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2 Resources, Conservation and Recycling 54 (2010) Contents lists available at ScienceDirect Resources, Conservation and Recycling journal homepage: Substance flow analysis of aluminium in mainland China for 2001, 2004 and 2007: Exploring its initial sources, eventual sinks and the pathways linking them Chen Weiqiang, Shi Lei, Qian Yi Ministry of Environmental Protection Key Laboratory on Eco-industry, Department of Environmental Science and Engineering, Tsinghua University, Beijing , China article info abstract Article history: Received 12 July 2009 Received in revised form 15 October 2009 Accepted 21 October 2009 Keywords: Substance flow analysis Stocks and flows Aluminium consumption Aluminium recycling Aluminium trade Mainland China Based on the characterization of aluminium life cycle in the anthroposphere, stocks and flows accounting of aluminium in mainland China for 2001, 2004 and 2007 was performed in this paper. Findings include the following: (1) the production and consumption of aluminium contained in aluminium-containing products generated from each life process grew from 2001 to 2004, and then to 2007; (2) the share of recycled aluminium in both production and consumption of unwrought aluminium was in the range of 20 26%, and a majority of aluminium scrap used to produce recycled aluminium for 2004 and 2007 came from net import, which revealed that China was still in the stage of mainly depending on primary aluminium rather than secondary aluminium and the in-use stock of aluminium was still too small to generate enough end-of-life (EOL) scrap; (3) China was a net importer of aluminium from the life cycle perspective, with total net import increasing from 2001 to 2004, and then to 2007; as for the trade structure, China was a net importer of raw materials including bauxite, alumina, EOL products and aluminium scrap, while a net exporter of unwrought aluminium and final products, and changed from a net importer of wrought products in 2001 and 2004 to a net exporter in 2007; (4) total quantity losses of aluminium in China increased from 2001 to 2004 and then to 2007 as a result of the growth of production; (5) depletion of domestic ore stock in China also increased from 2001 to 2004, and then to 2007, making China s depletion time of bauxite probably less than 15 years; (6) growth of in-use stock was 2.4 kg per capita, 3.7 kg per capita and 6.3 kg per capita for 2001, 2004 and 2007, respectively; (7) more than 80% of the addition of aluminium to the deposited stock came from aluminium losses in Bauxite Mining and Alumina Refining processes Elsevier B.V. All rights reserved. 1. Introduction Aluminium is the third most abundant element after oxygen and silicon, accounting for 8% of the earth s crust (Sverdlin, 2003). As a result of the combination of various excellent properties such as light weight, high strength, good malleability, excellent thermal conduction and high corrosion resistance, aluminium is recognized for its versatility and is used more than any other metal except steel. However, production of primary aluminium, to some extent as well as secondary aluminium is highly energy intensive and with heavy environmental burdens associated with resources extraction and pollutant emissions. As illustrated in Fig. 1, the production of alumina and primary aluminium increased very quickly after 2000 in mainland China, with their respective shares of global production rising from 9.0% and 13.2% in 2000 to 37.7% and 51.1% in This rapid growth of aluminium production, to large extent, resulted in the increases and structure changes of trade of aluminium-containing products 1 (ACPs) for China (see Section 5.2). What is more, it inevitably brought about great challenges to China resource and environment, mainly in the aspects of (1) lack of raw materials such as bauxite, energy and aluminium scrap, and (2) the environmental burden associated with the extraction of bauxite, as well as the emissions of red mud, fluoride and greenhouse gas during production. Therefore, it is necessary to study the anthropogenic aluminium cycles in China, especially to understand the change trends of aluminium production, consumption, trade, loss and recycling after Substance flow analysis (SFA), which invokes mass conservation to track the fate of metals and to evaluate the environmental burdens they carry with them as they move through their life cycles, has been applied to analyze the aluminium cycles in the anthroposphere. The existed literatures applying SFA (or like SFA) method which can be found by authors are summarized in Table 1. Among Corresponding author. Tel.: ; fax: address: slone@tsinghua.edu.cn (L. Shi). 1 Aluminium-containing products in this study refer to all products containing aluminium in its metal or chemical compound forms generated from its each life process, but not only the final products entering the Use stage /$ see front matter 2009 Elsevier B.V. All rights reserved. doi: /j.resconrec

3 558 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Table 1 A brief literature review on existing aluminum substance flow analysis. Spatial scale Temporal scale Brief introduction and/or comments Japan A dynamic model is applied to estimate the quantities of old scrap by both end-use and alloy (Hatayama et al., 2007). Japan 2003 Detailed and quantitative analysis of aluminium dross generation, recycling and disposal (Nakajima et al., 2007). Germany Excellent models are developed to estimate the potential arising of old scrap from discarded products by end-use (Melo, 1999). England One year static aluminium SFA for 2001 and multi-year dynamic SFA during are presented; value chain analysis is combined with SFA to estimate the resource productivity and efficiency. Import and export are detailed considered but losses are almost completely neglected (Dahlström et al., 2004; Dahlstrom and Ekins, 2007). Japan, USA, Europe and China Dynamic SFA and multi-material pinch analysis are integrated to estimate the in-use stock and the recycling potential of aluminium by both end-use and alloy (Hatayama et al., 2009). EU Excellent mass balance analysis in the aluminium recycling industry (Boin and Bertram, 2005). EU-27 and EFTA countries a 2005 Excellent mass balance analysis in the primary aluminium production, semi-production, and aluminium recycling industries (EAA, 2008). Global 2003, A comprehensive model b is developed to provide the first quantitative assessment of annual global aluminium and life cycle inventory flows. Losses are considered but not comprehensive and detailed enough (Martchek, 2006). a Norway, Switzerland, and Iceland. b Data of this model has been updated annually by International Aluminium Institute (IAI) and European Aluminium Association (EAA) at global and European level from 2003, respectively. them, one is at the global level (Martchek, 2006), two at the European Union level (Boin and Bertram, 2005; EAA, 2008), and the others at the national level (Melo, 1999; Dahlström et al., 2004; Dahlstrom and Ekins, 2007; Hatayama et al., 2007, 2009; Nakajima et al., 2007). Many of them developed or applied so-called dynamic models to estimate the long-term generation of old aluminium scrap by end-use (Melo, 1999; Dahlström et al., 2004; Hatayama et al., 2007, 2009). However, except Dahlström et al. (2004) and Martchek (2006), most of them focused only on one or some of the life processes, but not the whole life cycle of aluminium in the anthroposphere. Moreover, studies concentrating on aluminium SFA in China could not be found as yet. In the last several years, the stocks and flows (STAF) project, initiated by the Center for Industrial Ecology at Yale University, developed a comprehensive and generic SFA framework in which the anthropogenic metal life cycle for a system defined by certain temporal and spatial boundaries are characterized on its four life stages (Wang et al., 2007). Based on this framework, quantitative evaluations of 1 year static anthropogenic life cycles of copper and zinc for the year 1994 (Graedel et al., 2004, 2005), silver for the year 1997 (Johnson et al., 2005), as well as chromium, iron, nickel, and lead for the year 2000 (Johnson et al., 2006; Wang et al., 2007; Mao et al., 2008a,b; Reck et al., 2008), have been completed by Yale University at three levels, countries and territories level, nine world regions level, and the planet level. Moreover, the results of these studies revealed great implications for further studies on resource policy, industrial development, and waste and environmental management of metals. Therefore it is very important and applicable for the STAF framework to be used to study the anthropogenic aluminium life cycle in China. Considering the great expansion of aluminium production after 2000 in China, this paper is dedicated to examining the changes of flows and stocks accumulations or depletions in China in this period. For this purpose, generally it would be better to apply the dynamic SFA method. However, dynamic models would require multi-year data which are difficult to acquire for China, especially data on long-term aluminium consumption by end-use and the lifetime distribution of each end-use. Therefore, we selected three typical years, 2001, 2004 and 2007, and then examined the growth and structural changes of flows and stocks changes in these 3 years, to roughly observe the change trends of aluminium stocks and flows after This paper is organized as follows: the next section qualitatively describes the aluminium life cycle in the anthroposphere; Section 3 defines the scope and system boundaries of this study and details the accounting methodology used for it; Section 4 is dedicated to a detailed description of data collection; Section 5 presents our results; finally the paper ends by discussing the conclusions that can be drawn. 2. Background: life cycle of aluminium in the anthroposphere Fig. 1. China s production rates of alumina and primary aluminium and China s share of world production between 2000 and Production rates of alumina are measured in Gg (thousand metric tons) alumina per annum, while production rates of primary aluminium are measured in Gg Al per annum. Data sources: IAI (2008). According to the STAF framework, the life cycle of aluminium in the anthroposphere is composed of four principal life stages as shown in Fig. 2: production (P), fabrication and manufacturing (F&M), Use (U), and waste management and recycling (WM&R). Except for Use, each of these life stages is divided into several substages which are depicted as the solid line rectangles in Fig. 2 and described in Table 2. In this paper, both the four principal life stages and their sub-stages are also referred to as life processes. Every life process produces ACPs as specified in Table 3 and results in quantity losses of aluminium as described in Table 4. Aluminium is produced from ore (for primary aluminium) or scrap (for secondary aluminium) in the modern world. The production chain of primary aluminium can be expressed as some sub-stages of production stage: (1) mining of bauxite and other

4 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Fig. 2. Schematic diagram for an anthropogenic aluminum life cycle. NM = non-metallic use; IG stock = industrial and governmental stock; L = dissipated losses to environment. Refer to Table 2 for the symbols of the life processes. Table 2 Symbols and indices of life processes of anthropogenic aluminium cycle in this study. Life processes Symbols Indices Production P Bauxite mining BM 1 Alumina refining AR 2 Primary aluminium smelting PAS 3 Ingot casting IC 4 Fabrication and manufacturing F&M Foundry casting FC 5-a Fabrication of wrought products FW Rolling RO 5-b Extrusions EX 5-c Other fabrication processes OT 5-d Manufacturing MAU 6 Use U Use U 7 Waste management and recycling WM&R Collection of EOL products and scrap CES 8 Treatment of scrap TS 9 Melting of scrap MS 10 ores; (2) processing of bauxite and preparation of alumina; (3) electrolysis of alumina to smelt molten primary aluminium, and (4) casting of molten aluminium to produce a variety of ingots, including ingot for remelting, ingot for rolling (slabs), ingot for extrusion (billets), wire bar ingot, and to a lesser extent, ingot for forging. In some cases, due to proximity, molten aluminium is also trucked directly to a nearby foundry to produce castings. Aluminium enters final product in three different types, mainly in aluminium alloys, with most of the remainder in commercialpurity aluminum and a small quantity in super-purity aluminum. Aluminium alloys are divided into wrought alloys and casting alloys 2 which are used for producing wrought products and castings, 3 respectively. Wrought products generally comprise (1) rolled products such as plate, sheet, strip and foil, (2) extruded products such as section, rod, bar, tube and wire, and (3) forgings, as well as other fabricated products. As for aluminium foundry casting, there are three main processes: sand casting, permanent mold casting, and die casting, which usually produce a finished part in one step. Wrought products and castings from the primary or secondary route have to be further processed in