, 47, 4882−4888

Environmental Science & Technology

Article

Figure 1. System definition and method for characterizing the anthropogenic metallurgical aluminum cycle. Transformation processes, market processes, and stocks and repositories are portrayed as boxes. Domestic and trade flows are portrayed as arrows. Colors of arrows indicate different determining approaches (legend in parentheses). Seven categories of final and obsolete products β (1−7) are: Building and Construction (B&C), Transportation (Trans), Containers and Packaging (C&P), Machinery and Equipment (M&E), Electrical Engineering (EE), Consumer Durables (CD), and Other Uses (Others).

is the aluminum currently in use (in which country, in what form, and how much) and how can it be recovered at the end of its products’ lives? (ii) What are the historical patterns of aluminum in-use stocks as societies evolve and how can these inform us about potential implications for future material demand, energy use, and GHG emissions?

Table 1. Mean Value Assumptions (τ) of Lifetime by Product Category and by Regiona region/product category (β) Europe North America Developed Asia and Oceania China rest of the world

2. MATERIALS AND METHODS The historical aluminum cycle and stocks in use were simulated using a system definition described in Figure 1. All processes comply with the mass balance principle and all stocks and flows were calculated in aluminum metallic equivalent. The model covers eventually all countries around the globe, which are grouped into 10 regions as shown in Figure S1 in the Supporting Information (SI). To keep the longest historical data, countries that have changed their territories or names were tracked back to their older names (e.g., “frm. USSR”). A production-driven top-down approach5,10 was used to determine historical aluminum in-use stocks (S(t)) as shown in eq 1. Starting points were either domestic shipment data of aluminum semiproducts wherever reported (method [1] in Figure 1; nineteen countries, SI Tables S1 and S2) or primary and recycled aluminum production statistics (method [2] in Figure 1; SI Table S3, all other countries). These shipment or production statistics were then adjusted by indirect trade of aluminum in semis and final products for calculating “aluminum flow entering use” (XM7−P8 in eq 1; flow from process M7 to process P8 in Figure 1). Historical trade statistics for about 130 aluminum-containing products were taken primarily from United Nations Comtrade Database,26 and then reviewed using a systems approach to identify and resolve the physical data gaps and inconsistences as detailed in SI Figure S3. Product lifetimes with normal distributions were assumed and differentiated by product category and by world region (Table 1; detailed in SI nTable S7). L (t, t′; τ, σ) is the probability that a product that entered at time t′ exists in use at time t, where τ and σ represent mean value and standard deviation, respectively. t

S(t ) =

trans

C&P

M&E

EE

CD

others

50 75 40

13 20 10

1 1 1

15 30 20

20 20 20

8 12 10

10 10 10

40 50

15 15

1 1

20 20

20 20

12 12

10 10

a

Normal distributions are applied, and standard deviations (σ) are set as 30% of the mean values (τ). Product categories (β) are spelled out in the caption of Figure 1.

Seven product categories (β, Figure 1) were used to estimate historical aluminum use in different applications. Historical statistics of the sector split from 1900 to 2010 were compiled and followed for the nineteen countries that use method [1], while a historical world average was applied to all other countries (SI Figure S2). Semimanufacturing (P5) and manufacturing (P7) processes yield new (preconsumer) scrap which is recycled either internally in the same plant (P6) or externally through the scrap market (P4). All yield ratios and losses along the life cycle (e.g., mining residue, red mud, and new scrap) were counted using transfer coefficients from industry statistics and estimates.10,24 The waste management and recycling process was balanced by the simulated flows leaving use and the simulated domestic scrap consumption. The overall data volume of the model is considerable: in total, some 50 000 production, consumption, and coefficient data points, and over 20 million trade data points were compiled. Wherever possible, historical data from 1900 to 2010 were used; when this was not feasible, figures from surrounding years were used and interpolated where possible. Sensitivity and uncertainty analyses were conducted to estimate the consequent impacts of parameter variations. For example, a Monte Carlo simulation was applied for the uncertainty of estimation of aluminum concentrations in commodities, which were derived from an intensive literature review (SI Table S6). Sensitivity of aluminum in-use stocks relative to trade data estimation was explored by using reported import data, reported export data, and the mean values of the two (which are used in subsequent analysis). The