the downstream supply chain in order to be used in making final products (Dahlström et al., 2004). Because final products containing aluminium are so numerous and diverse that it is difficult to categorize them distinctly, the aluminium flows thus become highly complex and statistics are sparse at the manufacturing stage. U.S. Geological Survey (USGS, 2006) classifies aluminium final products into seven categories as listed in Table 3, with each of them including many sub-categories and each sub-category comprising a great number of final products. There are two characteristics which make the Use stage different from the other processes. First, the material transformations of this stage are usually unintentional and an effect of products use (Dahlström et al., 2004). There are three types of transformations, (1) corrosion, (2) dissipation, and (3) contamination in this stage, which usually result in the quantity and quality losses of aluminium that should not be neglected in the SFA research. Second, because most of the final products may serve in the Use stage for a long time and will not be consumed, an in-use stock of aluminium will gradually form and enlarge in a defined geographical area such as a city or a country. Both discarded final products which reach their end-of-life (EOL) and the new aluminium scrap are processed in the WM&R stage. The recovered portion of discarded products which are collected and treated for recycling is designated as old scrap (or obsolete scrap or post-consumer scrap). New scrap is generated during the production and F&M stages up to the point where the products are sold to the final users. Both old and new scrap 2 Casting alloy is also referred to as cast alloy. 3 Wrought products are usually referred to as semi-fabricated products, semifabrications, semi-finished products, or semis. Castings can also be considered as semi-finished products but as soon as they have been submitted to finishing/polishing operations they are more considered as finished products (Leroy, 2008).

5 560 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Table 3 HS codes of ACPs generated from each life process and data sources of aluminium contents. Life processes ACPs HS codes Data sources of aluminium contents BM Bauxite , SECSPC (2004b) AR Alumina, aluminium hydroxide , SECSPC (2004b) PAS Molten primary aluminium a IC Primary aluminium ingot b , SECSPC (2004b) and Wang et al. (2004) FC Castings c RO Plate, sheet, strip, and foil 7606, 7607 SECSPC (2004a,b) and Wang et al. (2004) EX Section, rod, bar, tube, and wire 7604, 7605, 7608, 7609 OT Powders d 7603 MAU Transportation All commodities in Chapters SECSPC (2004a,b), Wang et al. (2004), USGS (2005), Lou and Shi (2008), Recalde et al. (2008), Wang (2008b) and Xiong (2008). Building and construction 7610, Machinery and equipment 7614, 7615, some products in Chapter 84 Electrical and electronic Part of commodities in Chapters 84 and 85 Consumer durables Part of commodities in Chapter 84 Containing and packaging e Others 7611, 7612, 7613, U EOL products f CES Scrap collected g 7602 SECSPC (2004a) TS Scrap treated MS Recycled aluminium SECSPC (2004b) and Wang et al. (2004) Refer to Table 2 for the symbols of the life processes. a Molten primary aluminium should be cast into ingot before marketed. b Customs statistics do not tell primary aluminium from recycled aluminium. In this study, we assumed that all of the unwrought not-alloyed aluminium, with its HS code , was primary aluminium; whereas 80% of unwrought aluminium alloys, with its HS code , were recycled aluminium, and the 20% remainder was also primary aluminium (Wang, 2008a). c Trade data special on aluminium foundry castings do not exist in customs statistics based on HS. Therefore, the import and export of castings should be regarded as part of that of final products, and could not be calculated separately. d Only powders in the HS, with its HS code 7603, could be obviously regarded as ACPs of OT process which may also include various other commodities. e Commodities that can be regarded as Containing and Packaging are very difficult to be determined. f Net import of aluminium embodied in EOL products were directly estimated according to expert interviews and literatures as mentioned in Section 4.1. g Customs statistics do not distinguish between new scrap and old scrap, as well as between treated scrap and not-treated scrap. In this study, we assumed that aluminium waste and scrap, of which the HS code was 7602, was totally not-treated old aluminium scrap. Table 4 Description and classification of aluminium quantity losses along its anthropogenic life cycle. Life processes Type of losses Description of aluminium quantity losses BM Deposited Part of bauxite is destroyed, discarded or left in or near the mine. BD a Deposited Tailings are deposited. Desilication only occurs in the newly developed ore-dressing Bayer process in mainland China. AR Deposited Alumina contained in red mud is deposited. Dissipated Dust of bauxite and alumina is dissipated. PAS Deposited Alumina or aluminium contained in the spent pot lining and carbon residue are landfilled. Dissipated Dust of alumina is dissipated. IC Dissipated A small portion of molten aluminium is oxidized during melting and casting. Deposited Part of dross is landfilled. FW Dissipated Small part of aluminium is oxidized because of internal scrap remelting. MAU Dissipated Aluminium may be lost in the surface treatment process. But the share of aluminium loss is very small and can be neglected. U Dissipated Dissipative uses of aluminium, mainly comprising deoxidation aluminium used in the steel industry and aluminium powder used for explosives, fertilizers, paints, etc. Dissipated Corrosion of aluminium. CES Deposited Not collected EOL products may hibernate in somewhere or be landfilled. TS Deposited and dissipated Aluminium lost during separation of aluminium from other materials may be landfilled or dissipated into the environment. MS Dissipated Small part of molten aluminium is oxidized during melting. Deposited Part of dross and salt slag are landfilled. Refer to Table 2 for the symbols of the life processes. a BD stands for the bauxite desilication process which only exists in the factories applying the ore-dressing Bayer process which firstly beneficiates the domestic diaspore bauxite to reduce the silicon content and then uses the Bayer process to refine alumina in China. Because the production from factories of this kind only accounted for few percentages of total alumina production in China, we do not calculate the loss of aluminium from this process here.