7

∑ ∑ XM7 − P8, β(t )*(1 − ∑ L(t − t′, τβ , σβ)) t = 1900 β = 1

B&C

t ′≤ t

(1) 4883

dx.doi.org/10.1021/es305108p | Environ. Sci. Technol. 2013, 47, 4882−4888


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Figure 2. Density-equalizing maps of the aluminum stocks in 2010 in bauxite reserves (top) and in use (bottom). Country sizes are distorted in proportion to their absolute aluminum stocks. Color scale indicates per-capita aluminum stocks.

Table 2. Previous Estimates of Aluminum In-Use Stocks Compared with This Studya country U.S.

China

Japan South Korea Europe a

year

stock (Mt or Tg)

2009 2007 2006 2003 2002 2000 2009 2009 2005 2003 2003 2000 2007 2004 2003

151 (−7%) 91.1−97.6 (−73%) 146 (−5%) 120 (−13%) 142 (7%)

per-capita stock (kg) 490 (−8%) 490 (−5%) 410 (−13%) 360−400 (−21%)

88.9 (12%) 78.4 (1%) 48.8 (4%) 32 (−12%) 32 (−17%) 34.8 (−4%) 0.29 (−43%) 120−140 (29%) 72 (−30%)

57.7 (1%) 37.3 (4%) 25 (−12%) 250 (−17%)

160 (−12%)

method

reference

top-down top-down top-down top-down top-down bottom-up top-down top-down bottom-up top-down top-down top-down top-down top-down top-down

Chen and Graedel17 McMillan et al.15 Liu et al.10 Hatayama et al.18 Sullivan16 Recalde et al.27 Yue et al.22 Chen and Shi20 Wang and Graedel21 Hatayama et al.18 Hatayama et al.18 Murakami19 Jang et al.28 EAA/OEA29 Hatayama et al.18

Percentage in brackets indicates the maximum difference of result from previous studies with that for the same year from this study.

economically extracted, 6 Gt or 900 kg/capita) in 2010. Comparing to primary resources underground, secondary deposits of in-use stocks are more spatially distributed and of higher quality. The largest aluminum reserves are found in the southern hemisphere, over half being located in Guinea (0.16 Gt), Australia (0.12 Gt), and Brazil (0.07 Gt). This relates largely to the geological and climatic conditions that the formation of lateritic bauxite requires. The majority of aluminum in-use stocks, in contrast, are found in the northern hemisphere, predominately in North America, Western Europe, and Eastern Asia. This largely represents the uneven economic development25 and the consequent aluminum use in products and infrastructures around the globe.

aggregated uncertainties of all parameter variations were calculated using a Gaussian expansion method. Further details and data sources of production, trade, aluminum concentrations, yield losses, and product lifetimes are elaborated in the Supporting Information.

3. RESULTS 3.1. Present Aluminum Stocks in Use and in Bauxite Reserves. Figure 2 demonstrates that after more than a century of extraction and use, the global aluminum stock in use (0.6 Gt or 90 kg/capita; 1 Gt = 1Pg) has reached about 10% of currently known bauxite reserves (resources that can be 4884