6 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Fig. 3. Schematic diagram of mass balance for each life process of aluminium life cycle. LP i : life process i. S i : Stock of ACPs generated from LP i. will enter the aluminium recycling chain which consists of three sub-stages (Boin and Bertram, 2005): (1) collection of discarded products and new scrap, (2) treatment or preparation of scrap, and (3) smelting or melting 4 of scrap. According to Gleich (2006), a sustainable metals industry is essentially based on a closed loop of metals, which is as far as possible free of quantity and quality losses, in the technosphere. Quantity losses of aluminium occur in every life process of aluminium life cycle, and are divided into two main kinds as listed in Table 4: (1) the deposited losses which are either landfilled or deposited in the residue/slag ponds, result in the form of deposited stock, and may be re-exploited in the future; (2) the dissipated losses which either lose their metal property or dissipate into the environment, result in the form of dissipated stock, and have no possibility to be reused or recycled. While quality loss of aluminium and its alloys generally occur during recycling and are very usual owing to the mix and contaminations of different materials and alloying elements. A typical case is that wrought alloys often do not enter the closed loop recycling chain but undergo downgrade utilization, being converted to casting alloys after recycled. 3. System boundaries and accounting method 3.1. Scope and system boundaries Spatial and temporal boundaries define the system analyzed in MFA/SFA (Spatari et al., 2002). The spatial system boundaries of this study are the geographical borders of mainland China. Because most data are available on annual basis, average annual magnitudes are taken for the years of 2001, 2004 and Following conventions in SFA, all stocks and flows values of this study refer to the mass of aluminium only in pure form excluding mixtures and alloying alloys. For bauxite and alumina where aluminium exists in its chemical compound form, the mass of aluminium is calculated according to the mass of aluminium included in the Al 2 O Classification of stocks and flows Accounting of stocks (usually changes of stocks) and flows is the central task in the SFA of metals. As depicted by Fig. 3, there are several flows associated with each life process. Except for the Use process, the total input to a life process should be equal to the total output from it as explained by the following equation: F input + Fimport = F output + F export + F loss (1) where i is the index for life processes as given in Table 2; j is the index for the three selected years, 2001, 2004 and 2007; F input is 4 According to (Boin and Bertram, 2005), scrap smelting and melting can be equally used for the process of extracting aluminium from aluminium scrap in refiners and remelters. the aluminium contained in the material demanded by life process i to produce its ACPs in year j; F import is the import of aluminium embodied in ACPs generated from life process i for year j; F export is the export of aluminium embodied in ACPs generated from life process i for year j; F loss is the quantity losses of aluminium from life process i in year j; and F output is the aluminium contained in ACPs generated from life process i and entering China s domestic market in year j. Associated with each life process, there is a temporary stock of ACPs generated from that process and stored in the industrial, commercial or governmental warehouse. An example and mostly concerned stock of this kind is the stock of unwrought aluminium, because it is very important to metal market and change of this stock usually greatly influence the short-term price fluctuation of aluminium. However, what should be concerned in the SFA study are the long-term stocks of aluminium which are crucial to the sustainability of its utilization but not the temporary stocks of ACPs. According to Kapur and Graedel (2006), long-term stocks of metals which could be calculated include (1) ore stock, (2) in-use stock, and (3) expended stock. Ore stock is the amount of a mineral resource existing now in concentrated form in natural deposits and is synonymous to the reserve base. In-use stock is the amount of a material taken from nature for human use and is still in active use now. Expended stock is the amount of a material that has been used for human purposes and then discarded or that has been lost from the technosphere. It comprises two components: (1) deposited stock which results from the deposited losses and (2) dissipated stock which results from the dissipated losses. Because of the form of inuse stock, the mass balance equation for the Use process should be expressed as follow: F input + Fimport + S inuse 1 = Foutput + F export + F loss + Sinuse (2) where S inuse is the in-use stock of aluminium by the end of year j in mainland China. Among the flows associated with each life process, as shown in Fig. 2, there are two kinds of flows, (1) the loss flows (F loss ) and (2) the trade flows (F import and F export ) which directly make the aluminium enter or leave China s anthroposphere. However, the effect of two other flows, F input and Foutput, is to make the aluminium go through China s anthroposphere along its life cycle. The relationship between F input, Foutput, and S, the temporary stock of aluminium contained in ACPs generated from life process i by the end of year j, could be expressed as Eq. (3): F output + S S 1 = F input (3) AL,i+1,j Considering the in-use stocks as the pivotal engine that drives the anthropogenic aluminium life cycle (Muller et al., 2006), as depicted in Fig. 2, we classified the F input and Foutput into two other kinds: (3) the feed-in flows to the in-use stock which originate from ore stock; (4) the recycling flows of aluminium scrap, mainly old scrap generating from in-use stock, as well as new scrap generating from production and F&M stages, both of which finally go back to the in-use stock. The purpose of distinguishing all the flows into these four kinds is to help expressing and understanding the results of aluminium SFA, and to find potential policy implications in the aspect of optimizing each kind of flows Accounting method of flows Two indices, production and consumption, are important to the calculation of flows and essential to express the results of aluminium SFA. Theoretically, P and AC, the production and