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tend to have a higher share of aluminum stocks in Electrical Engineering (EE, about 50% for India), probably due to the cost and weight advantages of aluminum over copper and its consequent increasing use in transmission and distribution facilities,31 while industrialized countries, having already reached an advanced stage of infrastructural development, tend to have a higher share of aluminum stocks in Trans (especially in the U.S., Canada, Germany, and France) and B&C (especially in The Netherlands, Japan, and Italy). These patterns have significant implications on the quality and accessibility of postconsumer aluminum scrap; for example, it is easier to collect end-of-life vehicles than obsolete cables. 3.2. Historical Patterns of Aluminum Stock Growth. Aluminum in-use stocks show an increasing trend in almost all countries (Figure 4) and the 10 world regions (SI Figure S6) during the past century. The historical aluminum stock patterns of industrialized countries reveal some remarkable similarities: first a negligible level at the beginning of the 20th century followed by a relatively slow growth in the next few decades, then after reaching a threshold level of approximately 50 kg/capita, a near linear annual growth of 5−10 kg/capita up to recently. Although the growth rate of stocks appears to slow down after 2008 in a few industrialized countries (e.g., U.S., Japan, and Spain), it is not clear yet if this reflects first signs of a prolonged flattening, an effect of the recent economic crisis, or consequences of inaccurate recent trade data which are often revised in subsequent years. China and Brazil have just reached the 50 kg/capita threshold and are witnessing a sharp increase of in-use stocks. Russia also shows a resurgence and upturn of aluminum stocks after a decline during the post-1990s transition period. India and the other “Next Eleven” countries (except Mexico and South Korea), on the contrary, have still a relatively slow growth and a level below 40 kg/capita. Figure 5 shows that aluminum in-use stocks start to take off at percapita GDPs of 8000−10 000 dollars (PPP, 1990 international $), when a country has already industrialized. This threshold comes much later than that of iron stocks, where growth starts already at per-capita GDPs of 1000−4800 dollars.5 Then historical data depict that aluminum stocks increased to about 100−600 kg/cap when the GDPs increased to a level of 20 000−35 000 dollars/cap. It is interesting to observe that achieving the same per-capita economic outputs requires different levels of aluminum stocks among industrialized countries (e.g., less for U.K. and France than U.S. and Netherlands). Although the drivers behind this need more bottom up analysis, we speculate that this variation may reflect the flexible role of aluminum application in postindustrial societies and different socio-cultural and spatial patterns of cities in these countries (e.g., per-capita car ownership may be lower in denser cities33) and aluminum intensities in products (e.g., aluminum concentration in cars). Although aluminum is the third most abundant element (8%) in the Earth crust, bauxite is hitherto the principle ore to produce aluminum. The global aluminum stock in known bauxite reserves experienced a 10-fold growth since the 1950s and then gradually plateaued after the 1980s (Figure 6). The booming use of aluminum in vehicles and buildings after World War II has moved a considerable amount of aluminum from the lithosphere to the anthroposphere, with the share of anthropogenic aluminum stocks in the known overall stock constantly increasing from negligible in 1900 to 15% in 2010. Products in use and in landfills and obsolete products have dominated the anthropogenic aluminum stocks (55% and 20%, respectively, in 2010), indicating the magnitude of potential

On a per-capita basis, the present aluminum stocks in use vary significantly across different countries. Almost all developing countries and emerging economies have a level lower than 100 kg/capita (in comparison, the world average is about 90 kg/capita). Aluminum stocks in industrialized countries fall in a considerable range: roughly 100−200 kg/capita for Portugal, Spain, Sweden, Greece, Saudi Arabia, Mexico, and South Korea; roughly 200−400 kg/capita for Australia, Qatar, Belgium, Japan, Czech Republic, New Zealand, Italy, Ireland, France, Hungary, Denmark, U.K., and Finland; and roughly 400−600 kg/capita for the U.S., Canada, Netherlands, Switzerland, Germany, and Austria. A few countries have stocks higher than 600 kg/capita, which are either small rich countries (i.e., Singapore and United Arab Emirates) or primary aluminum producing countries (i.e., Bahrain, Iceland, and Norway; this may be due to inaccurate unwrought aluminum trade data and exclusion of industry inventory). The values found for aluminum stocks are generally in line with results of previous case studies. In most cases the difference is within a range of 30% (Table 2). In most cases our values are higher than previous estimates for the U.S., Japan, and South Korea and lower than previous estimates for China. Among other factors (e.g., lifetime and sector split), this may be largely explained by the explicit consideration of aluminum indirect trade in this study: Previous studies may have underestimated the net import of aluminum in semis and final products for industrialized countries and the net export of aluminum in semis and final products for emerging economics. We have listed aluminum stocks for all countries for the year 2000, 2005, and 2010 in SI Table S9. The year 2000 values for most of the countries appear lower than those from Rauch.25 This indicates that a nighttime light and GDP regression model may have overestimated the in-use stocks, as similarly found from another case study for copper.30 Figure 3 shows the varying composition of aluminum stocks for the 15 largest countries for stocks (over 80% of the global

Figure 3. Decomposition of aluminum stocks for the 15 largest countries for stocks. The countries from left to right are in descending order based on the year 2010 per capita stock. The gray line indicates the total stocks in Mt (the right y axis) in industrialized countries (names in black) and developing countries (names in blue).

total; with the U.S., China, Germany, and Japan appearing at the top). The majority of aluminum stocks reside in building and construction (B&C) and transportation (Trans) sectors in almost all countries (40% and 27%, respectively, on a global level). However, developing countries and emerging economies 4885



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Figure 4. Historical patterns of per-capita aluminum stocks in selected OECD countries, the BRICs (Brazil, Russia, India, China), and the Next-11 (1950−2010). The “Next-11” are the eleven countries identified by Goldman Sachs investment bank32 as having a high potential of becoming, along with the BRICs that they coined in 2003, the world’s largest economies in the 21st century based on macroeconomic stability, political maturity, openness of trade and investment policies, and the quality of education.

Figure 5. Per-capita aluminum stocks in use relative to per-capita GDP PPP for selected countries. The GDP data are measured based on purchasing power parity (PPP) in 1990 international Geary−Khamis dollars.34 The stock data are shown only until 2008 because of GDP data availability.

Figure 6. Historical global aluminum stocks in principal repositories, 1900−2100. Historical aluminum stocks in the lithosphere (S1 in Figure 1) include only known bauxite reserves36,37 (The present global reserve base is about 40% higher than global reserve); Bauxite residue storage include bauxite mining residue (S2) and red mud (S4); Slag repositories include spent potline (S5), salt slag (S6), and dissipative use (S8).

future scrap availability. The increasing bauxite residue storage and slag repositories cause not only potential loss of metallic aluminum (20% and 5% of the anthropogenic aluminum stocks, respectively, in 2010), but also growing environmental concerns and ecological risks (e.g., the red mud deposited in impoundments surrounding a refinery).35 3.3. Uncertainties of the Stock Estimation. The simulated stock results are mainly sensitive to product lifetime assumption and trade estimation, followed by domestic shipment to fabrication data and fabrication scrap generation ratio. The results are shown in Figure 7 for the case of U.S. and in SI Figure S6 for all the world regions. Aluminum concentration data from literature review may have high uncertainty for individual products, but a Monte Carlo simulation has shown that the aggregate uncertainty is low: a less than 20% difference for the maximum and minimum from the mean for the 2006 net import of U.S. aluminum indirect trade.10 In general, our estimation for historical aluminum stocks appears relatively robust. The aggregated uncertainties of historical aluminum in-use stocks induced by different parameter estimation are within a range of 20%.

4. DISCUSSION This study presents, to our own knowledge, the first global data set for aluminum in-use stock with country detail for the past century. The observed patterns of historical per-capita aluminum in-use stocks reveal a robust near linear growth trend in almost all industrialized countries after reaching a threshold level of 50 kg/capita. Although a few countries do show a flattening of stocks after 2008, no clear signs of saturation can be observed yet. These patterns lead to a hypothesis: that aluminum stocks are negligible in rural societies, then start to penetrate during industrialization, and take off and continue growing in postindustrial societies. This differs from iron, where saturation of per-capita in-use stocks has been observed for several industrialized countries since the 1980s.1,5 The difference may be explained by different roles of materials in societies. While iron is the most fundamental metal in industrial societies’ physical backbone, aluminum has a shorter use history and is mainly penetrating in automotive light-weighting (to reduce fuel consumption and GHG emissions in transportation), building, and other flexible applications. However, it is unlikely that 4886



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Figure 7. Sensitivity of the historical U.S. per-capita aluminum stock to different system parameters (left) and sensitivity of the 2006 net import of U.S. aluminum indirect trade to estimation of aluminum concentrations in products (right; 1000 times Monte Carlo iterations). The impacts of changes in unwrought aluminum production and forming scrap are hidden underneath the baseline. The aggregated uncertainties of historical stocks are indicated by the high and low bounds in gray lines.