7 562 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) apparent consumption of aluminium contained in ACPs generated from life process i in year j, could be calculated by Eqs. (4) and (5), respectively: P = P p,i,j C i (4) AC = P + F import F export + S S 1 (5) where P p,i,j = the production of ACPs generated from life process i in year j; C i = the average aluminium content of ACPs generated from life process i. Except for the Use process, P could also be calculated as follow equation: P = F input Floss (6) Unfortunately, because data on changes of temporary stocks of all kinds of ACPs, even unwrought aluminium, were not documented in China, we assumed that no significant accumulation or depletion of stock occurred for 2001, 2004 and Thus, Eq. (5) simplified as follows: AC = P + F import F export = F output (7) Among all flows, only the trade flows can be calculated directly independent from other flows. F import and F export are calculated according to Eqs. (8) and (9), respectively: F import F export where F import p,i,j = F import C p,i,j i (8) = F export C p,i,j i (9) and F export was equal to the import and export of ACPs p,i,j generated from life process i for year j, respectively. With F import and F export, net import of aluminium embodied in ACPs generated from life process i, F netimport, can be calculated by the following equation: F netimport = F import F export (10) Theoretically, F loss, the quantity loss of aluminium from life process i (except for the Use process) in year j, could be calculated by the following equation: F loss = Finput Rloss (11) where R loss is the loss rate of aluminium from life process i in year j. For the Use process, only deoxidation aluminium used by steel industry was considered owing to data availability, the Eq. (11) was thus not applicable and F loss was estimated as follows: AL,7,j F loss AL,7,j = P steel,j D forsteel (12) where P steel,j = the production of steel in China for year j; D forsteel is the average consumption of deoxidation aluminium per ton steel. F T-netimport and F T-loss, which indicates Total Net Import and Total Losses of aluminium in year j from the life cycle perspective, respectively, could then be calculated by Eqs. (13) and (14): F T-netimport F T-loss = i = i F netimport (13) F loss (14) For every life process, besides the trade flows, it is generally to calculate P or F input first, and then use the mass balance Eqs. (1), (6) and (11) to calculate the loss flows, AC, and F output. For the processes of BM, AR, IC, and FW (including RO, EX, and OT), with data on P p,i,j collected from official statistics, P could be calculated by Eq. (4). For the processes of PAS, FC, MAU, CES, TS and MS, the F input were calculated according to the Eq. (3). For the Use process, it seems prevalent and most accurate to use dynamic models to estimate the generation of old scraps, especially when statistics does not exist. However as mentioned before, this method requires data on historical consumption by end-use and the lifetime distribution of each end-use which are both sparse in China. Therefore, we used a simplified dynamic model, that is, the fixed-lifetimes approach (Melo, 1999) to estimate the production of old scrap. As shown in Eq. (15), we assumed that the aluminium entering the Use stage 12 years ago, F input, subtracted by the amount of deoxidation aluminium used by the steel industry, F loss, was available AL,7,j 12 AL,7,j 12 to be collected as old scrap for the selected year j: P AL,7,j = F input AL,7,j 12 Floss AL,7,j 12 (15) As depicted by Fig. 5, it is important to point out that we assumed all the new scrap was recovered within the F&M stage and ignored to estimate its amount because of the following reasons: (1) unlike other metals such as copper, new scrap of aluminium generally does not go back to the production stage to be refined; (2) home scrap from FW and FC processes is generally recovered and remelted in the same factory where it is generated; (3) many fabricators, foundries and manufacturers construct their own remelters or send their prompt scrap directly to certain external remelters which finally return the recycled aluminium to them; (4) therefore we regard the F&M stage as a black-box without exchanges of new scrap with other life processes Calculation of stocks changes For the stocks considered in this study, what could be calculated are the changes of ore stock, in-use stock, deposited stock and dissipated stock, but not the stocks themselves. Ore stock of aluminium decreases year by year. Depletion of Ore Stock, S ore, could be calculated by the following equation: S ore = P AL,1,j + F loss AL,1,j (16) In-use stock of aluminium is increasing year by year in contemporary China. Therefore, Growth of In-use Stock, S inuse, could be estimated by the mass balance between the inflows into the Use stage and the outflows out of it: S inuse = F input AL,7,j P AL,7,j F loss AL,7,j (17) For calculating the changes of deposited stock, it was necessary to tell deposited losses from dissipated losses. However, both deposited losses and dissipated losses occur for many processes. We assumed that the quantity losses of aluminium from BM, AR, CES and TS were deposited losses while the quantity losses from other processes were dissipated losses. Therefore, Addition to Deposited Stock, S deposited, and Addition to Dissipated Stock, S dissipated, could be calculated according to Eqs. (18) and (19), respectively: S deposited S dissipated = F loss AL,1,j + Floss AL,2,j + Floss AL,8,j + Floss AL,9,j (18) = F T-loss S deposited (19)