such growth speed will continue indefinitely. More likely is that growth will eventually slow down, level off, or even decline over the long-term as services provided by aluminum products may become saturated (e.g., saturation of passenger car ownership) or as less aluminum is used to provide certain services (e.g., material substitution by composites in aircrafts). The present levels of aluminum stocks vary widely across countries, with the industrialized countries 1−6 times higher than the world average. This wide range of aluminum stocks differs from observation for iron in-use stocks, where difference among industrialized countries is relatively small.5 Although a more conclusive explanation of this behavior is not possible without more product disaggregated data, it can be speculated that lifestyle and spatial patterns of cities of a country may play a role here. This variation indicates that growth of aluminum in-use stock may vary slightly as societies adapt to dynamic historical, cultural, social, economic, and natural conditions; thus observed historical in-use stock patterns may be less robust to serve as benchmarks for future projections than iron, where growth takes place during industrialization and the range of application is less flexible. A more refined understanding of the underlying drivers is needed for robust forecasting of future aluminum stocks and flows. On the other hand, it suggests the possibility to achieve the same or higher services with lower stocks in future, as a complementary “material efficiency” strategy38 for climate change mitigation of future societies. Over one-tenth of aluminum stocks have already been transformed from bauxite reserves into products in use during the past century. This transformation would be expected to continue in the coming decades considering particularly the industrialization and urbanization of developing countries (e.g., China and India). Providing today’s industrialized-country average level of services for aluminum (400 kg/capita) worldwide, for example, would require additional conversion of about one-third of the currently known bauxite reserve from the lithosphere into the anthroposphere. While the geophysical constraint seems not to be a problem for bauxite for the next couple of decades due to its relatively high abundance, the growing trend of stocks will have several other interconnected implications: • The energy use and cost and GHG emissions of producing aluminum from bauxite will increase due to growing production and limits to clean energy supply. • The growing mining production can result in degradation of bauxite ore grade, which consequently leads to

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significantly more energy consumption during refining. For example, the lower quality bauxite that has already been largely used in China shows 2−3 times higher energy intensity than the average of Bayer process.39 • The primary production capacity has started to shift to countries where more coal-based and emission-intensive electricity is used for smelting (e.g., China) due to rising regional demand, resulting in an increase of total emissions from the global aluminum industry. • Regional resource depletion and changing trade patterns and dependencies may cause growing demand for transportation of raw materials and risks of supply chain disruption (e.g., due to geopolitical, economic, or social limits). Anthropogenic aluminum stocks (e.g., products in use and in landfills) constitute among the “highest quality aluminum mines” in the world.1,40 Therefore growing inuse stocks imply not only increasing aluminum demand, but also increasing future opportunities for recycling and consequent potentials to reduce energy use and GHG emissions. The present global aluminum in-use stock (0.6 Gt) approximately equals to an embodied energy amount of 14 PWh, assuming a per-ton aluminum energy intensity for smelting of about 15.2 MWh41 and for other upstream processes of about 8.6 MWh,11 which is equivalent to three-quarters of the present global annual electricity consumption. Since recycling of postconsumer scrap requires over 90% less energy than primary production, the “harvesting” of this growing embodied energy in the coming decades when the products reach their end of life will be one of the most critical strategies for GHG emissions mitigation in the aluminum industry.

ASSOCIATED CONTENT

S Supporting Information *

Model details, data sources, and additional figures. This information is available free of charge via the Internet at http://pubs.acs.org/.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] and [email protected]; tel.: + 47 73595156; fax: +47 73591298. Notes