8 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Table 5 Loss rates of aluminium in its different life processes. Life processes BM AR PAS IC FC FW U CES TS MS Units % % % % % % kg AL/t steel % % % a,b 10.4 b 1.7 b 0.8 c 5 d 4.7 b 1.8 e 20 f 5 e 7 g,h a,b 11.1 b 1.9 b 0.8 c 5 d 4.5 b 1.8 e 20 f 5 e 7 g,h b 16.2 b 2.1 b 0.8 c 5 d 4.8 b 1.8 e 20 f 5 e 7 g,h Refer to Table 2 for the symbols of the life processes. a MLR (2002). b CNMIA ( ). c Du (2007). d CMRA (2007). e EAA and OEA (2004). f Wang (2002). g Wang (2008b). h Li et al. (2006). 4. Data preparation and data quality 4.1. Data classification and collection According to the accounting method, data collected for this study could be grouped into four categories: (1) data on production of ACPs; (2) data on import and export of ACPs; (3) data on aluminium contents of ACPs; (4) data on loss rates or their corresponding indices in every life process. Data on production of bauxite, alumina, primary aluminium and wrought products after 1980 were well compiled annually by China Nonferrous Metals Industry Association (CNMIA, ) and therefore easily collected. However, data on generation of aluminium scrap, production of recycled aluminium and foundry castings, as well as consumption of aluminium by end-use were not available in official statistics and therefore should be calculated as described in Section 3.3 or be acquired from expert interviews (Wang, 2008b; Xiong, 2008). Data on import and export of ACPs classified according to Harmonized Commodity Description and Coding System (HS) 5 could be obtained from online database (UN, 2008). Traded commodities included in the customs statistics are listed in Table 3 according to their affiliation with different life processes. However, challenges exist in determining the inventory of aluminium final products. Besides those which were included in Chapter 76 of HS, we regarded all commodities in Chapters to be Transportation, selected more than 60 four-digit code commodities in Chapter 84 as Machinery and Equipment, about 10 four-digit code commodities in Chapter 84 as Consumer Durables, and about 20 four-digit commodities in Chapters 84 and 85 as Electrical and Electronic. For the EOL products of which the trade data are generally not contained in the present customs statistics, the import of embodied aluminium was prudently estimated according to expert interviews and literature (Wang, 2002, 2008b; Li, 2003; Xiong et al., 2005), whereas the export was considered to be zero. Data sources of aluminium contents are listed in Table 3. For bauxite, alumina, aluminium hydroxide, unwrought aluminium, aluminum semi-products, aluminium scrap and the final products included in Chapter 76, it is easy to estimate their average aluminium content according to standards on ACPs issued by the Chinese government and some literature. However, great challenges exist in determining the aluminium content of final products included in Chapters of HS. In this study, we estimated or inferred data on them with the help of literature and expert interviews, but we would like to point out that these data might be of high uncertainty. Data on loss rates of aluminium in its ten life processes for years 2001, 2004 and 2007 are summarized in Table 5. These data were calculated according to various corresponding indices (e.g. overall recovery rate of alumina for AR process, metal consumption per ton fabrication product for FW processes, and collection rate of old scrap for CES process) of which the values were acquired from official statistics, literature or expert interviews. However, data on the loss rates of aluminium in MAU process were not available, and we thus ignored to estimate losses in this process. For the Use stage, only deoxidation aluminium data used by the steel industry were estimated and aluminium consumption per ton steel was obtained from literature Data quality and data uncertainty The data useful for characterizing cycles of materials used in our anthropogenic society are highly variable in quality and level of detail. In their study on copper cycles, Graedel et al. (2002) pointed out that data on early life stages (mining, extraction, processing, fabrication) is relatively easy to acquire from public sources and of good quality, whereas data for MAU and Use stages is much 5 Trade commodities included in the China Customs Statistics Yearbook are classified based on the HS which is regularly reviewed and revised. HS-1996 contains 21 sections, 97 chapters and 1241 headings at the four-digit level, also it represented a total of 5113 separate categories of goods identified by a six-digit code. China adopts the adapted HS which have been added two digits to further classify products of particular national interest (8-digit level) (GAC, 2007). Because the China Customs Statistics data are submitted to the United Nations annually, it is convenient to acquire the data of six-digit categories of commodities from the online UN comtrade database (UN, 2008). Fig. 4. Number of types of ACPs and number of organizations processing, producing, or utilizing ACPs in different life processes of the anthropogenic aluminium cycle in contemporary China. Refer to Table 2 for the symbols of the life processes. Data sources: Li et al. (2003), NBSC (2003), SECSPC (2004a,b), Zhou (2004), NBSC (2005), Pan and Zhou (2005), Gu et al. (2006), Wang et al. (2006) and GAC (2007).