The authors declare no competing financial interest. 4887



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the rapid increase in China’s aluminum production. Resour., Conserv. Recycl. 2012, 65, 18−28. (21) Wang, J.; Graedel, T. Aluminum in-use stocks in China: A bottom-up study. J. Mater. Cycles Waste 2010, 12 (1), 66−82. (22) Yue, Q.; Wang, H.; Lu, Z. Quantitative estimation of social stock for metals Al and Cu in China. Trans. Nonferrous Met. Soc. China 2012, 22 (7), 1744−1752. (23) Bruggink, P. R.; Martchek, K. J. Worldwide recycled aluminum supply and environmental impact model, Light Metals. Presented at the 133th TMS (The Minerals, Metals, and Materials Society) Annual Meeting, Charlotte, North Carolina, 2004; Tabereaux, A. T., Ed.; Charlotte, NC, 2004; pp 907−911. (24) GARC, Global Aluminium Recycling Model; Global Aluminium Recycling Committee, International Aluminium Institute: London, 2011. (25) Rauch, J. N. Global mapping of Al, Cu, Fe, and Zn in-use stocks and in-ground resources. Proc. Natl. Acad. Sci., U. S. A. 2009, 106 (45), 18920−18925. (26) UN Comtrade, United Nations Commodity Trade Database, United Nations Statistical Division. 1962−2011. (27) Recalde, K.; Wang, J.; Graedel, T. E. Aluminium in-use stocks in the state of Connecticut. Resour., Conserv. Recycl. 2008, 52 (11), 1271− 1282. (28) Jang, E.; Hong, S.-J.; Jung, J.-S.; Lee, J.-Y.; Hur, T. Analysis of Aluminum flow and stock in Korea. Presented at Life Cycle Assessment IX “Toward the Global Life Cycle Economy”, Boston, MA, 2009. (29) Aluminium Recycling in Europe: The Road to High Quality Products; European Aluminium Association and Organization of European Aluminium Remelters and Refiners: Brussels, 2006. (30) Takahashi, K. I.; Terakado, R.; Nakamura, J.; Adachi, Y.; Elvidge, C. D.; Matsuno, Y. In-use stock analysis using satellite nighttime light observation data. Resour., Conserv. Recycl. 2010, 55 (2), 196−200. (31) Radhakrishnan, P.; Kalra, G. Aluminium Industry in India: Problems and Prospects; National Council of Applied Economic Research, 1987; Vol. 1. (32) BRICS and Beyond; Goldman Sachs Global Economics Group, 2007. (33) Newman, P. Reducing automobile dependence. Environ. Urban. 1996, 8 (1), 67−92. (34) Maddison, A. Historical Statistics of the World Economy: 1− 2008 AD. Faculty of Economics, University of Groningen Groningen, Netherlands, 2010. (35) Review of Current Bauxite Residue Management, Disposal, and Storage: Practices, Engineering, and Science; CSIRO Minerals: Karawara, Australia, 2009. (36) Lyew-Allee, P. Bauxite reserves for the world aluminium industry: Perspects to the year 2020. In The 8th International Congress of the International Committee for Study of Bauxite, Alumina & Aluminium (ICSOBA) - “Energy and Environment in the Aluminium Industry”; The International Committee for Study of Bauxite, Alumina & Aluminium (ICSOBA): Milan, Italy, 1997. (37) Minerals Yearbook: Bauxite and Alumina and Minerals Yearbook: Aluminium; United States Geological Survey: Washington, DC, 1932− 2011. (38) Allwood, J. M.; Ashby, M. F.; Gutowski, T. G.; Worrell, E. Material efficiency: A white paper. Resour., Conserv. Recycl. 2011, 55 (3), 362−381. (39) Liu, L.; Aye, L.; Lu, Z.; Zhang, P. Analysis of the overall energy intensity of alumina refinery process using unit process energy intensity and product ratio method. Energy 2006, 31 (8−9), 1167− 1176. (40) Das, S. Achieving Carbon Neutrality in the Global Aluminum Industry. JOM, J. Min., Met. Mater. Soc. 2012, 64 (2), 285−290. (41) Global Aluminium Industry Sustainability Scorecard 2009; International Aluminium Institute: London, 2010.

ACKNOWLEDGMENTS We gratefully acknowledge Yan Wei, Lars Fabriciu, Colton Bangs, and Elodie Gourg for assistance on data collection; Stefan Pauliuk for discussion on trade analysis and support with MATLAB programming; Teresa Brown from British Geological Survey, E. Lee Bray from the U.S. Geological Survey, and George Banvolgyi from Bán-Völgy Limited Partnership for providing part of the data and useful clarification; and Georg Rombach from Norsk Hydro and Chris Bayliss from the International Aluminium Institute for thoughtful comments.

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Centennial Evolution of Aluminum In-Use Stocks on Our Aluminized

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