9 564 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) less well characterized in the public literature, and the losses to the environment and recycling at end-of-life are typically poorly known. Similar situations on data availability and data quality occur in this study on aluminium. Besides the efforts of governmental and industrial organizations to collect and compile them, degree of data uncertainty in different life processes are also greatly influenced by and can be approximately regarded to have a positive correlation with the number of organizations processing, producing or utilizing ACPs and the number of types of ACPs as shown in Fig. 4. For example, China s alumina refining concentrated in only six factories in 2002, which made it easy for CNMIA to calculate the production of alumina and the overall recovery rate of alumina at national level by investigating all these six factories. Collection of data on production of primary aluminium and quantity loss rate in PAS process also seemed not so difficult because there were 130 primary aluminium smelters in China in 2002, which allowed CNMIA capable to investigate most of them, although data uncertainty might be inevitably higher that that of alumina industry. However, for the aluminium recycling industry, because there were more than 2000 refiners/remelters in China in 2002, it was almost impossible for CNMIA or other organizations totally collect data from them. Consequently, data on production of recycled aluminium and loss rate in MS process based on investigation was unavailable in China and could only be acquired from representative information existing in literature or expert interviews. Fig. 5. Anthropogenic aluminium cycles in mainland China for (a) 2001, (b) 2004, and (c) Refer to Table 2 for the symbols of the life processes. The values enclosed in the dotted-line boxes associated with the BM and AR processes indicate the amounts required to close the mass balance. The dashed arrow lines represent the flows of which the data are unavailable or integrated into their parallel flows. All values are in Gg (thousand metric ton) AL per annum. For the trade flows, net import/export (+ denotes net import, whereas denotes net export), instead of gross import/export, is indicated. Width of arrow lines roughly reveals the relative magnitude of flows.

10 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) Fig. 5. (Continued ). Standards on ACPs prescribe the number of types of bauxite, alumina, primary aluminium ingot, wrought alloys, casting alloys, aluminium scrap and recycled aluminium, as well as their aluminium (or aluminium oxide) contents (SECSPC, 2004a,b). For example, alumina has four types, with their contents of aluminium oxide not less than 98.2%, 98.3%, 98.4%, 98.6%, respectively. In this study, we assumed that the average content was 98.4% and surely this data was of low uncertainty. However, aluminium scrap comprises more than 40 types, with their aluminium contents in the range of 80% 98%. We assumed the average aluminium content of imported scrap to be 84% and obviously higher uncertainty was inevitable for this data than that of alumina. 5. Results and discussion Fig. 5 depicts the contemporary anthropogenic aluminium cycles in mainland China for 2001, 2004 and For each solid line rectangle in Fig. 5 which denotes a life process, mass balance ought to be achieved, that is, input flows are equal to output flows plus additions to or subtraction from stock associated with that process. However in practice, it is often the case that mathematical closure is not achieved, perhaps because some flows are determined inaccurately, because flows refer to different but unstated aggregations, or because the amount of material added to or subtracted from stock is unknown (Graedel et al., 2005). In this study, we used dotted-line boxes to indicate the amounts required to close the mass balance for BM and AR processes. Theoretically, because part of bauxite and alumina were used for non-metallurgical application, inputs to the BM and AR processes should be higher than their respective outputs, namely, the values in the dotted-line boxes associated with the BM and AR processes in Fig. 5 should be positive. However, as illustrated by Fig. 5, the differences between inputs and outputs for BM in 2001 and AR in 2004 were negative. Therefore, the amounts of bauxite and alumina used for non-metallurgical application could not be calculated based on the existing data which were obviously not accurate enough Growths and structural changes of production Fig. 6 shows the production of ACPs generated from each life process in China for 2001, 2004 and It is obvious that for every life process, the production in 2007 was higher than that in 2004, and the production in 2004 was more than that in For bauxite, the production was 2042 Gg in 2001, 5565 Gg in 2004 and 6495 Gg in Together with the aluminium loss caused by extraction, the production of bauxite resulted in 2692 Gg, 7170 Gg and 8184 Gg of depletion of domestic ore stock for the 3 years, respectively. Considering that the reserve base of aluminium contained in bauxite in China was Gg by the end of 2003 (Xiao, 2007), the depletion time of bauxite in China, if calculated by dividing the reserve base by the depletion of ore stock in 2007, was less than 25 years. Furthermore, if the depletion of ore stock increases at the rate of 7%, that is, at least the same rate as Chinese economic growth (some 7 10% per annum), the depletion time of bauxite will be less than 15 years. This situation implies that China will have to import more and more bauxite in the next Fig. 6. Production of ACPs generated from each life process in mainland China for 2001, 2004, and All values are in Gg (thousand metric ton) AL per annum. Refer to Table 2 for the symbols of the life processes.

11 566 W. Chen et al. / Resources, Conservation and Recycling 54 (2010) several decades. For alumina, the production in 2001 was 2475 Gg. It then increased by 47% from 2001 to 2004 and more than 180% from 2004 to For primary aluminium, the production growth rates from 2001 to 2004 and from 2004 to 2007 were both about 87%. As calculated by the fixed-lifetime approach, the generation of EOL products in China depended on the amount of aluminium entering the Use stage 12 years ago. Together with the imported EOL products and aluminum scrap which was regarded as old scrap before treatment, the generation of domestic EOL products resulted in 1134 Gg, 2204 Gg and 3705 Gg of aluminium scrap production in 2001, 2004 and 2007, respectively. For recycled aluminium, the production was 1055 Gg in 2001, 2050 Gg in 2004 and 3445 Gg in Considering the production of primary aluminium, the share of recycled aluminium production in unwrought aluminium (including primary and recycled aluminium) production was 22.9% in 2001, 23.5% in 2004 and 21.6% in The production growth of both primary aluminium and recycled aluminium from 2001 to 2007 led to the production growth of semi-finished products (including wrought products and foundry castings) in the same period. For wrought products, the production was 2276 Gg in 2001, and then increased by 133% from 2001 to 2004 and 130% from 2004 to A majority of wrought products produced in China was extrusions, which accounted for about 53%, 63% and 62% of total wrought products production for the 3 years, respectively. Besides, the share of rolled products was 33%, 35% and 35%, respectively, with the remainder belonging to other wrought products. Statistical data on production of foundry castings were not available in China. Therefore, foundry castings production was calculated by a method of mass balance and was 2214 Gg, 2386 Gg and 3070 Gg, and accounted for 49%, 31% and 20% of total production of semi-finished products for the 3 years, respectively. For final products, the production was 4742 Gg in 2001, 7855 Gg in 2004 and 14,110 Gg in However unfortunately, data on the production of final products by end-use categories are not available in China as yet Amounts and structural changes of aluminium trade Fig. 7 shows the import and export of ACPs generated from each life process in 2001, 2004 and 2007 for mainland China. It is obvious that the export of bauxite, alumina, EOL products and scrap, which serve as raw materials to produce unwrought aluminium, were all almost equal to zero. For bauxite, the net import in 2001 and 2004 was 94 Gg and 239 Gg, respectively. It then jumped by almost 2500% from 2004 to 2007, mainly because of the great expansion of alumina production capacity after 2004, as well as the lack of domestic ore stock. For Fig. 7. Import and export of ACPs generated from each life process in mainland China for 2001, 2004, and All values are in Gg (thousand metric ton) AL per annum. Refer to Table 2 for the symbols of the life processes. alumina, the net import was 1714 Gg in 2001, and then increased by 76% from 2001 to 2004 owing to the expansion of primary aluminium production capacity. However, because of the increase of alumina production after 2004, its net import decreased by 13% from 2004 to For EOL products, as mentioned previously, we directly estimated its net import according to expert interviews and literature, which was 200 Gg in 2001, 350 Gg in 2004 and 500 Gg in For aluminium scrap, the net import in 2001 was 302 Gg; it then increased by more than 230% from 2001 to 2004 and 75% from 2004 to As described by Table 3, in the customs statistics, unwrought aluminium is divided into unwrought not-alloyed aluminium and unwrought aluminium alloys rather than primary aluminium and recycled aluminium. In this study, we assumed that all of the unwrought not-alloyed aluminium, as well as 20% of the unwrought aluminium alloys, were primary aluminium; whereas the 80% remainder of unwrought aluminium alloys were recycled aluminium. Different from bauxite, alumina, EOL products and scrap, of which the exports were almost equal to zero while the imports were relatively large, the import and export of unwrought aluminium were basically of the same order of magnitudes. For unwrought primary aluminium, China was a net exporter for the 3 years. From 2001 to 2004, its net export increased by almost 20 times, mainly because the production of primary aluminium greatly increased and there were export tariff rebate for unwrought aluminium at the rate of 15% in the same period. However, Chinese Central Government reduced the rate of export tariff rebate for unwrought aluminium from 15% to 8% on April 1, 2004 and from 8% to 0% on May 1, Furthermore, the Central Government began to impose export tariff on unwrought aluminium at the rate of 5% on May 1, 2005 and increased the rate of export tariff on unwrought not-alloyed aluminium from 5% to 15% on November 1, As a result of these tariffs polices, its net export in 2007 was reduced by 87% as compared with Changes of unwrought recycled aluminium trade showed a different feature. In 2001 and 2004, China was a net importer of recycled aluminium, with the amount of net import equal to 139 Gg in 2001 and 42 Gg in Different from unwrought not-alloyed aluminium, the export tariff on unwrought aluminium alloys was canceled on July 1, Consequently, its net export increased to 157 Gg in For wrought products, both import and export increased from 2001 to 2007, but at different rates. The imports increased by 52% from 2001 to 2004 and 12% from 2004 to However, the exports rose by almost 220% from 2001 to 2004, and then jumped by more than three times from 2004 to As a result, China s net import of wrought products decreased from 2001 to Moreover, China became a net exporter in These changes were probably because of the increase of production of unwrought aluminium and wrought products as mentioned before, also because many of the unwrought primary aluminium, when restricted to be exported directly, were then exported in the form of wrought products after fabrication. Rolled products and extrusions played different roles in the trade of wrought products. Rolled products dominated the imports, while a majority of wrought products exports was extrusions. As a result, China became a net exporter of extrusions in 2004, and its amount of net export in 2007 increased by nearly 450% over In 2007, China also became a net exporter of rolled products, but the amount of it only equal to 22% of that of extrusions. This situation was consistent with the fact that a majority of wrought products produced in China were extrusions as mentioned previously. For other wrought products of which only aluminium powders were included in the customs statistics, the amounts of import and export were relatively small and therefore could be neglected. For final products, as illustrated by Figs. 7 and 8, the import was too small if compared with the export. Therefore, China was a net